Misplaced Pages

#794205

202-448: The Holocene extinction follows the extinction of the majority of large (megafaunal) animals during the preceding Late Pleistocene . Some of these extinctions were likely in part due to human hunting pressure. The most popular theory is that human overhunting of species added to existing stress conditions as the Holocene extinction coincides with human colonization of many new areas around

404-572: A 2022 study published in Frontiers in Ecology and the Environment , a survey of more than 3,000 experts says that the extent of the mass extinction might be greater than previously thought, and estimates that roughly 30% of species "have been globally threatened or driven extinct since the year 1500." In a 2022 report, IPBES listed unsustainable fishing, hunting, and logging as some of the primary drivers of

606-591: A 2006 report by the Food and Agriculture Organization (FAO) of the United Nations, Livestock's Long Shadow , also found that the livestock sector is a "leading player" in biodiversity loss. More recently, in 2019, the IPBES Global Assessment Report on Biodiversity and Ecosystem Services attributed much of this ecological destruction to agriculture and fishing, with the meat and dairy industries having

808-500: A cause of the extinctions argue that statistical modelling validates that relatively low-level hunting can have significant effect on megafauna populations due to their slow life cycles, and that hunting can cause top-down forcing trophic cascade events that destabilize ecosystems. The Second-Order Predation Hypothesis says that as humans entered the New World they continued their policy of killing predators, which had been successful in

1010-485: A collapse in faunal density and diversity across the globe. The extinctions during the Late Pleistocene are differentiated from previous extinctions by its extreme size bias towards large animals (with small animals being largely unaffected), and widespread absence of ecological succession to replace these extinct megafaunal species, and the regime shift of previously established faunal relationships and habitats as

1212-501: A combined 50 billion years of Earth's evolutionary history (defined as phylogenetic diversity) and driving to extinction some of the "most unique animals on the planet," among them the Aye-aye lemur, the Chinese crocodile lizard and the pangolin . Said lead author Rikki Gumbs: We know from all the data we have for threatened species, that the biggest threats are agriculture expansion and

1414-523: A computer model, the Pleistocene extinction model (PEM), which, using the same assumptions and values for all variables (herbivore population, herbivore recruitment rates, food needed per human, herbivore hunting rates, etc.) other than those for hunting of predators. It compares the overkill hypothesis (predator hunting = 0) with second-order predation (predator hunting varied between 0.01 and 0.05 for different runs). The findings are that second-order predation

1616-607: A consequence. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. Human impact on megafauna populations is thought to have been driven by hunting ("overkill"), as well as possibly environmental alteration. The relative importance of human vs climatic factors in the extinctions has been the subject of long-running controversy. Major extinctions occurred in Australia-New Guinea ( Sahul ) beginning approximately 50,000 years ago and in

1818-616: A divide among researches about when and how megafaunal species went extinct. There are at least three hypotheses regarding the extinction of the Australian megafauna : This theory is based on evidence of megafauna surviving until 40,000 years ago, a full 30,000 years after homo sapiens first landed in Australia, and thus that the two groups coexisted for a long time. Evidence of these animals existing at that time come from fossil records and ocean sediment. To begin with, sediment core drilled in

2020-434: A few thousand years, around the 45,000 years ago, suggesting a rapid extinction event. In addition, fossils found at South Walker Creek, which is the youngest megafauna site in northern Australia, indicate that at least 16 species of megafauna survived there until 40,000 years ago. Furthermore, there is no firm evidence of homo sapiens living at South Walker Creek 40,000 years ago, therefore no human cause can be attributed to

2222-577: A formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch. Nevertheless, the definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult. An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have outlined a template to improve the pre-Cryogenian geologic time scale based on

SECTION 10

#1732858408795

2424-577: A fringe theory. Contemporary human overpopulation and continued population growth , along with per-capita consumption growth, prominently in the past two centuries, are regarded as the underlying causes of extinction. Inger Andersen , the executive director of the United Nations Environment Programme , stated that "we need to understand that the more people there are, the more we put the Earth under heavy pressure. As far as biodiversity

2626-461: A geochronologic unit can be changed (and is more often subject to change) when refined by geochronometry while the equivalent chronostratigraphic unit (the revision of which is less frequent) remains unchanged. For example, in early 2022, the boundary between the Ediacaran and Cambrian periods (geochronologic units) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at

2828-670: A global mass extinction of wildlife. We ignore the decline of other species at our peril – for they are the barometer that reveals our impact on the world that sustains us. A 2023 study published in Current Biology concluded that current biodiversity loss rates could reach a tipping point and inevitably trigger a total ecosystem collapse. Recent extinctions are more directly attributable to human influences, whereas prehistoric extinctions can be attributed to other factors. The International Union for Conservation of Nature (IUCN) characterizes 'recent' extinction as those that have occurred past

3030-455: A global scale and eliminate billions of years of phylogenetic diversity . 189 countries, which are signatory to the Convention on Biological Diversity (Rio Accord), have committed to preparing a Biodiversity Action Plan , a first step at identifying specific endangered species and habitats, country by country. For the first time since the demise of the dinosaurs 65 million years ago, we face

3232-505: A global scale, and when these alterations caused changes to global climate. Using chemical proxies from Antarctic ice cores, researchers have estimated the fluctuations of carbon dioxide (CO 2 ) and methane (CH 4 ) gases in the Earth's atmosphere during the Late Pleistocene and Holocene epochs. Estimates of the fluctuations of these two gases in the atmosphere, using chemical proxies from Antarctic ice cores, generally indicate that

3434-465: A great deal of influence over food webs and climatic systems worldwide. Although significant debate exists as to how much human predation and indirect effects contributed to prehistoric extinctions, certain population crashes have been directly correlated with human arrival. Human activity has been the main cause of mammalian extinctions since the Late Pleistocene. A 2018 study published in PNAS found that since

3636-610: A longer Holocene extinction. The Holocene–Anthropocene boundary is contested, with some commentators asserting significant human influence on climate for much of what is normally regarded as the Holocene Epoch . Some experts mark the transition from the Holocene to the Anthropocene at the onset of the industrial revolution . They also note that the official use of this term in the near future will heavily rely on its usefulness, especially for Earth scientists studying late Holocene periods. It has been suggested that human activity has made

3838-617: A machine-readable Resource Description Framework / Web Ontology Language representation of the time scale, which is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end-point. Some other planets and satellites in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus , Mars and

4040-444: A mass extinction event, the sixth in roughly 540 million years, wherein many current life forms could be extirpated or at least committed to extinction by the end of this century." The World Wide Fund for Nature 's 2020 Living Planet Report says that wildlife populations have declined by 68% since 1970 as a result of overconsumption , population growth , and intensive farming , which is further evidence that humans have unleashed

4242-533: A more continental climate than Pleistocene or modern (post-Pleistocene, interglacial) North America. The animals that became extinct actually should have prospered during the shift from mixed woodland-parkland to prairie, because their primary food source, grass, was increasing rather than decreasing. Although the vegetation did become more spatially specialized, the amount of prairie and grass available increased, which would have been good for horses and for mammoths, and yet they became extinct. This criticism ignores

SECTION 20

#1732858408795

4444-427: A much lower extinction rate than this outlying estimate. Theoretical ecologist Stuart Pimm stated that the extinction rate for plants is 100 times higher than normal. Some contend that contemporary extinction has yet to reach the level of the previous five mass extinctions, and that this comparison downplays how severe the first five mass extinctions were. John Briggs argues that there is inadequate data to determine

4646-421: A number of human-derived factors are recognized as contributing to rising atmospheric concentrations of CH 4 (methane) and CO 2 (carbon dioxide), deforestation and territorial clearance practices associated with agricultural development may have contributed most to these concentrations globally in earlier millennia. Scientists that are employing a variance of archaeological and paleoecological data argue that

4848-424: A period of cooling. In between these extremes megafaunal extinctions have occurred progressively in such places as North America, South America and Madagascar with no climatic commonality. The only common factor that can be ascertained is the arrival of humans. This phenomenon appears even within regions. The mammal extinction wave in Australia about 50,000 years ago coincides not with known climatic changes, but with

5050-471: A relative interval of geologic time. A chronostratigraphic unit is a body of rock, layered or unlayered, that is defined between specified stratigraphic horizons which represent specified intervals of geologic time. They include all rocks representative of a specific interval of geologic time, and only this time span. Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic units. A geochronologic unit

5252-469: A reliable chronology. North American extinctions (noted as herbivores ( H ) or carnivores ( C )) included: The survivors are in some ways as significant as the losses: bison ( H ), grey wolf ( C ), lynx ( C ), grizzly bear ( C ), American black bear ( C ), deer (e.g. caribou , moose , wapiti (elk) , Odocoileus spp.) ( H ), pronghorn ( H ), white-lipped peccary ( H ), muskox ( H ), bighorn sheep ( H ), and mountain goat ( H );

5454-800: A similar study drawing on work at the University of Queensland , which found that "more than 1,200 species globally face threats to their survival in more than 90% of their habitat and will almost certainly face extinction without conservation intervention". Since 1970, the populations of migratory freshwater fish have declined by 76%, according to research published by the Zoological Society of London in July 2020. Overall, around one in three freshwater fish species are threatened with extinction due to human-driven habitat degradation and overfishing. Some scientists and academics assert that industrial agriculture and

5656-803: A sixth mass extinction event caused by anthropogenic activity is currently under way. A December 2022 study published in Science Advances states that "the planet has entered the sixth mass extinction" and warns that current anthropogenic trends, particularly regarding climate and land-use changes , could result in the loss of more than a tenth of plant and animal species by the end of the century. 12% of all bird species are threatened with extinction. A 2023 study published in Biological Reviews found that, of 70,000 monitored species, some 48% are experiencing population declines from anthropogenic pressures, whereas only 3% have increasing populations. According to

5858-522: A sixth mass extinction event; however, this finding has been disputed by one 2020 study, which posits that this major decline was primarily driven by a few extreme outlier populations, and that when these outliers are removed, the trend shifts to that of a decline between the 1980s and 2000s, but a roughly positive trend after 2000. A 2021 report in Frontiers in Conservation Science which cites both of

6060-429: A specific and reliable order. This allows for a correlation of strata even when the horizon between them is not continuous. The geologic time scale is divided into chronostratigraphic units and their corresponding geochronologic units. The subdivisions Early and Late are used as the geochronologic equivalents of the chronostratigraphic Lower and Upper , e.g., Early Triassic Period (geochronologic unit)

6262-498: A sufficient mix of food to avoid toxins, they extract enough nutrition from forage to reproduce effectively and the timing of their gestation is not an issue. Of course, this criticism ignores the obvious fact that present-day horses are not competing for resources with ground sloths, mammoths, mastodons, camels, llamas, and bison. Similarly, mammoths survived the Pleistocene Holocene transition on isolated, uninhabited islands in

Holocene extinction - Misplaced Pages Continue

6464-532: A system/series (early/middle/late); however, the International Commission on Stratigraphy advocates for all new series and subseries to be named for a geographic feature in the vicinity of its stratotype or type locality . The name of stages should also be derived from a geographic feature in the locality of its stratotype or type locality. Informally, the time before the Cambrian is often referred to as

6666-491: A very few show unambiguous evidence of human hunting of any type of prey whatsoever." Eugene S. Hunn suggests that the birthrate in hunter-gatherer societies is generally too low, that too much effort is involved in the bringing down of a large animal by a hunting party, and that in order for hunter-gatherers to have brought about the extinction of megafauna simply by hunting them to death, an extraordinary amount of meat would have had to have been wasted. Proponents of hunting as

6868-500: A very significant impact. Since the 1970s food production has soared to feed a growing human population and bolster economic growth, but at a huge price to the environment and other species. The report says some 25% of the Earth's ice-free land is used for cattle grazing. A 2020 study published in Nature Communications warned that human impacts from housing, industrial agriculture and in particular meat consumption are wiping out

7070-458: A wider sense, correlating strata across national and continental boundaries based on their similarity to each other. Many of the names below erathem/era rank in use on the modern ICC/GTS were determined during the early to mid-19th century. During the 19th century, the debate regarding Earth's age was renewed, with geologists estimating ages based on denudation rates and sedimentary thicknesses or ocean chemistry, and physicists determining ages for

7272-494: Is a numeric-only, chronologic reference point used to define the base of geochronologic units prior to the Cryogenian. These points are arbitrarily defined. They are used where GSSPs have not yet been established. Research is ongoing to define GSSPs for the base of all units that are currently defined by GSSAs. The standard international units of the geologic time scale are published by the International Commission on Stratigraphy on

7474-479: Is a subdivision of geologic time. It is a numeric representation of an intangible property (time). These units are arranged in a hierarchy: eon, era, period, epoch, subepoch, age, and subage. Geochronology is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g., radiometric dating ) or relative means (e.g., stratigraphic position , paleomagnetism , stable isotope ratios ). Geochronometry

7676-475: Is a way of representing deep time based on events that have occurred throughout Earth's history , a time span of about 4.54 ± 0.05 Ga (4.54 billion years). It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the Cretaceous–Paleogene extinction event , marks

7878-560: Is apt to be water. Large animals also store more fat in their bodies than do medium-sized animals and this should have allowed them to compensate for extreme seasonal fluctuations in food availability. Geologic time scale The geologic time scale or geological time scale ( GTS ) is a representation of time based on the rock record of Earth . It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology that aims to determine

8080-473: Is clear, therefore, that we are now in an altogether exceptional period of the earth's history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared; and it is, no doubt, a much better world for us now they have gone. Yet it is surely a marvellous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large mammalia, not in one place only but over half

8282-488: Is coincident with increasing aridity. Increasingly arid conditions in southeastern Australia during the late Pleistocene may have stressed megafauna, and contributed to their decline. In Sahul (a former continent composed of Australia and New Guinea ), the sudden and extensive spate of extinctions occurred earlier than in the rest of the world. Most evidence points to a 20,000 year period after human arrival circa 63,000 BCE, but scientific argument continues as to

Holocene extinction - Misplaced Pages Continue

8484-457: Is concerned, we are at war with nature." Some scholars assert that the emergence of capitalism as the dominant economic system has accelerated ecological exploitation and destruction, and has also exacerbated mass species extinction. CUNY professor David Harvey , for example, posits that the neoliberal era "happens to be the era of the fastest mass extinction of species in the Earth's recent history". Ecologist William E. Rees concludes that

8686-449: Is estimated at 100 to 1,000 times higher than the background extinction rate , the historically typical rate of extinction (in terms of the natural evolution of the planet); also, the current rate of extinction is 10 to 100 times higher than in any of the previous mass extinctions in the history of Earth. One scientist estimates the current extinction rate may be 10,000 times the background extinction rate , although most scientists predict

8888-401: Is evidence that anthropogenic fire use had major impacts on the local environments in both Australia and North America. At the end of the 19th and beginning of the 20th centuries, when scientists first realized that there had been glacial and interglacial ages, and that they were somehow associated with the prevalence or disappearance of certain animals, they surmised that the termination of

9090-622: Is evidence that the average size of mammalian fauna declined over the course of the Quaternary, a phenomenon that was likely linked to disproportionate hunting of large animals by humans. Extinction through human hunting has been supported by archaeological finds of mammoths with projectile points embedded in their skeletons, by observations of modern naive animals allowing hunters to approach easily and by computer models by Mosimann and Martin, and Whittington and Dyke, and most recently by Alroy. A number of objections have been raised regarding

9292-469: Is impacting larger mammals and birds to a much greater extent than smaller ones, with the body mass of such animals expected to shrink by 25% over the next century. Another 2019 study published in Biology Letters found that extinction rates are perhaps much higher than previously estimated, in particular for bird species. The 2019 Global Assessment Report on Biodiversity and Ecosystem Services lists

9494-536: Is more consistent with extinction than is overkill (results graph at left). The Pleistocene extinction model is the only test of multiple hypotheses and is the only model to specifically test combination hypotheses by artificially introducing sufficient climate change to cause extinction. When overkill and climate change are combined they balance each other out. Climate change reduces the number of plants, overkill removes animals, therefore fewer plants are eaten. Second-order predation combined with climate change exacerbates

9696-537: Is not to be confused with extinction, as it includes both the disappearance of species and declines in abundance. Defaunation effects were first implied at the Symposium of Plant-Animal Interactions at the University of Campinas, Brazil in 1988 in the context of Neotropical forests . Since then, the term has gained broader usage in conservation biology as a global phenomenon. Big cat populations have severely declined over

9898-665: Is rare, though megafauna exploitation has been documented at a number of sites. Fishtail points rapidly disappeared after the extinction of the megafauna, and were replaced by other styles more suited to hunting smaller prey. Some authors have proposed the "Broken Zig-Zag" model, where human hunting and climate change causing a reduction in open habitats preferred by megafauna were synergistic factors in megafauna extinction in South America. A scarcity of reliably dated megafaunal bone deposits has made it difficult to construct timelines for megafaunal extinctions in certain areas, leading to

10100-401: Is the field of geochronology that numerically quantifies geologic time. A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed-upon reference point on a stratigraphic section that defines the lower boundaries of stages on the geologic time scale. (Recently this has been used to define the base of a system) A Global Standard Stratigraphic Age (GSSA)

10302-663: Is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units. The geologic time scale

SECTION 50

#1732858408795

10504-573: Is used in place of Lower Triassic System (chronostratigraphic unit). Rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, e.g., the rocks that represent the Silurian System are the Silurian System and they were deposited during the Silurian Period. This definition means the numeric age of

10706-749: The Americas about 13,000 years ago, coinciding in time with the early human migrations into these regions. Extinctions in northern Eurasia were staggered over tens of thousands of years between 50,000 and 10,000 years ago, while extinctions in the Americas were virtually simultaneous, spanning only 3000 years at most. Overall, during the Late Pleistocene about 65% of all megafaunal species worldwide became extinct, rising to 72% in North America, 83% in South America and 88% in Australia, with all mammals over 1,000 kilograms (2,200 lb) becoming extinct in Australia and

10908-517: The Americas , Madagascar and New Zealand without the earliest humans. The overkill hypothesis, a variant of the hunting hypothesis, was proposed in 1966 by Paul S. Martin, Professor of Geosciences Emeritus at the Desert Laboratory of the University of Arizona . Circumstantially, the close correlation in time between the appearance of humans in an area and extinction there provides weight for this scenario. Radiocarbon dating has supported

11110-598: The Anthropocene is a proposed epoch/series for the most recent time in Earth's history. While still informal, it is a widely used term to denote the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact. As of April 2022 the Anthropocene has not been ratified by the ICS; however, in May 2019 the Anthropocene Working Group voted in favour of submitting

11312-583: The Atlantic , and of the leatherback sea turtle in Malaysia. Since the Late Pleistocene, humans (together with other factors) have been rapidly driving the largest vertebrate animals towards extinction, and in the process interrupting a 66-million-year-old feature of ecosystems, the relationship between diet and body mass, which researchers suggest could have unpredictable consequences. A 2019 study published in Nature Communications found that rapid biodiversity loss

11514-529: The Brothers of Purity , who wrote on the processes of stratification over the passage of time in their treatises . Their work likely inspired that of the 11th-century Persian polymath Avicenna (Ibn Sînâ, 980–1037) who wrote in The Book of Healing (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognised fossils as "petrifications of

11716-706: The Mediterranean Sea until 4,000 to 7,000 years ago, as well as on Wrangel Island in the Siberian Arctic. Additionally, large mammals should have been able to migrate, permanently or seasonally, if they found the temperature too extreme, the breeding season too short, or the rainfall too sparse or unpredictable. Seasons vary geographically. By migrating away from the equator , herbivores could have found areas with growing seasons more favorable for finding food and breeding successfully. Modern-day African elephants migrate during periods of drought to places where there

11918-684: The Ordovician–Silurian extinction events , the Late Devonian extinction , the Permian–Triassic extinction event , the Triassic–Jurassic extinction event , and the Cretaceous–Paleogene extinction event . If the Capitanian extinction event is included among the first-order mass extinctions, the Holocene extinction would correspondingly be known as the "seventh extinction". The Holocene is

12120-600: The Pleistocene . Over the course of the Late Holocene, there were hundreds of extinctions of birds on islands across the Pacific, driven by human settlement of the previously uninhabited islands, with extinctions peaking around 1300 AD. Roughly 12% of avian species have been driven to extinction by human activity over the last 126,000 years, which is double previous estimates. In the twentieth century, human numbers quadrupled, and

12322-530: The Precambrian or pre-Cambrian (Supereon). While a modern geological time scale was not formulated until 1911 by Arthur Holmes , the broader concept that rocks and time are related can be traced back to (at least) the philosophers of Ancient Greece . Xenophanes of Colophon (c. 570–487  BCE ) observed rock beds with fossils of shells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which

SECTION 60

#1732858408795

12524-616: The UNDP 's 2020 Human Development Report , The Next Frontier: Human Development and the Anthropocene : The planet's biodiversity is plunging, with a quarter of species facing extinction, many within decades. Numerous experts believe we are living through, or on the cusp of, a mass species extinction event, the sixth in the history of the planet and the first to be caused by a single organism—us. The 2022 Living Planet Report found that vertebrate wildlife populations have plummeted by an average of almost 70% since 1970, with agriculture and fishing being

12726-453: The Wisconsin ice sheet could have placed enough thermal stress on cold-adapted mammals to cause them to die. Their heavy fur, which helps conserve body heat in the glacial cold, might have prevented the dumping of excess heat, causing the mammals to die of heat exhaustion. Large mammals, with their reduced surface area-to-volume ratio , would have fared worse than small mammals. A study covering

12928-503: The biosphere continues, one-half of Earth's higher lifeforms will be extinct by 2100. A 1998 poll conducted by the American Museum of Natural History found that 70% of biologists acknowledge an ongoing anthropogenic extinction event. In a pair of studies published in 2015, extrapolation from observed extinction of Hawaiian snails led to the conclusion that 7% of all species on Earth may have been lost already. A 2021 study published in

13130-452: The straight-tusked elephant and the narrow-nosed rhinoceros generally going extinct earlier than cold adapted species like the woolly mammoth and woolly rhinoceros . Climate change has been considered a probable major factor in the extinctions, possibly in combination with human hunting. Extinctions in North America were concentrated at the end of the Late Pleistocene, around 13,800–11,400 years Before Present, which were coincident with

13332-427: The "Anthropocene extinction". Anthropocene is a term introduced in 2000. Some now postulate that a new geological epoch has begun, with the most abrupt and widespread extinction of species since the Cretaceous–Paleogene extinction event 66 million years ago. The term "anthropocene" is being used more frequently by scientists, and some commentators may refer to the current and projected future extinctions as part of

13534-494: The "neoliberal paradigm contributes significantly to planetary unraveling" by treating the economy and the ecosphere as totally separate systems, and by neglecting the latter. Major lobbying organizations representing corporations in the agriculture, fisheries, forestry and paper, mining, and oil and gas industries, including the United States Chamber of Commerce , have been pushing back against legislation that could address

13736-410: The Americas, and around 80% globally. Africa, South Asia and Southeast Asia experienced more moderate extinctions than other regions. The Late Pleistocene saw the extinction of many mammals weighing more than 40 kilograms (88 lb), including around 80% of mammals over 1 tonne. The proportion of megafauna extinctions is progressively larger the further the human migratory distance from Africa, with

13938-668: The Commission on Stratigraphy (applied in 1965) to become a member commission of IUGS led to the founding of the ICS. One of the primary objectives of the ICS is "the establishment, publication and revision of the ICS International Chronostratigraphic Chart which is the standard, reference global Geological Time Scale to include the ratified Commission decisions". Following on from Holmes, several A Geological Time Scale books were published in 1982, 1989, 2004, 2008, 2012, 2016, and 2020. However, since 2013,

14140-464: The Earth's Moon . Dominantly fluid planets, such as the giant planets , do not comparably preserve their history. Apart from the Late Heavy Bombardment , events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets. Construction of a time scale that links the planets is, therefore, of only limited relevance to

14342-515: The Earth's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment are still a matter of debate. The geologic history of Earth's Moon has been divided into a time scale based on geomorphological markers, namely impact cratering , volcanism , and erosion . This process of dividing the Moon's history in this manner means that

14544-430: The Holocene extinction can be linked to the human impact on the environment . The Holocene extinction continues into the 21st century, with anthropogenic global warming , human population growth , increasing per capita consumption (especially by the super- affluent ), and meat production and consumption , among others, being the primary drivers of mass extinction. Deforestation , overfishing , ocean acidification ,

14746-447: The ICS has taken responsibility for producing and distributing the ICC citing the commercial nature, independent creation, and lack of oversight by the ICS on the prior published GTS versions (GTS books prior to 2013) although these versions were published in close association with the ICS. Subsequent Geologic Time Scale books (2016 and 2020 ) are commercial publications with no oversight from

14948-404: The ICS, and do not entirely conform to the chart produced by the ICS. The ICS produced GTS charts are versioned (year/month) beginning at v2013/01. At least one new version is published each year incorporating any changes ratified by the ICS since the prior version. The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to

15150-415: The ICS. While some regional terms are still in use, the table of geologic time conforms to the nomenclature , ages, and colour codes set forth by the International Commission on Stratigraphy in the official International Chronostratigraphic Chart. The International Commission on Stratigraphy also provide an online interactive version of this chart. The interactive version is based on a service delivering

15352-505: The Indian Ocean off the SW coast of Australia indicate the existence of a fungus called Sporormiella, which survived off the dung of plant-eating mammals. The abundance of these spores in the sediment prior to 45,000 years ago indicates that many large mammals existed in the southwest Australian landscape until that point. The sediment data also indicates that the megafauna population collapsed within

15554-518: The Indian subcontinent is uncertain due to a lack of reliable dating. Similar issues have been reported for Chinese sites, though there is no evidence for any of the megafaunal taxa having survived into the Holocene in that region. Extinctions in Southeast Asia and South China have been proposed to be the result of environmental shift from open to closed forested habitats. The Palearctic realm spans

15756-665: The International Chronostratigraphic Chart; however, regional terms are still in use in some areas. The numeric values on the International Chronostratigrahpic Chart are represented by the unit Ma (megaannum, for 'million years '). For example, 201.4 ± 0.2 Ma, the lower boundary of the Jurassic Period, is defined as 201,400,000 years old with an uncertainty of 200,000 years. Other SI prefix units commonly used by geologists are Ga (gigaannum, billion years), and ka (kiloannum, thousand years), with

15958-642: The North American Great Lakes region, the population declines of mastodons and mammoths have been found to correlate with climatic fluctuations during the Younger Dryas rather than human activity. In the Argentine Pampas, the flooding of vast swathes of the once much larger Pampas grasslands may have played a role in the extinctions of its megafaunal assemblages. Critics object that since there were multiple glacial advances and withdrawals in

16160-509: The Old World but because they were more efficient and because the fauna, both herbivores and carnivores, were more naive, they killed off enough carnivores to upset the ecological balance of the continent, causing overpopulation , environmental exhaustion, and environmental collapse. The hypothesis accounts for changes in animal, plant, and human populations. The scenario is as follows: The second-order predation hypothesis has been supported by

16362-410: The Pleistocene ice age might be an explanation for the extinctions. The most obvious change associated with the termination of an ice age is the increase in temperature. Between 15,000 BP and 10,000 BP, a 6 °C increase in global mean annual temperatures occurred. This was generally thought to be the cause of the extinctions. According to this hypothesis, a temperature increase sufficient to melt

16564-480: The Pleistocene extinction model. Also, the control of population sizes by predators is not fully supported by observations of modern ecosystems. The hypothesis further assumes decreases in vegetation due to climate change, but deglaciation doubled the habitable area of North America. Any vegetational changes that did occur failed to cause almost any extinctions of small vertebrates, and they are more narrowly distributed on average, which detractors cite as evidence against

16766-667: The Pleistocene populations particularly vulnerable to changes in their environment. Studies propose that the annual mean temperature of the current interglacial that we have seen for the last 10,000 years is no higher than that of previous interglacials, yet most of the same large mammals survived similar temperature increases. In addition, numerous species such as mammoths on Wrangel Island and St. Paul Island survived in human-free refugia despite changes in climate. This would not be expected if climate change were responsible (unless their maritime climates offered some protection against climate change not afforded to coastal populations on

16968-445: The action of gravity. However, it is now known that not all sedimentary layers are deposited purely horizontally, but this principle is still a useful concept. The principle of lateral continuity that states layers of sediments extend laterally in all directions until either thinning out or being cut off by a different rock layer, i.e. they are laterally continuous. Layers do not extend indefinitely; their limits are controlled by

17170-535: The aforementioned studies, says "population sizes of vertebrate species that have been monitored across years have declined by an average of 68% over the last five decades, with certain population clusters in extreme decline, thus presaging the imminent extinction of their species," and asserts "that we are already on the path of a sixth major extinction is now scientifically undeniable." A January 2022 review article published in Biological Reviews builds upon previous studies documenting biodiversity decline to assert that

17372-505: The age of rocks). It is used primarily by Earth scientists (including geologists , paleontologists , geophysicists , geochemists , and paleoclimatologists ) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies , paleomagnetic properties, and fossils . The definition of standardised international units of geologic time

17574-409: The amount and type of sediment in a sedimentary basin , and the geometry of that basin. The principle of cross-cutting relationships that states a rock that cuts across another rock must be younger than the rock it cuts across. The law of included fragments that states small fragments of one type of rock that are embedded in a second type of rock must have formed first, and were included when

17776-407: The arrival of humans on different continents or islands. This was compared against climate reconstructions for the last 90,000 years. The researchers found correlations of human spread and species extinction indicating that the human impact was the main cause of the extinction, while climate change exacerbated the frequency of extinctions. The study, however, found an apparently low extinction rate in

17978-475: The arrival of humans. In addition, large mammal species like the giant kangaroo Protemnodon appear to have succumbed sooner on the Australian mainland than on Tasmania, which was colonised by humans a few thousand years later. A study published in 2015 supported the hypothesis further by running several thousand scenarios that correlated the time windows in which each species is known to have become extinct with

18180-403: The atmosphere was the growth of human agriculture during the Holocene. One of the main theories explaining early Holocene extinctions is historic climate change . The climate change theory has suggested that a change in climate near the end of the late Pleistocene stressed the megafauna to the point of extinction. Some scientists favor abrupt climate change as the catalyst for the extinction of

18382-508: The base of the Cambrian, and thus the boundary between the Ediacaran and Cambrian systems (chronostratigraphic units) has not been changed; rather, the absolute age has merely been refined. Chronostratigraphy is the element of stratigraphy that deals with the relation between rock bodies and the relative measurement of geological time. It is the process where distinct strata between defined stratigraphic horizons are assigned to represent

18584-518: The bodies of plants and animals", with the 13th-century Dominican bishop Albertus Magnus (c. 1200–1280) extending this into a theory of a petrifying fluid. These works appeared to have little influence on scholars in Medieval Europe who looked to the Bible to explain the origins of fossils and sea-level changes, often attributing these to the ' Deluge ', including Ristoro d'Arezzo in 1282. It

18786-429: The case that early farmers involved in systems of agriculture used more land per capita than growers later in the Holocene, who intensified their labor to produce more food per unit of area (thus, per laborer); arguing that agricultural involvement in rice production implemented thousands of years ago by relatively small populations created significant environmental impacts through large-scale means of deforestation. While

18988-586: The conclusion: "The inability of climate to predict the observed population decline of megafauna, especially during the past 75,000 years, implies that human impact became the main driver of megafauna dynamics around this date." Although Africa was one of the least affected regions, the region still suffered extinctions, particularly around the Late Pleistocene-Holocene transition. These extinctions were likely predominantly climatically driven by changes to grassland habitats. The timing of extinctions on

19190-402: The continents, with around 83% of its megafauna going extinct. These extinctions postdate the arrival of modern humans in South America around 15,000 years ago. Both human and climatic factors have been attributed as factors in the extinctions by various authors. Although some megafauna has been historically suggested to have survived into the early Holocene based on radiocarbon dates this may be

19392-566: The cooling of the Earth or the Sun using basic thermodynamics or orbital physics. These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations of Lord Kelvin and Clarence King were held in high regard at the time due to their pre-eminence in physics and geology. All of these early geochronometric determinations would later prove to be incorrect. The discovery of radioactive decay by Henri Becquerel , Marie Curie , and Pierre Curie laid

19594-599: The current available data and the prehistoric overkill hypothesis. For instance, there are ambiguities around the timing of Australian megafauna extinctions. Evidence supporting the prehistoric overkill hypothesis includes the persistence of megafauna on some islands for millennia past the disappearance of their continental cousins. For instance, ground sloths survived on the Antilles long after North and South American ground sloths were extinct, woolly mammoths died out on remote Wrangel Island 6,000 years after their extinction on

19796-578: The current geological epoch . There is no general agreement on when the Holocene , or anthropogenic , extinction begins, and the Quaternary extinction event , which includes climate change resulting in the end of the last ice age , ends, or if they should be considered separate events at all. The Holocene extinction is mainly caused by human activities. Some authors have argued that the activities of earlier archaic humans have also resulted in extinctions, though

19998-510: The cut-off point of 1500, and at least 875 plant and animal species have gone extinct since that time and 2009. Some species, such as the Père David's deer and the Hawaiian crow , are extinct in the wild, and survive solely in captive populations. Other populations are only locally extinct (extirpated), still existent elsewhere, but reduced in distribution, as with the extinction of gray whales in

20200-465: The dawn of human civilization, the biomass of wild mammals has decreased by 83%. The biomass decrease is 80% for marine mammals, 50% for plants, and 15% for fish. Currently, livestock make up 60% of the biomass of all mammals on Earth, followed by humans (36%) and wild mammals (4%). As for birds, 70% are domesticated, such as poultry, whereas only 30% are wild. Extinction of animals, plants, and other organisms caused by human actions may go as far back as

20402-467: The deepest astonishment, on the changed state of [South America]. Formerly it must have swarmed with great monsters, like the southern parts of Africa, but now we find only the tapir, guanaco, armadillo, capybara; mere pigmies compared to antecedents races... Since their loss, no very great physical changes can have taken place in the nature of the Country. What then has exterminated so many living creatures? It

20604-426: The destruction of wetlands , and the decline in amphibian populations , among others, are a few broader examples of global biodiversity loss . Mass extinctions are characterized by the loss of at least 75% of species within a geologically short period of time (i.e., less than 2 million years). The Holocene extinction is also known as the "sixth extinction", as it is possibly the sixth mass extinction event, after

20806-453: The destruction of habitats, the consumption of animals as resources, and the elimination of species that humans view as threats or competitors. Rising extinction trends impacting numerous animal groups including mammals, birds, reptiles, and amphibians have prompted some scientists to declare a biodiversity crisis. The description of recent extinction as a mass extinction has been debated among scientists. Stuart Pimm , for example, asserts that

21008-453: The developments in mass spectrometry pioneered by Francis William Aston , Arthur Jeffrey Dempster , and Alfred O. C. Nier during the early to mid- 20th century would finally allow for the accurate determination of radiometric ages, with Holmes publishing several revisions to his geological time-scale with his final version in 1960. The establishment of the IUGS in 1961 and acceptance of

21210-404: The different layers of stone unless they had been upon the shore and had been covered over by earth newly thrown up by the sea which then became petrified? And if the above-mentioned Deluge had carried them to these places from the sea, you would find the shells at the edge of one layer of rock only, not at the edge of many where may be counted the winters of the years during which the sea multiplied

21412-475: The direct evidence for this includes: fossils of some megafauna found in conjunction with human remains, embedded arrows and tool cut marks found in megafaunal bones, and European cave paintings that depict such hunting. Biogeographical evidence is also suggestive: the areas of the world where humans evolved currently have more of their Pleistocene megafaunal diversity (the elephants and rhinos of Asia and Africa ) compared to other areas such as Australia ,

21614-511: The effect of climate change. (results graph at right). The second-order predation hypothesis is further supported by the observation above that there was a massive increase in bison populations. However, this hypothesis has been criticised on the grounds that the multispecies model produces a mass extinction through indirect competition between herbivore species: small species with high reproductive rates subsidize predation on large species with low reproductive rates. All prey species are lumped in

21816-533: The end of the twentieth century, and continuing into the present day. Pollinators, which are necessary for 75% of food crops, are declining globally in both abundance and diversity. A 2017 study led by Radboud University's Hans de Kroon indicated that the biomass of insect life in Germany had declined by three-quarters in the previous 25 years. Participating researcher Dave Goulson of Sussex University stated that their study suggested that humans are making large parts of

22018-651: The entirety of the European continent and stretches into northern Asia , through the Caucasus and central Asia to northern China , Siberia and Beringia . Extinctions were more severe in Northern Eurasia than in Africa or South and Southeast Asia. These extinctions were staggered over tens of thousands of years, spanning from around 50,000 years Before Present (BP) to around 10,000 years BP, with temperate adapted species like

22220-434: The estimate put forward in the 2019 IPBES report. According to a 2023 study published in PNAS , at least 73 genera of animals have gone extinct since 1500. If humans had never existed, the study estimates it would have taken 18,000 years for the same genera to have disappeared naturally, leading the authors to conclude that "the current generic extinction rates are 35 times higher than expected background rates prevailing in

22422-516: The evidence for this is equivocal; this is supported by rapid megafaunal extinction following recent human colonization in Australia , New Zealand , and Madagascar . In many cases, it is suggested that even minimal hunting pressure was enough to wipe out large fauna, particularly on geographically isolated islands. Only during the most recent parts of the extinction have plants also suffered large losses . The contemporary rate of extinction of species

22624-462: The evolutionary history of many of the megafauna, it is rather implausible that only after the last glacial maximum would there be such extinctions. Proponents of climate change as the extinction event's cause like David J. Meltzer suggest that the last deglaciation may have been markedly different from previous ones. Also, one study suggests that the Pleistocene megafaunal composition may have differed markedly from that of earlier interglacials, making

22826-427: The exact date range. In the rest of the Pacific (other Australasian islands such as New Caledonia, and Oceania ) although in some respects far later, endemic fauna also usually perished quickly upon the arrival of humans in the late Pleistocene and early Holocene. The megafaunal extinctions were already recognized as a distinct phenomenon by some scientists in the 19th century: It is impossible to reflect without

23028-456: The exception of Africa. Over the past 130,000 years, avian functional diversity has declined precipitously and disproportionately relative to phylogenetic diversity losses. Human civilization was founded on and grew from agriculture. The more land used for farming, the greater the population a civilization could sustain, and subsequent popularization of farming led to widespread habitat conversion. Habitat destruction by humans , thus replacing

23230-401: The extinction are automatically to be preferred by default, however, any more than weaknesses in climate change arguments can be taken as supporting overkill. Some form of a combination of both factors could be plausible, and overkill would be a lot easier to achieve large-scale extinction with an already stressed population due to climate change. South America suffered among the worst losses of

23432-550: The extinction crisis. A 2022 report by the climate think tank InfluenceMap stated that "although industry associations, especially in the US, appear reluctant to discuss the biodiversity crisis, they are clearly engaged on a wide range of policies with significant impacts on biodiversity loss." The loss of animal species from ecological communities, defaunation , is primarily driven by human activity. This has resulted in empty forests , ecological communities depleted of large vertebrates. This

23634-471: The extinction event include deforestation , hunting, pollution, the introduction in various regions of non-native species , and the widespread transmission of infectious diseases spread through livestock and crops. Recent investigations into the practice of landscape burning during the Neolithic Revolution have a major implication for the current debate about the timing of the Anthropocene and

23836-453: The extinction of 90% of megafauna species. Several studies provide evidence that climate change caused megafaunal extinction during the Pleistocene in Australia. One group of researchers analyzed fossilized teeth found at Cuddie Springs in southeastern Australia. By analyzing oxygen isotopes , they measured aridity, and by analyzing carbon isotopes and dental microwear texture analysis, they assessed megafaunal diets and vegetation. During

24038-420: The extinction of these megafauna. However, there is evidence of major environmental deterioration of South Water Creek 40,000 years ago, which may have caused the extinct event. These changes include increased fire, reduction in grasslands, and the loss of fresh water. The same environmental deterioration is seen across Australia at the time, further strengthening the climate change argument. Australia's climate at

24240-698: The extinctions. It has been shown that vegetation changed from mixed woodland - parkland to separate prairie and woodland. This may have affected the kinds of food available. Shorter growing seasons may have caused the extinction of large herbivores and the dwarfing of many others. In this case, as observed, bison and other large ruminants would have fared better than horses, elephants and other monogastrics , because ruminants are able to extract more nutrition from limited quantities of high- fiber food and better able to deal with anti-herbivory toxins. So, in general, when vegetation becomes more specialized, herbivores with less diet flexibility may be less able to find

24442-606: The fossil record of mainland Asia. A 2020 study published in Science Advances found that human population size and/or specific human activities, not climate change, caused rapidly rising global mammal extinction rates during the past 126,000 years. Around 96% of all mammalian extinctions over this time period are attributable to human impacts. According to Tobias Andermann, lead author of the study, "these extinctions did not happen continuously and at constant pace. Instead, bursts of extinctions are detected across different continents at times when humans first reached them. More recently,

24644-435: The fossil record" and adds that anthropogenic ecological stressors, including climate change, habitat fragmentation , pollution, overfishing, overhunting, invasive species, and expanding human biomass , will intensify and accelerate extinction rates in the future without significant mitigation efforts. In The Future of Life (2002), Edward Osborne Wilson of Harvard calculated that, if the current rate of human disruption of

24846-414: The foundational principles of determining the correlation of strata relative to geologic time. Over the course of the 18th-century geologists realised that: The apparent, earliest formal division of the geologic record with respect to time was introduced during the era of Biblical models by Thomas Burnet who applied a two-fold terminology to mountains by identifying " montes primarii " for rock formed at

25048-458: The geologic time scale of Earth. This table is arranged with the most recent geologic periods at the top, and the oldest at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. As such, this table is not to scale and does not accurately represent the relative time-spans of each geochronologic unit. While the Phanerozoic Eon looks longer than

25250-444: The global demand for meat. Pasture land, and the clearing of rainforests for production of soy, for me, are the largest drivers – and the direct consumption of animals. Late Pleistocene extinctions The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna (typically defined as animal species having body masses over 44 kilograms (97 lb)), which resulted in

25452-537: The global extinction crisis. A 2022 study published in Science Advances suggests that if global warming reaches 2.7 °C (4.9 °F) or 4.4 °C (7.9 °F) by 2100, then 13% and 27% of terrestrial vertebrate species will go extinct by then, largely due to climate change (62%), with anthropogenic land conversion and co-extinctions accounting for the rest. A 2023 study published in PLOS One shows that around two million species are threatened with extinction, double

25654-492: The ground work for radiometric dating, but the knowledge and tools required for accurate determination of radiometric ages would not be in place until the mid-1950s. Early attempts at determining ages of uranium minerals and rocks by Ernest Rutherford , Bertram Boltwood , Robert Strutt , and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913. The discovery of isotopes in 1913 by Frederick Soddy , and

25856-577: The growing demand for meat is contributing to significant global biodiversity loss as this is a significant driver of deforestation and habitat destruction; species-rich habitats, such as the Amazon region and Indonesia being converted to agriculture. A 2017 study by the World Wildlife Fund (WWF) found that 60% of biodiversity loss can be attributed to the vast scale of feed crop cultivation required to rear tens of billions of farm animals. Moreover,

26058-445: The highest extinction rates in Australia, and North and South America. The increased extent of extinction mirrors the migration pattern of modern humans: the further away from Africa, the more recently humans inhabited the area, the less time those environments (including its megafauna) had to become accustomed to humans (and vice versa). There are two main hypotheses to explain this extinction: There are some inconsistencies between

26260-442: The hunting hypothesis. Notable among them is the sparsity of evidence of human hunting of megafauna. There is no archeological evidence that in North America megafauna other than mammoths, mastodons, gomphotheres and bison were hunted, despite the fact that, for example, camels and horses are very frequently reported in fossil history. Overkill proponents, however, say this is due to the fast extinction process in North America and

26462-441: The hypothesis. In southeastern Australia, the scarcity of water during the interval in which humans arrived in Australia suggests that human competition with megafauna for precious water sources may have played a role in the extinction of the latter. One consequence of the colonisation by humans of lands previously uninhabited by them may have been the introduction of new fire regimes because of extensive fire use by humans. There

26664-520: The increased abundance and broad geographic extent of Pleistocene bison at the end of the Pleistocene, which would have increased competition for these resources in a manner not seen in any earlier interglacials. Although horses became extinct in the New World, they were successfully reintroduced by the Spanish in the 16th century—into a modern post-Pleistocene, interglacial climate. Today there are feral horses still living in those same environments. They find

26866-409: The individuals extinctions tended to occur during times of environmental change and did not correlate particularly well with human migrations. In Australia, some studies have suggested that extinctions of megafauna began before the peopling of the continent, favouring climate change as the driver. In Beringia, megafauna may have gone extinct because of particularly intense paludification and because

27068-421: The issue of the Pleistocene megafauna extinctions, concluding that the extinctons were at least in part the result of human agency in combination with other factors. Discussion of the topic became more widespread during the 20th century, particularly following the proposal of the "overkill hypothesis" by Paul Schultz Martin during the 1960s. By the end of the 20th century, two "camps" of researchers had emerged on

27270-639: The journal Frontiers in Forests and Global Change found that only around 3% of the planet's terrestrial surface is ecologically and faunally intact, meaning areas with healthy populations of native animal species and little or no human footprint. The 2019 Global Assessment Report on Biodiversity and Ecosystem Services , published by the United Nations' Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), posits that out of around eight million species of plants and animals, roughly one million species face extinction within decades as

27472-605: The land connection between Eurasia and North America flooded before the Cordilleran Ice Sheet retreated far enough to reopen the corridor between Beringia and the remainder of North America. Woolly mammoths became extirpated from Beringia because of climatic factors, although human activity also played a synergistic role in their decline. In North America, a Radiocarbon-dated Event-Count (REC) modelling study found that megafaunal declines in North America correlated with climatic changes instead of human population expansion. In

27674-503: The land surface of the globe. We cannot but believe that there must have been some physical cause for this great change; and it must have been a cause capable of acting almost simultaneously over large portions of the earth's surface, and one which, as far as the Tertiary period at least is concerned, was of an exceptional character. Several decades later in his 1911 book The World of Life (published 2 years before his death), Wallace revisited

27876-531: The large variety of extinctions. The causes may involve the interplay of climate change , competition between species , unstable population dynamics , and hunting as well as competition by humans. The original debates as to whether human arrival times or climate change constituted the primary cause of megafaunal extinctions necessarily were based on paleontological evidence coupled with geological dating techniques. Recently, genetic analyses of surviving megafaunal populations have contributed new evidence, leading to

28078-570: The last half-century and could face extinction in the following decades. According to 2011 IUCN estimates: lions are down to 25,000, from 450,000; leopards are down to 50,000, from 750,000; cheetahs are down to 12,000, from 45,000; tigers are down to 3,000 in the wild, from 50,000. A December 2016 study by the Zoological Society of London, Panthera Corporation and Wildlife Conservation Society showed that cheetahs are far closer to extinction than previously thought, with only 7,100 remaining in

28280-415: The last million years under the absence of human impacts" and that human civilization is causing the "rapid mutilation of the tree of life." We are currently, in a systematic manner, exterminating all non-human living beings. — Anne Larigauderie , IPBES executive secretary There is widespread consensus among scientists that human activity is accelerating the extinction of many animal species through

28482-411: The late Pleistocene , over 12,000 years ago. There is a correlation between megafaunal extinction and the arrival of humans. Megafauna that are still extant also suffered severe declines that were highly correlated with human expansion and activity. Over the past 125,000 years, the average body size of wildlife has fallen by 14% as actions by prehistoric humans eradicated megafauna on all continents with

28684-913: The latter often represented in calibrated units ( before present ). The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the suffix (e.g. Phanerozoic Eonothem becomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes in the history of life on Earth: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named for lithology (e.g., Cretaceous), geography (e.g., Permian ), or are tribal (e.g., Ordovician ) in origin. Most currently recognised series and subseries are named for their position within

28886-561: The layers of sand and mud brought down by the neighboring rivers and spread them over its shores. And if you wish to say that there must have been many deluges in order to produce these layers and the shells among them it would then become necessary for you to affirm that such a deluge took place every year. These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against Genesis were not readily accepted and dissent from religious doctrine

29088-438: The leading cause in the next several decades. A June 2020 study published in PNAS posits that the contemporary extinction crisis "may be the most serious environmental threat to the persistence of civilization, because it is irreversible" and that its acceleration "is certain because of the still fast growth in human numbers and consumption rates." The study found that more than 500 vertebrate species are poised to be lost in

29290-482: The list of survivors also include species which were extirpated during the Quaternary extinction event, but recolonised at least part of their ranges during the mid-Holocene from South American relict populations, such as the cougar ( C ), jaguar ( C ), giant anteater ( C ), collared peccary ( H ), ocelot ( C ) and jaguarundi ( C ). All save the pronghorns and giant anteaters were descended from Asian ancestors that had evolved with human predators. Pronghorns are

29492-537: The litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardising globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The International Chronostratigraphic Chart represents this ongoing effort. Several key principles are used to determine

29694-411: The low probability of animals with signs of butchery to be preserved. The majority of North American taxa have too sparse a fossil record to accurately assess the frequency of human hunting of them. A study by Surovell and Grund concluded "archaeological sites dating to the time of the coexistence of humans and extinct fauna are rare. Those that preserve bone are considerably more rare, and of those, only

29896-607: The lower boundary of the Paleogene System/Period and thus the boundary between the Cretaceous and Paleogene systems/periods. For divisions prior to the Cryogenian , arbitrary numeric boundary definitions ( Global Standard Stratigraphic Ages , GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record. Historically, regional geologic time scales were used due to

30098-421: The magnitude of human driven extinctions has picked up the pace again, this time on a global scale." On a related note, the population declines of still extant megafauna during the Pleistocene have also been shown to correlate with human expansion rather than climate change. The extinction's extreme bias towards larger animals further supports a relationship with human activity rather than climate change. There

30300-514: The mainland). Under normal ecological assumptions island populations should be more vulnerable to extinction due to climate change because of small populations and an inability to migrate to more favorable climes. Critics have also identified a number of problems with the continentality hypotheses. Megaherbivores have prospered at other times of continental climate. For example, megaherbivores thrived in Pleistocene Siberia , which had and has

30502-448: The mainland, while Steller's sea cows persisted off the isolated and uninhabited Commander Islands for thousands of years after they had vanished from the continental shores of the north Pacific. The later disappearance of these island species correlates with the later colonization of these islands by humans. Still, there are some arguments that species responded differently to environmental changes, and no one factor by itself explains

30704-546: The megafauna at the end of the Pleistocene, most who believe increased hunting from early modern humans also played a part, with others even suggesting that the two interacted. In the Americas, a controversial explanation for the shift in climate is presented under the Younger Dryas impact hypothesis , which states that the impact of comets cooled global temperatures. Despite its popularity among nonscientists, this hypothesis never been accepted by relevant experts, who dismiss it as

30906-701: The megafaunal extinctions and that Africa's trans-equatorial position allowed rangeland to continue to exist between the deserts and the central forests, therefore fewer megafauna species became extinct there. Evidence in Southeast Asia, in contrast to Europe, Australia, and the Americas, suggests that climate change and an increasing sea level were significant factors in the extinction of several herbivorous species. Alterations in vegetation growth and new access routes for early humans and mammals to previously isolated, localized ecosystems were detrimental to select groups of fauna. Some evidence from Europe also suggests climatic changes were responsible for extinctions there, as

31108-492: The middle Pleistocene, southeastern Australia was dominated by browsers, including fauna that consumed C4 plants . By the late Pleistocene, the C4 plant dietary component had decreased considerably. This shift may have been caused by increasingly arid conditions, which may have caused dietary restrictions. Other isotopic analyses of eggshells and wombat teeth also point to a decline of C4 vegetation after 45 Ka. This decline in C4 vegetation

31310-551: The mix of vegetation they need to sustain life and reproduce, within a given area. Increased continentality resulted in reduced and less predictable rainfall limiting the availability of plants necessary for energy and nutrition. It has been suggested that this change in rainfall restricted the amount of time favorable for reproduction. This could disproportionately harm large animals, since they have longer, more inflexible mating periods, and so may have produced young at unfavorable seasons (i.e., when sufficient food, water, or shelter

31512-407: The next two decades. Biomass of mammals on Earth as of 2018 Humans both create and destroy crop cultivar and domesticated animal varieties. Advances in transportation and industrial farming has led to monoculture and the extinction of many cultivars. The use of certain plants and animals for food has also resulted in their extinction, including silphium and the passenger pigeon . It

31714-526: The onset of the Younger Dryas cooling period, as well as the emergence of the hunter-gatherer Clovis culture . The relative importance of human and climactic factors in the North American extinctions has been the subject of significant controversy. Extinctions totalled around 35 genera. The radiocarbon record for North America south of the Alaska-Yukon region has been described as "inadequate" to construct

31916-420: The original local ecosystems, is a major driver of extinction. The sustained conversion of biodiversity rich forests and wetlands into poorer fields and pastures (of lesser carrying capacity for wild species), over the last 10,000 years, has considerably reduced the Earth's carrying capacity for wild birds and mammals, among other organisms, in both population size and species count. Other, related human causes of

32118-650: The past 56,000 years indicates that rapid warming events with temperature changes of up to 16 °C (29 °F) had an important impact on the extinction of megafauna. Ancient DNA and radiocarbon data indicates that local genetic populations were replaced by others within the same species or by others within the same genus. Survival of populations was dependent on the existence of refugia and long distance dispersals, which may have been disrupted by human hunters. Other scientists have proposed that increasingly extreme weather—hotter summers and colder winters—referred to as " continentality ", or related changes in rainfall caused

32320-430: The patterns of the significant decline of CO 2 levels during the last ice age of the Pleistocene inversely correlate to the Holocene where there have been dramatic increases of CO 2 around 8000 years ago and CH 4 levels 3000 years after that. The correlation between the decrease of CO 2 in the Pleistocene and the increase of it during the Holocene implies that the causation of this spark of greenhouse gases into

32522-511: The peak of the Anthropocene occurred within the previous two centuries: typically beginning with the Industrial Revolution , when the highest greenhouse gas levels were recorded. A 2015 article in Science suggested that humans are unique in ecology as an unprecedented "global superpredator", regularly preying on large numbers of fully grown terrestrial and marine apex predators , and with

32724-524: The period starting from the mid-20th century different enough from the rest of the Holocene to consider it a new geological epoch , known as the Anthropocene, a term which was considered for inclusion in the timeline of Earth's history by the International Commission on Stratigraphy in 2016, but the proposal was rejected in 2024. To constitute the Holocene as an extinction event , scientists must determine exactly when anthropogenic greenhouse gas emissions began to measurably alter natural atmospheric levels on

32926-408: The pertinent time span. As of April 2022 these proposed changes have not been accepted by the ICS. The proposed changes (changes from the current scale [v2023/09]) are italicised: Proposed pre-Cambrian timeline (GTS2012), shown to scale: Current ICC pre-Cambrian timeline (v2023/09), shown to scale: The following table summarises the major events and characteristics of the divisions making up

33128-524: The planet uninhabitable for wildlife. Goulson characterized the situation as an approaching "ecological Armageddon", adding that "if we lose the insects then everything is going to collapse." A 2019 study found that over 40% of insect species are threatened with extinction. The most significant drivers in the decline of insect populations are associated with intensive farming practices, along with pesticide use and climate change. The world's insect population decreases by around 1 to 2% per year. We have driven

33330-519: The plausibility of this correlation being reflective of causation. The megafaunal extinctions covered a vast period of time and highly variable climatic situations. The earliest extinctions in Australia were complete approximately 50,000 BP, well before the Last Glacial Maximum and before rises in temperature. The most recent extinction in New Zealand was complete no earlier than 500 BP and during

33532-452: The present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline. Horizontal scale is Millions of years (above timelines) / Thousands of years (below timeline) First suggested in 2000,

33734-466: The primary causes of contemporary extinctions in descending order: (1) changes in land and sea use (primarily agriculture and overfishing respectively); (2) direct exploitation of organisms such as hunting; (3) anthropogenic climate change; (4) pollution and (5) invasive alien species spread by human trade. This report, along with the 2020 Living Planet Report by the WWF, both project that climate change will be

33936-618: The primary drivers of this decline. Some scientists, including Rodolfo Dirzo and Paul R. Ehrlich , contend that the sixth mass extinction is largely unknown to most people globally and is also misunderstood by many in the scientific community. They say it is not the disappearance of species, which gets the most attention, that is at the heart of the crisis, but "the existential threat of myriad population extinctions." The abundance of species extinctions considered anthropogenic , or due to human activity, has sometimes (especially when referring to hypothesized future events) been collectively called

34138-485: The principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships. From this Steno reasoned that strata were laid down in succession and inferred relative time (in Steno's belief, time from Creation ). While Steno's principles were simple and attracted much attention, applying them proved challenging. These basic principles, albeit with improved and more nuanced interpretations, still form

34340-433: The processes contributing to substantial human modification of the environment spanned many thousands of years on a global scale and thus, not originating as late as the Industrial Revolution . Palaeoclimatologist William Ruddiman has argued that in the early Holocene 11,000 years ago, atmospheric carbon dioxide and methane levels fluctuated in a pattern which was different from the Pleistocene epoch before it. He argued that

34542-620: The rate of biological extinction, the permanent loss of species, up several hundred times beyond its historical levels, and are threatened with the loss of a majority of all species by the end of the 21st century. Various species are predicted to become extinct in the near future , among them some species of rhinoceros , primates , and pangolins . Others, including several species of giraffe, are considered " vulnerable " and are experiencing significant population declines from anthropogenic impacts including hunting, deforestation and conflict. Hunting alone threatens bird and mammalian populations around

34744-408: The real rate of extinctions, and shows that estimates of current species extinctions varies enormously, ranging from 1.5 species to 40,000 species going extinct due to human activities each year. Both papers from Barnosky et al. (2011) and Hull et al. (2015) point out that the real rate of extinction during previous mass extinctions is unknown, because only some organisms leave fossil remains, and also

34946-521: The relative relationships of rocks and thus their chronostratigraphic position. The law of superposition that states that in undeformed stratigraphic sequences the oldest strata will lie at the bottom of the sequence, while newer material stacks upon the surface. In practice, this means a younger rock will lie on top of an older rock unless there is evidence to suggest otherwise. The principle of original horizontality that states layers of sediments will originally be deposited horizontally under

35148-502: The reproductive effort when circumstances once more favored offspring survival. A study looking at the environmental conditions across Europe, Siberia and the Americas from 25,000 to 10,000 YBP found that prolonged warming events leading to deglaciation and maximum rainfall occurred just prior to the transformation of the rangelands that supported megaherbivores into widespread wetlands that supported herbivore-resistant plants. The study proposes that moisture-driven environmental change led to

35350-467: The rest, it merely spans ~539 million years (~12% of Earth's history), whilst the previous three eons collectively span ~3,461 million years (~76% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic). The use of subseries/subepochs has been ratified by

35552-599: The result of dating errors due to contamination. The extinctions are coincident with the end of the Antarctic Cold Reversal (a cooling period earlier and less severe than the Northern Hemisphere Younger Dryas) and the emergence of Fishtail projectile points , which became widespread across South America. Fishtail projectile points are thought to have been used in big game hunting, though direct evidence of exploitation of extinct megafauna by humans

35754-496: The result of human actions. Organized human existence is jeopardised by increasingly rapid destruction of the systems that support life on Earth, according to the report, the result of one of the most comprehensive studies of the health of the planet ever conducted. Moreover, the 2021 Economics of Biodiversity review, published by the UK government, asserts that "biodiversity is declining faster than at any time in human history." According to

35956-630: The rock record to bring it in line with the post-Tonian geologic time scale. This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian, and the proposals in the "Geological Time Scale" books 2004, 2012, and 2020. Their recommend revisions of the pre-Cryogenian geologic time scale were (changes from the current scale [v2023/09] are italicised): Proposed pre-Cambrian timeline (Shield et al. 2021, ICS working group on pre-Cryogenian chronostratigraphy), shown to scale: Current ICC pre-Cambrian timeline (v2023/09), shown to scale: The book, Geologic Time Scale 2012,

36158-478: The role that humans may have played in the production of greenhouse gases prior to the Industrial Revolution . Studies of early hunter-gatherers raise questions about the current use of population size or density as a proxy for the amount of land clearance and anthropogenic burning that took place in pre-industrial times. Scientists have questioned the correlation between population size and early territorial alterations. Ruddiman and Ellis' research paper in 2009 makes

36360-474: The sea had at times transgressed over the land and at other times had regressed . This view was shared by a few of Xenophanes's contemporaries and those that followed, including Aristotle (384–322 BCE) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of deep time was also recognised by Chinese naturalist Shen Kuo (1031–1095) and Islamic scientist -philosophers, notably

36562-544: The second rock was forming. The relationships of unconformities which are geologic features representing a gap in the geologic record. Unconformities are formed during periods of erosion or non-deposition, indicating non-continuous sediment deposition. Observing the type and relationships of unconformities in strata allows geologist to understand the relative timing the strata. The principle of faunal succession (where applicable) that states rock strata contain distinctive sets of fossils that succeed each other vertically in

36764-403: The second-fastest land mammal (after the cheetah ), which may have helped them elude hunters. More difficult to explain in the context of overkill is the survival of bison, since these animals first appeared in North America less than 240,000 years ago and so were geographically removed from human predators for a sizeable period of time. Because ancient bison evolved into living bison, there

36966-444: The sixth mass extinction "is something that hasn't happened yet – we are on the edge of it." Several studies posit that the Earth has entered a sixth mass extinction event, including a 2015 paper by Barnosky et al. and a November 2017 statement titled " World Scientists' Warning to Humanity: A Second Notice ", led by eight authors and signed by 15,364 scientists from 184 countries which asserted, among other things, that "we have unleashed

37168-555: The size of the global economy increased twenty-five-fold. This Great Acceleration or Anthropocene epoch has also accelerated species extinction. Ecologically , humanity is now an unprecedented "global superpredator", which consistently preys on the adults of other apex predators , takes over other species' essential habitats and displaces them, and has worldwide effects on food webs . There are many famous examples of extinctions within Africa , Asia , Europe , Australia , North and South America , and on smaller islands. Overall,

37370-412: The temporal resolution of the fossil layer is larger than the time frame of the extinction events. However, all these authors agree that there is a modern biodiversity crisis with population declines affecting numerous species, and that a future anthropogenic mass extinction event is a big risk. The 2011 study by Barnosky et al. confirms that "current extinction rates are higher than would be expected from

37572-424: The time could best be described as an overall drying of the landscape due to lower precipitation, resulting in less fresh water availability and more drought conditions. Overall, this led to changes in vegetation, increased fires, overall reduction in grasslands, and a greater competition for already scarce fresh water. These environmental changes proved to be too much for the Australian megafauna to cope with, causing

37774-433: The time during which the rocks were laid down, and the collection of rocks themselves (i.e., it was correct to say Tertiary rocks, and Tertiary Period). Only the Quaternary division is retained in the modern geologic time scale, while the Tertiary division was in use until the early 21st century. The Neptunism and Plutonism theories would compete into the early 19th century with a key driver for resolution of this debate being

37976-730: The time of the 'Deluge', and younger " monticulos secundarios" formed later from the debris of the " primarii" . Anton Moro (1687–1784) also used primary and secondary divisions for rock units but his mechanism was volcanic. In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on by Giovanni Targioni Tozzetti (1712–1783) and Giovanni Arduino (1713–1795) to include tertiary and quaternary divisions. These divisions were used to describe both

38178-562: The time scale boundaries do not imply fundamental changes in geological processes, unlike Earth's geologic time scale. Five geologic systems/periods ( Pre-Nectarian , Nectarian , Imbrian , Eratosthenian , Copernican ), with the Imbrian divided into two series/epochs (Early and Late) were defined in the latest Lunar geologic time scale. The Moon is unique in the Solar System in that it is the only other body from which humans have rock samples with

38380-479: The topic, one supporting climate change, the other supporting human hunting as the primary cause of the extinctions. The hunting hypothesis suggests that humans hunted megaherbivores to extinction, which in turn caused the extinction of carnivores and scavengers which had preyed upon those animals. This hypothesis holds Pleistocene humans responsible for the megafaunal extinction. One variant, known as blitzkrieg , portrays this process as relatively quick. Some of

38582-535: The wave of extinctions in North America is the paleo-American culture associated with the Clovis people ( q.v. ), who were thought to use spear throwers to kill large animals. The chief criticism of the "prehistoric overkill hypothesis" has been that the human population at the time was too small and/or not sufficiently widespread geographically to have been capable of such ecologically significant impacts. This criticism does not mean that climate change scenarios explaining

38784-475: The wild, existing within only 9% of their historic range. Human pressures are to blame for the cheetah population crash, including prey loss due to overhunting by people, retaliatory killing from farmers, habitat loss and the illegal wildlife trade. Populations of brown bears have experienced similar population decline. The term pollinator decline refers to the reduction in abundance of insect and other animal pollinators in many ecosystems worldwide beginning at

38986-526: The work of James Hutton (1726–1797), in particular his Theory of the Earth , first presented before the Royal Society of Edinburgh in 1785. Hutton's theory would later become known as uniformitarianism , popularised by John Playfair (1748–1819) and later Charles Lyell (1797–1875) in his Principles of Geology . Their theories strongly contested the 6,000 year age of the Earth as suggested determined by James Ussher via Biblical chronology that

39188-404: The world. Although there is debate regarding how much human predation and habitat loss affected their decline, certain population declines have been directly correlated with the onset of human activity, such as the extinction events of New Zealand , Madagascar, and Hawaii . Aside from humans, climate change may have been a driving factor in the megafaunal extinctions, especially at the end of

39390-643: The world. The direct killing of megafauna for meat and body parts is the primary driver of their destruction, with 70% of the 362 megafauna species in decline as of 2019. Mammals in particular have suffered such severe losses as the result of human activity (mainly during the Quaternary extinction event , but partly during the Holocene) that it could take several million years for them to recover. Contemporary assessments have discovered that roughly 41% of amphibians, 25% of mammals, 21% of reptiles and 14% of birds are threatened with extinction, which could disrupt ecosystems on

39592-429: Was accepted at the time by western religion. Instead, using geological evidence, they contested Earth to be much older, cementing the concept of deep time. During the early 19th century William Smith , Georges Cuvier , Jean d'Omalius d'Halloy , and Alexandre Brongniart pioneered the systematic division of rocks by stratigraphy and fossil assemblages. These geologists began to use the local names given to rock units in

39794-447: Was estimated in 2012 that 13% of Earth's ice-free land surface is used as row-crop agricultural sites, 26% used as pastures, and 4% urban-industrial areas. In March 2019, Nature Climate Change published a study by ecologists from Yale University , who found that over the next half century, human land use will reduce the habitats of 1,700 species by up to 50%, pushing them closer to extinction. That same month PLOS Biology published

39996-415: Was in some places unwise, scholars such as Girolamo Fracastoro shared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd. Niels Stensen, more commonly known as Nicolas Steno (1638–1686), is credited with establishing four of the guiding principles of stratigraphy. In De solido intra solidum naturaliter contento dissertationis prodromus Steno states: Respectively, these are

40198-616: Was no continent-wide extinction of bison at the end of the Pleistocene (although the genus was regionally extirpated in many areas). The survival of bison into the Holocene and recent times is therefore inconsistent with the overkill scenario. By the end of the Pleistocene, when humans first entered North America, these large animals had been geographically separated from intensive human hunting for more than 200,000 years. Given this enormous span of geologic time, bison would almost certainly have been very nearly as naive as native North American large mammals. The culture that has been connected with

40400-535: Was not until the Italian Renaissance when Leonardo da Vinci (1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge': Of the stupidity and ignorance of those who imagine that these creatures were carried to such places distant from the sea by the Deluge...Why do we find so many fragments and whole shells between

40602-476: Was the last commercial publication of an international chronostratigraphic chart that was closely associated with the ICS. It included a proposal to substantially revise the pre-Cryogenian time scale to reflect important events such as the formation of the Solar System and the Great Oxidation Event , among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for

40804-496: Was unavailable because of shifts in the growing season). In contrast, small mammals, with their shorter life cycles , shorter reproductive cycles , and shorter gestation periods, could have adjusted to the increased unpredictability of the climate, both as individuals and as species which allowed them to synchronize their reproductive efforts with conditions favorable for offspring survival. If so, smaller mammals would have lost fewer offspring and would have been better able to repeat

#794205