123-481: [REDACTED] Look up impactor in Wiktionary, the free dictionary. Impactor may refer to: A large meteoroid, asteroid, comet, or other celestial object which causes an impact event Impactor ( Transformers ) , a fictional character Impactor (spacecraft) , a craft designed for high-velocity landing Impact wrench , a power tool IMPACTors, former name of
246-507: A predatory microorganism invaded a large prokaryote, probably an archaean , but instead of killing its prey, the attacker took up residence and evolved into mitochondria; one of these chimeras later tried to swallow a photosynthesizing cyanobacterium, but the victim survived inside the attacker and the new combination became the ancestor of plants ; and so on. After each endosymbiosis, the partners eventually eliminated unproductive duplication of genetic functions by re-arranging their genomes,
369-633: A 1 km (0.62 mi) diameter strike Earth every 500,000 years on average. Large collisions – with 5 km (3 mi) objects – happen approximately once every twenty million years. The last known impact of an object of 10 km (6 mi) or more in diameter was at the Cretaceous–Paleogene extinction event 66 million years ago. The energy released by an impactor depends on diameter, density, velocity, and angle. The diameter of most near-Earth asteroids that have not been studied by radar or infrared can generally only be estimated within about
492-493: A Nemesis-style periodicity. An impact event is commonly seen as a scenario that would bring about the end of civilization . In 2000, Discover magazine published a list of 20 possible sudden doomsday scenarios with an impact event listed as the most likely to occur. A joint Pew Research Center / Smithsonian survey from April 21 to 26, 2010 found that 31 percent of Americans believed that an asteroid will collide with Earth by 2050. A majority (61 percent) disagreed. In
615-446: A compartment for abiogenic processes. A genomic analysis supports this hypothesis as they found 355 genes that likely traced to LUCA upon 6.1 million sequenced prokaryotic genes. They reconstruct LUCA as a thermophilic anaerobe with a Wood-Ljungdahl pathway, implying an origin of life at white smokers. LUCA would also have exhibited other biochemical pathways such as gluconeogenesis , reverse incomplete Krebs cycle , glycolysis , and
738-519: A devastating asteroid], but we're not 100 percent certain when." Also in 2018, physicist Stephen Hawking considered in his final book Brief Answers to the Big Questions that an asteroid collision was the biggest threat to the planet. In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released
861-514: A diameter of 20 m (66 ft), and which strike Earth approximately twice every century, produce more powerful airbursts. The 2013 Chelyabinsk meteor was estimated to be about 20 m in diameter with an airburst of around 500 kilotons, an explosion 30 times the Hiroshima bomb impact. Much larger objects may impact the solid earth and create a crater. Objects with a diameter less than 1 m (3.3 ft) are called meteoroids and seldom make it to
984-444: A diameter of 4 meters (13 ft) enter Earth's atmosphere about once a year. Asteroids with a diameter of 7 meters enter the atmosphere about every 5 years with as much kinetic energy as the atomic bomb dropped on Hiroshima (approximately 16 kilotons of TNT), but the air burst is reduced to just 5 kilotons. These ordinarily explode in the upper atmosphere and most or all of the solids are vaporized . However, asteroids with
1107-399: A different scenario a single last universal ancestor, e.g. a "first cell" or a first individual precursor cell has never existed. Instead, the early biochemical evolution of life led to diversification through the development of a multiphenotypical population of pre-cells from which the precursor cells ( protocells ) of the three domains of life emerged. Thus, the formation of cells was
1230-526: A factor of two, by basing it on the asteroid's brightness. The density is generally assumed, because the diameter and mass, from which density can be calculated, are also generally estimated. Due to Earth's escape velocity , the minimum impact velocity is 11 km/s with asteroid impacts averaging around 17 km/s on the Earth. The most probable impact angle is 45 degrees. Impact conditions such as asteroid size and speed, but also density and impact angle determine
1353-613: A group of iron meteorites were found, estimated as dating to 4,000–5,000 years ago. It first came to attention of Spanish authorities in 1576; in 2015, police arrested four alleged smugglers trying to steal more than a ton of protected meteorites. The Henbury craters in Australia (~5,000 years old) and Kaali craters in Estonia (~2,700 years old) were apparently produced by objects that broke up before impact. Whitecourt crater in Alberta, Canada
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#17330935427041476-569: A hypothetical companion star to the Sun called Nemesis periodically disrupting the orbits of comets in the Oort cloud , leading to a large increase in the number of comets reaching the inner Solar System where they might hit Earth. Physicist Adrian Melott and paleontologist Richard Bambach have more recently verified the Raup and Sepkoski finding, but argue that it is not consistent with the characteristics expected of
1599-634: A left and a right side that are mirror images of each other, appeared by 555 Ma (million years ago). Ediacara biota appeared during the Ediacaran period, while vertebrates , along with most other modern phyla originated about 525 Ma during the Cambrian explosion . During the Permian period, synapsids , including the ancestors of mammals , dominated the land. The Permian–Triassic extinction event killed most complex species of its time, 252 Ma . During
1722-443: A long way to go, since theoretical and empirical approaches are only beginning to make contact with each other. Even the simplest members of the three modern domains of life use DNA to record their "recipes" and a complex array of RNA and protein molecules to "read" these instructions and use them for growth, maintenance and self-replication. The discovery that some RNA molecules can catalyze both their own replication and
1845-480: A particular environment rapidly becomes dominant; and they can catalyze the formation of RNA molecules. Although this idea has not become the scientific consensus, it still has active supporters. Research in 2003 reported that montmorillonite could also accelerate the conversion of fatty acids into "bubbles" and that the "bubbles" could encapsulate RNA attached to the clay. These "bubbles" can then grow by absorbing additional lipids and then divide. The formation of
1968-577: A process which sometimes involved transfer of genes between them. Another hypothesis proposes that mitochondria were originally sulfur - or hydrogen -metabolising endosymbionts, and became oxygen-consumers later. On the other hand, mitochondria might have been part of eukaryotes' original equipment. There is a debate about when eukaryotes first appeared: the presence of steranes in Australian shales may indicate eukaryotes at 2.7 Ga; however, an analysis in 2008 concluded that these chemicals infiltrated
2091-562: A significant role in the evolution of the Solar System since its formation. Major impact events have significantly shaped Earth's history , and have been implicated in the formation of the Earth–Moon system . Impact events also appear to have played a significant role in the evolutionary history of life . Impacts may have helped deliver the building blocks for life (the panspermia theory relies on this premise). Impacts have been suggested as
2214-409: A successive process. See § Metabolism first: Pre-cells, successive cellularisation , below. Life on Earth is based on carbon and water . Carbon provides stable frameworks for complex chemicals and can be easily extracted from the environment, especially from carbon dioxide . There is no other chemical element whose properties are similar enough to carbon's to be called an analogue; silicon ,
2337-533: A very small percentage of species have been identified: one estimate claims that Earth may have 1 trillion species, because "identifying every microbial species on Earth presents a huge challenge." Only 1.75–1.8 million species have been named and 1.8 million documented in a central database. The currently living species represent less than one percent of all species that have ever lived on Earth. The oldest meteorite fragments found on Earth are about 4.54 billion years old; this, coupled primarily with
2460-476: A volcanic origin, which has also been proposed as a cause for the iridium enrichment. Further, the chromium isotopic ratios measured in the K-T boundary are similar to the chromium isotopic ratios found in carbonaceous chondrites . Thus a probable candidate for the impactor is a carbonaceous asteroid, but a comet is also possible because comets are assumed to consist of material similar to carbonaceous chondrites. Probably
2583-458: A year. Such events would seem to be spectacularly obvious, but they generally go unnoticed for a number of reasons: the majority of the Earth's surface is covered by water; a good portion of the land surface is uninhabited; and the explosions generally occur at relatively high altitude, resulting in a huge flash and thunderclap but no real damage. Although no human is known to have been killed directly by an impact , over 1000 people were injured by
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#17330935427042706-446: Is a collision between astronomical objects causing measurable effects. Impact events have been found to regularly occur in planetary systems , though the most frequent involve asteroids , comets or meteoroids and have minimal effect. When large objects impact terrestrial planets such as the Earth , there can be significant physical and biospheric consequences, as the impacting body
2829-610: Is also coincidental to some of the earliest evidence of life on Earth, fossilized Stromatolites . Evidence for at least 4 impact events have been found in spherule layers (dubbed S1 through S8) from the Barberton Greenstone Belt in South Africa, spanning around 3.5-3.2 billion years ago. The sites of the impacts are thought to have been distant from the location of the belt. The impactors that generated these events are thought to have been much larger than those that created
2952-966: Is an excellent solvent and has two other useful properties: the fact that ice floats enables aquatic organisms to survive beneath it in winter; and its molecules have electrically negative and positive ends, which enables it to form a wider range of compounds than other solvents can. Other good solvents, such as ammonia , are liquid only at such low temperatures that chemical reactions may be too slow to sustain life, and lack water's other advantages. Organisms based on alternative biochemistry may, however, be possible on other planets. Research on how life might have emerged from non-living chemicals focuses on three possible starting points: self-replication , an organism's ability to produce offspring that are very similar to itself; metabolism, its ability to feed and repair itself; and external cell membranes , which allow food to enter and waste products to leave, but exclude unwanted substances. Research on abiogenesis still has
3075-520: Is estimated to be between 1,080 and 1,130 years old. The crater is approximately 36 m (118 ft) in diameter and 9 m (30 ft) deep, is heavily forested and was discovered in 2007 when a metal detector revealed fragments of meteoric iron scattered around the area. A Chinese record states that 10,000 people were killed in the 1490 Qingyang event with the deaths caused by a hail of "falling stones"; some astronomers hypothesize that this may describe an actual meteorite fall, although they find
3198-453: Is no definitive evidence of impacts leading to the three other major mass extinctions. In 1980, physicist Luis Alvarez ; his son, geologist Walter Alvarez ; and nuclear chemists Frank Asaro and Helen V. Michael from the University of California, Berkeley discovered unusually high concentrations of iridium in a specific layer of rock strata in the Earth's crust. Iridium is an element that
3321-496: Is normally associated with large impact events or atomic bomb explosions, has also been found in the same layer at more than 30 sites. Soot and ash at levels tens of thousands times normal levels were found with the above. Anomalies in chromium isotopic ratios found within the K-T boundary layer strongly support the impact theory. Chromium isotopic ratios are homogeneous within the earth, and therefore these isotopic anomalies exclude
3444-506: Is now Western Australia ), dated at more than 2.2 billion years ago with the impactor estimated to be around 7 kilometres (4.3 mi) wide. It is believed that, at this time, the Earth was mostly or completely frozen, commonly called the Huronian glaciation . The Vredefort impact event , which occurred around 2 billion years ago in Kaapvaal Craton (what is now South Africa ), caused
3567-546: Is rare on Earth but relatively abundant in many meteorites. From the amount and distribution of iridium present in the 65-million-year-old "iridium layer", the Alvarez team later estimated that an asteroid of 10 to 14 km (6 to 9 mi) must have collided with Earth. This iridium layer at the Cretaceous–Paleogene boundary has been found worldwide at 100 different sites. Multidirectionally shocked quartz (coesite), which
3690-446: Is sequestered into calcium carbonate ( calcite ), phosphate concentrations are able to increase to levels necessary for facilitating biomolecule creation. Though carbonate-rich lakes have alkaline chemistry in modern times, models suggest that carbonate lakes had a pH low enough for prebiotic synthesis when placed in the acidifying context of Earth's early carbon dioxide rich atmosphere . Rainwater rich in carbonic acid weathered
3813-477: Is shown in the adjacent figure, where important evolutionary improvements are indicated by numbers. Wet-dry cycles at geothermal springs are shown to solve the problem of hydrolysis and promote the polymerization and vesicle encapsulation of biopolymers. The temperatures of geothermal springs are suitable for biomolecules. Silica minerals and metal sulfides in these environments have photocatalytic properties to catalyze biomolecules. Solar UV exposure also promotes
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3936-402: Is solved in carbonate -rich environments. When in the presence of carbonate, calcium readily reacts to form calcium carbonate instead of apatite minerals. With the free calcium ions removed from solution , phosphate ions are no longer precipitated from solution. This is specifically seen in lakes with no inflow, since no new calcium is introduced into the water body. After all of the calcium
4059-405: Is that the Earth and Moon started to coalesce at the same time but the Earth, having a much stronger gravity than the early Moon, attracted almost all the iron particles in the area. Until 2001, the oldest rocks found on Earth were about 3.8 billion years old, leading scientists to estimate that the Earth's surface had been molten until then. Accordingly, they named this part of Earth's history
4182-476: Is usually traveling at several kilometres a second (a minimum of 11.2 km/s (7.0 mi/s) for an Earth impacting body ), though atmospheres mitigate many surface impacts through atmospheric entry . Impact craters and structures are dominant landforms on many of the Solar System 's solid objects and present the strongest empirical evidence for their frequency and scale. Impact events appear to have played
4305-398: Is water, which is much more plentiful than the geologically produced reducing agents required by the earlier non-oxygenic photosynthesis. From this point onwards life itself produced significantly more of the resources it needed than did geochemical processes. Oxygen became a significant component of Earth's atmosphere about 2.4 Ga. Although eukaryotes may have been present much earlier,
4428-410: The Cretaceous–Paleogene extinction event . Small objects frequently collide with Earth. There is an inverse relationship between the size of the object and the frequency of such events. The lunar cratering record shows that the frequency of impacts decreases as approximately the cube of the resulting crater's diameter, which is on average proportional to the diameter of the impactor. Asteroids with
4551-469: The Deccan Traps . While numerous impact craters have been confirmed on land or in the shallow seas over continental shelves , no impact craters in the deep ocean have been widely accepted by the scientific community. Impacts of projectiles as large as one km in diameter are generally thought to explode before reaching the sea floor, but it is unknown what would happen if a much larger impactor struck
4674-510: The Hadean . However, analysis of zircons formed 4.4 Ga indicates that Earth's crust solidified about 100 million years after the planet's formation and that the planet quickly acquired oceans and an atmosphere , which may have been capable of supporting life. Evidence from the Moon indicates that from 4 to 3.8 Ga it suffered a Late Heavy Bombardment by debris that was left over from the formation of
4797-691: The Lonar crater lake in India, approximately 52,000 years old (though a study published in 2010 gives a much greater age), which now has a flourishing semi-tropical jungle around it. The Rio Cuarto craters in Argentina were produced approximately 10,000 years ago, at the beginning of the Holocene. If proved to be impact craters, they would be the first impact of the Holocene. The Campo del Cielo ("Field of Heaven") refers to an area bordering Argentina's Chaco Province where
4920-626: The Solar System , and the Earth should have experienced an even heavier bombardment due to its stronger gravity. While there is no direct evidence of conditions on Earth 4 to 3.8 Ga, there is no reason to think that the Earth was not also affected by this late heavy bombardment. This event may well have stripped away any previous atmosphere and oceans; in this case gases and water from comet impacts may have contributed to their replacement, although outgassing from volcanoes on Earth would have supplied at least half. However, if subsurface microbial life had evolved by this point, it would have survived
5043-588: The domain Archea and finally to the domain Eucarya . For the development of cells ( cellularisation ), the pre-cells had to be protected from their surroundings by envelopes (i.e. membranes, walls). For instance, the development of rigid cell walls by the invention of peptidoglycan in bacteria (domain Bacteria) may have been a prerequisite for their successful survival, radiation and colonisation of virtually all habitats of
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5166-412: The dynamo mechanism at a planet's core responsible for maintaining the magnetic field of the planet , and may have contributed to Mars' lack of current magnetic field. An impact event may cause a mantle plume ( volcanism ) at the antipodal point of the impact. The Chicxulub impact may have increased volcanism at mid-ocean ridges and has been proposed to have triggered flood basalt volcanism at
5289-477: The endosymbiont mitochondria provided a more abundant source of biological energy . Around 1.6 Ga, some eukaryotes gained the ability to photosynthesize via endosymbiosis with cyanobacteria, and gave rise to various algae that eventually overtook cyanobacteria as the dominant primary producers . At around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions. While early organisms reproduced asexually ,
5412-610: The origin of water on Earth . They have also been implicated in several mass extinctions . The prehistoric Chicxulub impact , 66 million years ago, is believed to not only be the cause of the Cretaceous–Paleogene extinction event but acceleration of the evolution of mammals , leading to their dominance and, in turn, setting in place conditions for the eventual rise of humans . Throughout recorded history, hundreds of Earth impacts (and exploding bolides ) have been reported, with some occurrences causing deaths, injuries, property damage, or other significant localised consequences. One of
5535-508: The pentose phosphate pathway , including biochemical reactions such as reductive amination and transamination . The Panspermia hypothesis does not explain how life arose originally, but simply examines the possibility of its coming from somewhere other than Earth. The idea that life on Earth was "seeded" from elsewhere in the Universe dates back at least to the Greek philosopher Anaximander in
5658-593: The "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare. According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched. On 26 September 2022, the Double Asteroid Redirection Test demonstrated the deflection of an asteroid. It was the first such experiment to be carried out by humankind and
5781-483: The Chelyabinsk meteor airburst event over Russia in 2013. In 2005 it was estimated that the chance of a single person born today dying due to an impact is around 1 in 200,000. The two to four-meter-sized asteroids 2008 TC 3 , 2014 AA , 2018 LA , 2019 MO , 2022 EB5 , and the suspected artificial satellite WT1190F are the only known objects to be detected before impacting the Earth. Impacts have had, during
5904-505: The Cretaceous–Paleogene extinction event, scientists believe that the impactor was a metallic asteroid with a diameter in the order of 1.5 kilometres (0.9 mi). The impact would have had global effects. Artifacts recovered with tektites from the 803,000-year-old Australasian strewnfield event in Asia link a Homo erectus population to a significant meteorite impact and its aftermath. Significant examples of Pleistocene impacts include
6027-596: The Earth in the Sikhote-Alin Mountains , Primorye , Soviet Union. It was during daytime hours and was witnessed by many people, which allowed V. G. Fesenkov , then chairman of the meteorite committee of the USSR Academy of Science, to estimate the meteoroid's orbit before it encountered the Earth. Sikhote-Alin is a massive fall with the overall size of the meteoroid estimated at 90,000 kg (200,000 lb). A more recent estimate by Tsvetkov (and others) puts
6150-539: The Earth's closest celestial partner, the Moon, astrogeologists have determined that during the last 600 million years, the Earth has been struck by 60 objects of a diameter of 5 km (3 mi) or more. The smallest of these impactors would leave a crater almost 100 km (60 mi) across. Only three confirmed craters from that time period with that size or greater have been found: Chicxulub , Popigai , and Manicouagan , and all three have been suspected of being linked to extinction events though only Chicxulub,
6273-497: The Earth's crust pose significant challenges to conclusively identifying impacts from this period. Only two pieces of pristine lithosphere are believed to remain from this era: Kaapvaal Craton (in contemporary South Africa) and Pilbara Craton (in contemporary Western Australia) to search within which may potentially reveal evidence in the form of physical craters. Other methods may be used to identify impacts from this period, for example, indirect gravitational or magnetic analysis of
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#17330935427046396-503: The Earth's surface, a theory known as exogenesis . These modified views of Earth's history did not emerge until relatively recently, chiefly due to a lack of direct observations and the difficulty in recognizing the signs of an Earth impact because of erosion and weathering. Large-scale terrestrial impacts of the sort that produced the Barringer Crater , locally known as Meteor Crater , east of Flagstaff, Arizona, are rare. Instead, it
6519-455: The Japanese band IMP. See also [ edit ] [REDACTED] Search for "impactor" or "impactors" on Misplaced Pages. All pages with titles beginning with Impactor All pages with titles containing Impactor Impact (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with
6642-678: The Moon's origin is the giant impact theory, which postulates that Earth was once hit by a planetoid the size of Mars; such a theory is able to explain the size and composition of the Moon, something not done by other theories of lunar formation. According to the theory of the Late Heavy Bombardment , there should have been 22,000 or more impact craters with diameters >20 km (12 mi), about 40 impact basins with diameters about 1,000 km (620 mi), and several impact basins with diameters about 5,000 km (3,100 mi). However, hundreds of millions of years of deformation at
6765-630: The Permian-Triassic extinction is still a matter of debate; the age and origin of proposed impact craters, i.e. the Bedout High structure, hypothesized to be associated with it are still controversial. The last such mass extinction led to the demise of the non-avian dinosaurs and coincided with a large meteorite impact; this is the Cretaceous–Paleogene extinction event (also known as the K–T or K–Pg extinction event), which occurred 66 million years ago. There
6888-437: The Solar System was found to be cratered, and there was no reason to believe that the Earth had somehow escaped bombardment from space. In the last few decades of the 20th century, a large number of highly modified impact craters began to be identified. The first direct observation of a major impact event occurred in 1994: the collision of the comet Shoemaker-Levy 9 with Jupiter . Based on crater formation rates determined from
7011-415: The ability to tolerate and then to use oxygen, possibly via endosymbiosis , where one organism lives inside another and both of them benefit from their association. Cyanobacteria have the most complete biochemical "toolkits" of all the mat-forming organisms. Hence they are the most self-sufficient, well-adapted to strike out on their own both as floating mats and as the first of the phytoplankton , provide
7134-762: The assembly of vesicles. Exergonic reactions at hydrothermal vents are suggested to have been a source of free energy that promoted chemical reactions, synthesis of organic molecules, and are inducive to chemical gradients. In small rock pore systems, membranous structures between alkaline seawater and the acidic ocean would be conducive to natural proton gradients. Nucleobase synthesis could occur by following universally conserved biochemical pathways by using metal ions as catalysts. RNA molecules of 22 bases can be polymerized in alkaline hydrothermal vent pores. Thin pores are shown to only accumulate long polynucleotides whereas thick pores accumulate both short and long polynucleotides. Small mineral cavities or mineral gels could have been
7257-496: The atmosphere, leading to the Great Oxygenation Event around 2.4 Ga. The earliest evidence of eukaryotes (complex cells with organelles ) dates from 1.85 Ga, likely due to symbiogenesis between anaerobic archaea and aerobic proteobacteria in co-adaptation against the new oxidative stress . While eukaryotes may have been present earlier, their diversification accelerated when aerobic cellular respiration by
7380-428: The basis of most marine food chains. Eukaryotes may have been present long before the oxygenation of the atmosphere, but most modern eukaryotes require oxygen, which is used by their mitochondria to fuel the production of ATP , the internal energy supply of all known cells. In the 1970s, a vigorous debate concluded that eukaryotes emerged as a result of a sequence of endosymbiosis between prokaryotes . For example:
7503-619: The best-known recorded events in modern times was the Tunguska event , which occurred in Siberia , Russia, in 1908. The 2013 Chelyabinsk meteor event is the only known such incident in modern times to result in numerous injuries. Its meteor is the largest recorded object to have encountered the Earth since the Tunguska event. The Comet Shoemaker–Levy 9 impact provided the first direct observation of an extraterrestrial collision of Solar System objects, when
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#17330935427047626-417: The best-known recorded impacts in modern times was the Tunguska event, which occurred in Siberia , Russia, in 1908. This incident involved an explosion that was probably caused by the airburst of an asteroid or comet 5 to 10 km (3.1 to 6.2 mi) above the Earth's surface, felling an estimated 80 million trees over 2,150 km (830 sq mi). In February 1947, another large bolide impacted
7749-590: The biosphere has been the subject of scientific debate. Several theories of impact-related mass extinction have been developed. In the past 500 million years there have been five generally accepted major mass extinctions that on average extinguished half of all species . One of the largest mass extinctions to have affected life on Earth was the Permian-Triassic , which ended the Permian period 250 million years ago and killed off 90 percent of all species; life on Earth took 30 million years to recover. The cause of
7872-464: The bombardment. The earliest identified organisms were minute and relatively featureless, and their fossils looked like small rods that are very difficult to tell apart from structures that arise through abiotic physical processes. The oldest undisputed evidence of life on Earth, interpreted as fossilized bacteria, dates to 3 Ga. Other finds in rocks dated to about 3.5 Ga have been interpreted as bacteria, with geochemical evidence also seeming to show
7995-427: The bottom layer is oxygen-free and often dominated by hydrogen sulfide emitted by the organisms living there. Oxygen is toxic to organisms that are not adapted to it, but greatly increases the metabolic efficiency of oxygen-adapted organisms; oxygenic photosynthesis by bacteria in mats increased biological productivity by a factor of between 100 and 1,000. The source of hydrogen atoms used by oxygenic photosynthesis
8118-574: The capabilities of individual organisms. Ribozymes remain as the main components of ribosomes , the "protein factories" in modern cells. Evidence suggests the first RNA molecules formed on Earth prior to 4.17 Ga. Although short self-replicating RNA molecules have been artificially produced in laboratories, doubts have been raised about whether natural non-biological synthesis of RNA is possible. The earliest "ribozymes" may have been formed of simpler nucleic acids such as PNA , TNA or GNA , which would have been replaced later by RNA. In 2003, it
8241-556: The comet broke apart and collided with Jupiter in July 1994. An extrasolar impact was observed in 2013, when a massive terrestrial planet impact was detected around the star ID8 in the star cluster NGC 2547 by NASA's Spitzer Space Telescope and confirmed by ground observations. Impact events have been a plot and background element in science fiction . In April 2018, the B612 Foundation reported: "It's 100 percent certain we'll be hit [by
8364-534: The construction of proteins led to the hypothesis of earlier life-forms based entirely on RNA. These ribozymes could have formed an RNA world in which there were individuals but no species, as mutations and horizontal gene transfers would have meant that offspring were likely to have different genomes from their parents, and evolution occurred at the level of genes rather than organisms. RNA would later have been replaced by DNA, which can build longer, more stable genomes, strengthening heritability and expanding
8487-624: The continuous exposure to sunlight as well as their cell walls with ion pumps to maintain their intracellular metabolism after they entered the oceans. Catalytic mineral particles and transition metal sulfides at these environments are capable of catalyzing organic compounds. Scientists simulated laboratory conditions that were identical to white smokers and successfully oligomerized RNA, measured to be 4 units long. Long chain fatty acids can be synthesized via Fischer-Tropsch synthesis . Another experiment that replicated conditions also similar white smokers, with long chain fatty acids present resulted in
8610-479: The cytoplasm of modern cells. Fatty acids in acidic or slightly alkaline geothermal springs assemble into vesicles after wet-dry cycles as there is a lower concentration of ionic solutes at geothermal springs since they are freshwater environments, in contrast to seawater which has a higher concentration of ionic solutes. For organic compounds to be present at geothermal springs, they would have likely been transported by carbonaceous meteors. The molecules that fell from
8733-416: The dating of ancient lead deposits, has put the estimated age of Earth at around that time. The Moon has the same composition as Earth's crust but does not contain an iron -rich core like the Earth's. Many scientists think that about 40 million years after the formation of Earth, it collided with a body the size of Mars , throwing crust material into the orbit that formed the Moon. Another hypothesis
8856-576: The deep ocean. The lack of a crater, however, does not mean that an ocean impact would not have dangerous implications for humanity. Some scholars have argued that an impact event in an ocean or sea may create a megatsunami , which can cause destruction both at sea and on land along the coast, but this is disputed. The Eltanin impact into the Pacific Ocean 2.5 Mya is thought to involve an object about 1 to 4 kilometres (0.62 to 2.49 mi) across but remains craterless. The effect of impact events on
8979-461: The development of a multiphenotypical population of pre-cells , i.e. evolving entities of primordial life with different characteristics and widespread horizontal gene transfer . From this pre-cell population the founder groups A, B, C and then, from them, the precursor cells (here named proto-cells) of the three domains of life arose successively, leading first to the domain Bacteria , then to
9102-404: The dominant form of life in the early Archean eon, and many of the major steps in early evolution are thought to have taken place in this environment. The evolution of photosynthesis by cyanobacteria , around 3.5 Ga, eventually led to a buildup of its waste product, oxygen , in the oceans. After free oxygen saturated all available reductant substances on the Earth's surface , it built up in
9225-746: The earliest terrestrial ecosystems at least 2.7 Ga, the evolution of plants from freshwater green algae dates back to about 1 billion years ago. Microorganisms are thought to have paved the way for the inception of land plants in the Ordovician period. Land plants were so successful that they are thought to have contributed to the Late Devonian extinction event as early tree Archaeopteris drew down CO 2 levels, leading to global cooling and lowered sea levels, while their roots increased rock weathering and nutrient run-offs which may have triggered algal bloom anoxic events . Bilateria , animals having
9348-451: The earliest cells may have been aided by similar processes. A similar hypothesis presents self-replicating iron-rich clays as the progenitors of nucleotides , lipids and amino acids . A series of experiments starting in 1997 showed that early stages in the formation of proteins from inorganic materials including carbon monoxide and hydrogen sulfide could be achieved by using iron sulfide and nickel sulfide as catalysts . Most of
9471-469: The early history of the Earth (about four billion years ago), bolide impacts were almost certainly common since the Solar System contained far more discrete bodies than at present. Such impacts could have included strikes by asteroids hundreds of kilometers in diameter, with explosions so powerful that they vaporized all the Earth's oceans. It was not until this heavy bombardment slackened that life appears to have begun to evolve on Earth. The leading theory of
9594-481: The element directly below carbon on the periodic table , does not form very many complex stable molecules, and because most of its compounds are water-insoluble and because silicon dioxide is a hard and abrasive solid in contrast to carbon dioxide at temperatures associated with living things, it would be more difficult for organisms to extract. The elements boron and phosphorus have more complex chemistries but suffer from other limitations relative to carbon. Water
9717-498: The external membranes of cells may have been an essential first step. Experiments that simulated the conditions of the early Earth have reported the formation of lipids, and these can spontaneously form liposomes , double-walled "bubbles", and then reproduce themselves. Although they are not intrinsically information-carriers as nucleic acids are, they would be subject to natural selection for longevity and reproduction. Nucleic acids such as RNA might then have formed more easily within
9840-484: The form of fossilized microorganisms in hydrothermal vent precipitates from the Nuvvuagittuq Belt , that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and after the Earth formed 4.54 billion years ago. These earliest fossils, however, may have originated from non-biological processes. Microbial mats of coexisting bacteria and archaea were
9963-467: The geosphere and hydrosphere. This scenario may explain the quasi-random distribution of evolutionarily important features among the three domains and, at the same time, the existence of the most basic biochemical features (genetic code, set of protein amino acids etc.) in all three domains (unity of life), as well as the close relationship between the Archaea and the Eucarya. A scheme of the pre-cell scenario
10086-647: The globe. Two 10-kilometre sized (6.2 mi) asteroids are now believed to have struck Australia between 360 and 300 million years ago at the Western Warburton and East Warburton Basins , creating a 400-kilometre impact zone (250 mi). According to evidence found in 2015, it is the largest ever recorded. A third, possible impact was also identified in 2015 to the north, on the upper Diamantina River , also believed to have been caused by an asteroid 10 km across about 300 million years ago, but further studies are needed to establish that this crustal anomaly
10209-449: The ground to become meteorites. An estimated 500 meteorites reach the surface each year, but only 5 or 6 of these typically create a weather radar signature with a strewn field large enough to be recovered and be made known to scientists. The late Eugene Shoemaker of the U.S. Geological Survey estimated the rate of Earth impacts, concluding that an event about the size of the nuclear weapon that destroyed Hiroshima occurs about once
10332-495: The history of the Earth, a significant geological and climatic influence. The Moon 's existence is widely attributed to a huge impact early in Earth's history . Impact events earlier in the history of Earth have been credited with creative as well as destructive events; it has been proposed that impacting comets delivered the Earth's water, and some have suggested that the origins of life may have been influenced by impacting objects by bringing organic chemicals or lifeforms to
10455-599: The kinetic energy released in an impact event. The more energy is released, the more damage is likely to occur on the ground due to the environmental effects triggered by the impact. Such effects can be shock waves, heat radiation, the formation of craters with associated earthquakes, and tsunamis if bodies of water are hit. Human populations are vulnerable to these effects if they live within the affected zone. Large seiche waves arising from earthquakes and large-scale deposit of debris can also occur within minutes of impact, thousands of kilometres from impact. Stony asteroids with
10578-669: The lake - allowing the first prebiotic syntheses on Earth to occur. Microbial mats are multi-layered, multi-species colonies of bacteria and other organisms that are generally only a few millimeters thick, but still contain a wide range of chemical environments, each of which favors a different set of microorganisms. To some extent each mat forms its own food chain , as the by-products of each group of microorganisms generally serve as "food" for adjacent groups. Stromatolites are stubby pillars built as microorganisms in mats slowly migrate upwards to avoid being smothered by sediment deposited on them by water. There has been vigorous debate about
10701-462: The largest known still existing craters/impact structures on Earth, with the impactors having estimated diameters of ~20–50 kilometres (12–31 mi), with the craters generated by these impacts having an estimated diameter of 400–1,000 kilometres (250–620 mi). The largest impacts like those represented by the S2 layer are likely to have had far-reaching effects, such as the boiling of the surface layer of
10824-404: The largest of the three, has been consistently considered. The impact that caused Mistastin crater generated temperatures exceeding 2,370 °C, the highest known to have occurred on the surface of the Earth. Besides the direct effect of asteroid impacts on a planet's surface topography, global climate and life, recent studies have shown that several consecutive impacts might have an effect on
10947-475: The largest verified crater, a multi-ringed structure 160–300 km (100–200 mi) across, forming from an impactor approximately 10–15 km (6.2–9.3 mi) in diameter. The Sudbury impact event occurred on the Nuna supercontinent (now Canada ) from a bolide approximately 10–15 km (6.2–9.3 mi) in diameter approximately 1.849 billion years ago Debris from the event would have been scattered across
11070-420: The liposomes than outside. RNA is complex and there are doubts about whether it can be produced non-biologically in the wild. Some clays , notably montmorillonite , have properties that make them plausible accelerators for the emergence of an RNA world: they grow by self-replication of their crystalline pattern; they are subject to an analogue of natural selection, as the clay "species" that grows fastest in
11193-427: The mantle, but may prove inconclusive. In 2021, evidence for a probable impact 3.46 billion-years ago at Pilbara Craton has been found in the form of a 150 kilometres (93 mi) crater created by the impact of a 10 kilometres (6.2 mi) asteroid (named "The Apex Asteroid") into the sea at a depth of 2.5 kilometres (1.6 mi) (near the site of Marble Bar, Western Australia ). The event caused global tsunamis. It
11316-528: The mass at around 100,000 kg (220,000 lb). It was an iron meteorite belonging to the chemical group IIAB and with a coarse octahedrite structure. More than 70 tonnes ( metric tons ) of material survived the collision. A case of a human injured by a space rock occurred on November 30, 1954, in Sylacauga, Alabama . There a 4 kg (8.8 lb) stone chondrite crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She
11439-406: The meteors were then accumulated in geothermal springs. Geothermal springs can accumulate aqueous phosphate in the form of phopshoric acid . Based on lab-run models, these concentrations of phoshate are insufficient to facilitate biosynthesis . As for the evolutionary implications, freshwater heterotrophic cells that depended upon synthesized organic compounds later evolved photosynthesis because of
11562-571: The most convincing evidence for a worldwide catastrophe was the discovery of the crater which has since been named Chicxulub Crater . This crater is centered on the Yucatán Peninsula of Mexico and was discovered by Tony Camargo and Glen Penfield while working as geophysicists for the Mexican oil company PEMEX . What they reported as a circular feature later turned out to be a crater estimated to be 180 km (110 mi) in diameter. This convinced
11685-496: The most credible sources are Mars and Venus ; by alien visitors , possibly as a result of accidental contamination by microorganisms that they brought with them; and from outside the Solar System but by natural means. Experiments in low Earth orbit, such as EXOSTACK , have demonstrated that some microorganism spores can survive the shock of being catapulted into space and some can survive exposure to outer space radiation for at least 5.7 years. Meteorite ALH84001 , which
11808-508: The number of deaths implausible. Kamil Crater , discovered from Google Earth image review in Egypt , 45 m (148 ft) in diameter and 10 m (33 ft) deep, is thought to have been formed less than 3,500 years ago in a then-unpopulated region of western Egypt. It was found February 19, 2009 by V. de Michelle on a Google Earth image of the East Uweinat Desert, Egypt. One of
11931-653: The oceans. The Maniitsoq structure , dated to around 3 billion years old (3 Ga), was once thought to be the result of an impact; however, follow-up studies have not confirmed its nature as an impact structure. The Maniitsoq structure is not recognised as an impact structure by the Earth Impact Database . In 2020, scientists discovered the world's oldest confirmed impact crater, the Yarrabubba crater , caused by an impact that occurred in Yilgarn Craton (what
12054-601: The origin of life since it is a critical component of nucleotides , phospholipids , and adenosine triphosphate . Phosphate is often depleted in natural environments due to its uptake by microbes and its affinity for calcium ions. In a process called ' apatite precipitation', free phosphate ions react with the calcium ions abundant in water to precipitate out of solution as apatite minerals. When attempting to simulate prebiotic phosphorylation , scientists have only found success when using phosphorus levels far above modern day natural concentrations. This problem of low phosphate
12177-522: The origin of life. Similar to the process predicted by geothermal hot spring hypotheses , changing lake levels and wave action deposited phosphorus-rich brine onto dry shore and marginal pools. This drying of the solution promotes polymerization reactions and removes enough water to promote phosphorylation, a process integral to biological energy storage and transfer. When washed away by further precipitation and wave action, researchers concluded these newly formed biomolecules may have washed back into
12300-445: The oxygenation of the atmosphere was a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular organisms are built. The boundary between oxygen-rich and oxygen-free layers in microbial mats would have moved upwards when photosynthesis shut down overnight, and then downwards as it resumed on the next day. This would have created selection pressure for organisms in this intermediate zone to acquire
12423-537: The presence of life 3.8 Ga. However, these analyses were closely scrutinized, and non-biological processes were found which could produce all of the "signatures of life" that had been reported. While this does not prove that the structures found had a non-biological origin, they cannot be taken as clear evidence for the presence of life. Geochemical signatures from rocks deposited 3.4 Ga have been interpreted as evidence for life. Evidence for fossilized microorganisms considered to be 3.77 billion to 4.28 billion years old
12546-463: The primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants ), is sexual reproduction , the fusion of male and female reproductive cells ( gametes ) to create a zygote . The origin and evolution of sexual reproduction remain a puzzle for biologists, though it is thought to have evolved from a single-celled eukaryotic ancestor. While microorganisms formed
12669-486: The process of evolution from a common ancestor . The earliest clear evidence of life comes from biogenic carbon signatures and stromatolite fossils discovered in 3.7 billion-year-old metasedimentary rocks from western Greenland . In 2015, possible "remains of biotic life " were found in 4.1 billion-year-old rocks in Western Australia . There is further evidence of possibly the oldest forms of life in
12792-513: The recovery from this catastrophe, archosaurs became the most abundant land vertebrates; one archosaur group, the dinosaurs , dominated the Jurassic and Cretaceous periods. After the Cretaceous–Paleogene extinction event 66 Ma killed off the non-avian dinosaurs, mammals increased rapidly in size and diversity . Such mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. Only
12915-451: The result of impact events on solid objects and, as the dominant landforms on many of the System's solid objects, present the most solid evidence of prehistoric events. Notable impact events include the hypothesized Late Heavy Bombardment , which would have occurred early in the history of the Earth–Moon system, and the confirmed Chicxulub impact 66 million years ago, believed to be the cause of
13038-417: The rock on the surface of the Earth at rates far greater than today. With high phosphate influx, no phosphate precipitation, and no microbial usage of phosphate at this time, models show phosphate reached concentrations approximately 100 times greater than they are today. Modeled pH and phosphate levels of early Earth carbonate-rich lakes nearly match the conditions used in current laboratory experiments on
13161-438: The rocks less than 2.2 Ga and prove nothing about the origins of eukaryotes. Fossils of the algae Grypania have been reported in 1.85 billion-year-old rocks (originally dated to 2.1 Ga but later revised ), indicating that eukaryotes with organelles had already evolved. A diverse collection of fossil algae were found in rocks dated between 1.5 and 1.4 Ga. The earliest known fossils of fungi date from 1.43 Ga. Plastids ,
13284-437: The sixth century BCE . In the twentieth century it was proposed by the physical chemist Svante Arrhenius , by the astronomers Fred Hoyle and Chandra Wickramasinghe , and by molecular biologist Francis Crick and chemist Leslie Orgel . There are three main versions of the "seeded from elsewhere" hypothesis: from elsewhere in our Solar System via fragments knocked into space by a large meteor impact, in which case
13407-490: The size of the Chicxulub crater, which did not result in any mass extinctions, and there is no clear linkage between an impact and any other incident of mass extinction. Paleontologists David M. Raup and Jack Sepkoski have proposed that an excess of extinction events occurs roughly every 26 million years (though many are relatively minor). This led physicist Richard A. Muller to suggest that these extinctions could be due to
13530-423: The steps required temperatures of about 100 °C (212 °F) and moderate pressures, although one stage required 250 °C (482 °F) and a pressure equivalent to that found under 7 kilometres (4.3 mi) of rock. Hence it was suggested that self-sustaining synthesis of proteins could have occurred near hydrothermal vents. In this scenario, the biochemical evolution of life led to diversification through
13653-415: The superclass of organelles of which chloroplasts are the best-known exemplar, are thought to have originated from endosymbiotic cyanobacteria. The symbiosis evolved around 1.5 Ga and enabled eukaryotes to carry out oxygenic photosynthesis . Three evolutionary lineages of photosynthetic plastids have since emerged: chloroplasts in green algae and plants, rhodoplasts in red algae and cyanelles in
13776-407: The synthesis of biomolecules like RNA nucleotides. An analysis of hydrothermal veins at a 3.5 Gya (giga years ago or 1 billion years) geothermal spring setting were found to have elements required for the origin of life, which are potassium, boron, hydrogen, sulfur, phosphorus, zinc, nitrogen, and oxygen. Mulkidjanian and colleagues find that such environments have identical ionic concentrations to
13899-464: The title Impactor . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Impactor&oldid=1230813698 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Impact event An impact event
14022-400: The validity of alleged stromatolite fossils from before 3 Ga, with critics arguing that they could have been formed by non-biological processes. In 2006, another find of stromatolites was reported from the same part of Australia, in rocks dated to 3.5 Ga. In modern underwater mats the top layer often consists of photosynthesizing cyanobacteria which create an oxygen-rich environment, while
14145-535: The vast majority of scientists that this extinction resulted from a point event that is most probably an extraterrestrial impact and not from increased volcanism and climate change (which would spread its main effect over a much longer time period). Although there is now general agreement that there was a huge impact at the end of the Cretaceous that led to the iridium enrichment of the K-T boundary layer, remnants have been found of other, smaller impacts, some nearing half
14268-594: Was badly bruised by the fragments . Several persons have since claimed to have been struck by "meteorites" but no verifiable meteorites have resulted. Evolutionary history of life The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga , for gigaannum ) and evidence suggests that life emerged prior to 3.7 Ga. The similarities among all known present-day species indicate that they have diverged through
14391-427: Was considered to be highly successful. The orbital period of the target body was changed by 32 minutes. The criterion for success was a change of more than 73 seconds. Major impact events have significantly shaped Earth's history , having been implicated in the formation of the Earth–Moon system , the evolutionary history of life , the origin of water on Earth , and several mass extinctions . Impact structures are
14514-422: Was correctly identified as an impact crater, and it was not until as recently as 1963 that research by Eugene Merle Shoemaker conclusively proved this hypothesis. The findings of late 20th-century space exploration and the work of scientists such as Shoemaker demonstrated that impact cratering was by far the most widespread geological process at work on the Solar System's solid bodies. Every surveyed solid body in
14637-547: Was found in the Nuvvuagittuq Greenstone Belt in Quebec, Canada, although the evidence is disputed as inconclusive. Some biologists reason that all living organisms on Earth must share a single last universal ancestor , because it would be virtually impossible that two or more separate lineages could have independently developed the many complex biochemical mechanisms common to all living organisms. According to
14760-479: Was indeed the result of an impact event. The prehistoric Chicxulub impact , 66 million years ago, believed to be the cause of the Cretaceous–Paleogene extinction event, was caused by an asteroid estimated to be about 10 kilometres (6.2 mi) wide. Analysis of the Hiawatha Glacier reveals the presence of a 31 km wide impact crater dated at 58 million years of age, less than 10 million years after
14883-491: Was once part of the Martian crust, shows evidence of carbonate-globules with texture and size indicative of terrestrial bacterial activity. Scientists are divided over the likelihood of life arising independently on Mars, or on other planets in our galaxy . One theory traces the origins of life to the abundant carbonate-rich lakes which would have dotted the early Earth . Phosphate would have been an essential cornerstone to
15006-411: Was proposed that porous metal sulfide precipitates would assist RNA synthesis at about 100 °C (212 °F) and ocean-bottom pressures near hydrothermal vents . Under this hypothesis, lipid membranes would be the last major cell components to appear and, until then, the protocells would be confined to the pores. It has been suggested that double-walled "bubbles" of lipids like those that form
15129-469: Was widely thought that cratering was the result of volcanism : the Barringer Crater, for example, was ascribed to a prehistoric volcanic explosion (not an unreasonable hypothesis, given that the volcanic San Francisco Peaks stand only 48 km or 30 mi to the west). Similarly, the craters on the surface of the Moon were ascribed to volcanism. It was not until 1903–1905 that the Barringer Crater
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