144-470: An outfall is the discharge point of a waste stream into a body of water; alternatively it may be the outlet of a river , drain or a sewer where it discharges into the sea , a lake or ocean. In the United States, industrial facilities that discharge storm water which was exposed to industrial activities at the site are required to have a multi-sector general permit. Issuing permits for storm water
288-420: A double helix . The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides . Each nucleotide is composed of a nitrogen-containing nucleobase —either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a sugar called deoxyribose and a phosphate group . The nucleotides are joined to one another in a chain by covalent bonds between
432-582: A lake , an ocean , or another river. A stream refers to water that flows in a natural channel , a geographic feature that can contain flowing water. A stream may also be referred to as a watercourse. The study of the movement of water as it occurs on Earth is called hydrology , and their effect on the landscape is covered by geomorphology . Rivers are part of the water cycle , the continuous processes by which water moves about Earth. This means that all water that flows in rivers must ultimately come from precipitation . The sides of rivers have land that
576-420: A living systems theory viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this include Stuart Kauffman 's definition as an autonomous agent or a multi-agent system capable of reproducing itself, and of completing at least one thermodynamic work cycle . This definition
720-428: A nucleus and other membrane-bound organelles , although they have circular DNA and ribosomes . Bacteria and Archaea are two domains of prokaryotes. The other primary type is the eukaryote cell, which has a distinct nucleus bound by a nuclear membrane and membrane-bound organelles, including mitochondria , chloroplasts , lysosomes , rough and smooth endoplasmic reticulum , and vacuoles . In addition, their DNA
864-536: A trip hammer , and grind grains with a millstone . In the Middle Ages , water mills began to automate many aspects of manual labor , and spread rapidly. By 1300, there were at least 10,000 mills in England alone. A medieval watermill could do the work of 30–60 human workers. Water mills were often used in conjunction with dams to focus and increase the speed of the water. Water wheels continued to be used up to and through
1008-403: A universal common ancestor . This evolved into all the species that exist now, by way of many extinct species, some of which have left traces as fossils . Attempts to classify living things, too, began with Aristotle . Modern classification began with Carl Linnaeus 's system of binomial nomenclature in the 1740s. Living things are composed of biochemical molecules , formed mainly from
1152-715: A boat along certain stretches. In these religions, such as that of the Altai in Russia , the river is considered a living being that must be afforded respect. Rivers are some of the most sacred places in Hinduism. There is archeological evidence that mass ritual bathing in rivers at least 5,000 years ago in the Indus river valley . While most rivers in India are revered, the Ganges is most sacred. The river has
1296-515: A central role in various Hindu myths, and its water is said to have properties of healing as well as absolution from sins. Hindus believe that when the cremated remains of a person is released into the Ganges, their soul is released from the mortal world. Freshwater fish make up 40% of the world's fish species, but 20% of these species are known to have gone extinct in recent years. Human uses of rivers make these species especially vulnerable. Dams and other engineered changes to rivers can block
1440-407: A common origin. All life forms require certain core chemical elements for their biochemical functioning. These include carbon , hydrogen , nitrogen , oxygen , phosphorus , and sulfur —the elemental macronutrients for all organisms. Together these make up nucleic acids , proteins and lipids , the bulk of living matter. Five of these six elements comprise the chemical components of DNA,
1584-524: A consequence of these microbial activities, the physical-chemical environment on Earth has been changing on a geologic time scale , thereby affecting the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this posed novel evolutionary challenges, and ultimately resulted in
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#17330860418091728-408: A continuous flow of water throughout the year. This may be because an arid climate is too dry depending on the season to support a stream, or because a river is seasonally frozen in the winter (such as in an area with substantial permafrost ), or in the headwaters of rivers in mountains, where snowmelt is required to fuel the river. These rivers can appear in a variety of climates, and still provide
1872-656: A few core chemical elements . All living things contain two types of large molecule, proteins and nucleic acids , the latter usually both DNA and RNA : these carry the information needed by each species, including the instructions to make each type of protein. The proteins, in turn, serve as the machinery which carries out the many chemical processes of life. The cell is the structural and functional unit of life. Smaller organisms, including prokaryotes (bacteria and archaea ), consist of small single cells. Larger organisms , mainly eukaryotes , can consist of single cells or may be multicellular with more complex structure. Life
2016-564: A habitat for aquatic life and perform other ecological functions. Subterranean rivers may flow underground through flooded caves. This can happen in karst systems, where rock dissolves to form caves. These rivers provide a habitat for diverse microorganisms and have become an important target of study by microbiologists . Other rivers and streams have been covered over or converted to run in tunnels due to human development. These rivers do not typically host any life, and are often used only for stormwater or flood control. One such example
2160-442: A host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life , as it may support the hypothesis that life could have started as self-assembling organic molecules . Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles (430 BC) argued that everything in
2304-495: A large scale. This has been attributed to unusually large floods destroying infrastructure; however, there is evidence that permanent changes to climate causing higher aridity and lower river flow may have been the determining factor in what river civilizations succeeded or dissolved. Water wheels began to be used at least 2,000 years ago to harness the energy of rivers. Water wheels turn an axle that can supply rotational energy to move water into aqueducts , work metal using
2448-466: A lower elevation , such as an ocean , lake , or another river. A river may run dry before reaching the end of its course if it runs out of water, or only flow during certain seasons. Rivers are regulated by the water cycle , the processes by which water moves around the Earth. Water first enters rivers through precipitation , whether from rainfall, the runoff of water down a slope, the melting of glaciers or snow , or seepage from aquifers beneath
2592-466: A matter of debate; viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses have been classed into "species" based on their genetics , but many aspects of such a classification remain controversial. The original Linnaean system has been modified many times, for example as follows: The attempt to organise the Eukaryotes into
2736-526: A month in a simulated Martian environment . Beyond the Solar System, the region around another main-sequence star that could support Earth-like life on an Earth-like planet is known as the habitable zone . The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on
2880-548: A peak in the 1970s, when between two or three dams were completed every day, and has since begun to decline. New dam projects are primarily focused in China , India , and other areas in Asia . The first civilizations of Earth were born on floodplains between 5,500 and 3,500 years ago. The freshwater, fertile soil, and transportation provided by rivers helped create the conditions for complex societies to emerge. Three such civilizations were
3024-448: A resurgence of interest in the work of Russell, Barge and colleagues. Hylomorphism is a theory first expressed by the Greek philosopher Aristotle (322 BC). The application of hylomorphism to biology was important to Aristotle, and biology is extensively covered in his extant writings . In this view, everything in the material universe has both matter and form, and the form of a living thing
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#17330860418093168-866: A ritualistic sense has been compared to the Christian ritual of baptism , famously the Baptism of Jesus in the Jordan River . Floods also appear in Norse mythology , where the world is said to emerge from a void that eleven rivers flowed into. Aboriginal Australian religion and Mesoamerican mythology also have stories of floods, some of which contain no survivors, unlike the Abrahamic flood. Along with mythological rivers, religions have also cared for specific rivers as sacred rivers. The Ancient Celtic religion saw rivers as goddesses. The Nile had many gods attached to it. The tears of
3312-425: A river can take several forms. Tidal rivers (often part of an estuary ) have their levels rise and fall with the tide . Since the levels of these rivers are often already at or near sea level, the flow of alluvium and the brackish water that flows in these rivers may be either upriver or downriver depending on the time of day. Rivers that are not tidal may form deltas that continuously deposit alluvium into
3456-756: A river such as fish , aquatic plants , and insects have different roles, including processing organic matter and predation . Rivers have produced abundant resources for humans, including food , transportation , drinking water , and recreation. Humans have engineered rivers to prevent flooding, irrigate crops, perform work with water wheels , and produce hydroelectricity from dams. People associate rivers with life and fertility and have strong religious, political, social, and mythological attachments to them. Rivers and river ecosystems are threatened by water pollution , climate change , and human activity. The construction of dams, canals , levees , and other engineered structures has eliminated habitats, has caused
3600-460: A section of the river behind them into a lake or reservoir. This can provide nearby cities with a predictable supply of drinking water. Hydroelectricity is desirable as a form of renewable energy that does not require any inputs beyond the river itself. Dams are very common worldwide, with at least 75,000 higher than 6 feet (1.8 m) in the U.S. Globally, reservoirs created by dams cover 193,500 square miles (501,000 km ). Dam-building reached
3744-801: A set of 355 genes from the last universal common ancestor was tentatively identified. The biosphere is postulated to have developed, from the origin of life onwards, at least some 3.5 billion years ago. The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia . More recently, in 2015, "remains of biotic life " were found in 4.1 billion-year-old rocks in Western Australia. In 2017, putative fossilised microorganisms (or microfossils ) were announced to have been discovered in hydrothermal vent precipitates in
3888-605: A short period Linnaeus had classified them in the taxon Vermes in Animalia, but later placed them back in Plantae. Herbert Copeland classified the Fungi in his Protoctista , including them with single-celled organisms and thus partially avoiding the problem but acknowledging their special status. The problem was eventually solved by Whittaker , when he gave them their own kingdom in his five-kingdom system . Evolutionary history shows that
4032-462: A small number of kingdoms has been challenged. The Protozoa do not form a clade or natural grouping, and nor do the Chromista (Chromalveolata). The ability to sequence large numbers of complete genomes has allowed biologists to take a metagenomic view of the phylogeny of the whole tree of life . This has led to the realisation that the majority of living things are bacteria, and that all have
4176-408: A thousand years. In the late 1740s, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning. The fungi were originally treated as plants. For
4320-450: A water body from an outfall. An ocean outfall may be conveyed several miles offshore, to discharge by nozzles at the end of a spreader or T-shaped structure. Outfalls may also be constructed as an outfall tunnel or subsea tunnel and discharge effluent to the ocean via one or more marine risers with nozzles. River A river is a natural freshwater stream that flows on land or inside caves towards another body of water at
4464-438: A water body is that body's riparian zone . Plants in the riparian zone of a river help stabilize its banks to prevent erosion and filter alluvium deposited by the river on the shore, including processing the nitrogen and other nutrients it contains. Forests in a riparian zone also provide important animal habitats . River ecosystems have also been categorized based on the variety of aquatic life they can sustain, also known as
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4608-497: A water cycle that involved precipitation. The term flumen , in planetary geology , refers to channels on Saturn 's moon Titan that may carry liquid. Titan's rivers flow with liquid methane and ethane . There are river valleys that exhibit wave erosion , seas, and oceans. Scientists hope to study these systems to see how coasts erode without the influence of human activity, something that isn't possible when studying terrestrial rivers. Life Life on Earth: Life
4752-445: Is a tributary , and the place they meet is a confluence . Rivers must flow to lower altitudes due to gravity . The bed of a river is typically within a river valley between hills or mountains . Rivers flowing through an impermeable section of land such as rocks will erode the slopes on the sides of the river. When a river carves a plateau or a similar high-elevation area, a canyon can form, with cliffs on either side of
4896-473: Is a mechanistic explanation for the origin of species by means of natural selection . At the beginning of the 20th century Stéphane Leduc (1853–1939) promoted the idea that biological processes could be understood in terms of physics and chemistry, and that their growth resembled that of inorganic crystals immersed in solutions of sodium silicate. His ideas, set out in his book La biologie synthétique , were widely dismissed during his lifetime, but has incurred
5040-610: Is a quality that distinguishes matter that has biological processes , such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis , organisation , metabolism , growth , adaptation , response to stimuli , and reproduction . All life over time eventually reaches a state of death , and none is immortal . Many philosophical definitions of living systems have been proposed, such as self-organizing systems. Viruses in particular make definition difficult as they replicate only in host cells. Life exists all over
5184-556: Is about 4.54 billion years . Life on Earth has existed for at least 3.5 billion years, with the oldest physical traces of life dating back 3.7 billion years. Estimates from molecular clocks, as summarised in the TimeTree public database, place the origin of life around 4.0 billion years ago. Hypotheses on the origin of life attempt to explain the formation of a universal common ancestor from simple organic molecules via pre-cellular life to protocells and metabolism. In 2016,
5328-496: Is also important for the lumber industry , as logs can be shipped via river. Countries with dense forests and networks of rivers like Sweden have historically benefited the most from this method of trade. The rise of highways and the automobile has made this practice less common. One of the first large canals was the Canal du Midi , connecting rivers within France to create a path from
5472-552: Is an ancient dam built on the Nile 4,500 years ago. The Ancient Roman civilization used aqueducts to transport water to urban areas . Spanish Muslims used mills and water wheels beginning in the seventh century. Between 130 and 1492, larger dams were built in Japan, Afghanistan, and India, including 20 dams higher than 15 metres (49 ft). Canals began to be cut in Egypt as early as 3000 BC, and
5616-448: Is at a higher elevation than the river itself, and in these areas, water flows downhill into the river. The headwaters of a river are the smaller streams that feed a river, and make up the river's source. These streams may be small and flow rapidly down the sides of mountains . All of the land uphill of a river that feeds it with water in this way is in that river's drainage basin or watershed. A ridge of higher elevation land
5760-405: Is because any natural impediment to the flow of the river may cause the current to deflect in a different direction. When this happens, the alluvium carried by the river can build up against this impediment, redirecting the course of the river. The flow is then directed against the opposite bank of the river, which will erode into a more concave shape to accommodate the flow. The bank will still block
5904-558: Is capable of forming the various specialised cells that form the adult organism. This specialisation allows multicellular organisms to exploit resources more efficiently than single cells. About 800 million years ago, a minor genetic change in a single molecule, the enzyme GK-PID , may have allowed organisms to go from a single cell organism to one of many cells. Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability. Cell signalling coordinates cellular activities, and hence governs
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6048-422: Is considered the starting point of modern organic chemistry . It is of historical significance because for the first time an organic compound was produced in inorganic reactions. During the 1850s Hermann von Helmholtz , anticipated by Julius Robert von Mayer , demonstrated that no energy is lost in muscle movement, suggesting that there were no "vital forces" necessary to move a muscle. These results led to
6192-453: Is correlated with and thus can be used to predict certain data points related to rivers, such as the size of the drainage basin (drainage area), and the length of the channel. The ecosystem of a river includes the life that lives in its water, on its banks, and in the surrounding land. The width of the channel of a river, its velocity, and how shaded it is by nearby trees. Creatures in a river ecosystem may be divided into many roles based on
6336-580: Is delegated to the individual states that are authorized by the Environmental Protection Agency (EPA). Facilities that apply for a permit must specify the number of outfalls at the site. According to the EPA's Multi-Sector General Permit For Stormwater Discharges Associated With Industrial Activity , outfalls are locations where the stormwater exits the facility, including pipes, ditches, swales, and other structures that transport stormwater. If there
6480-421: Is extended by the evolution of novel functions over time. Death is the termination of all vital functions or life processes in an organism or cell. One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins. However, determining when death has occurred is difficult, as cessation of life functions
6624-497: Is in part because of a projected loss of snowpack in mountains, meaning that melting snow can't replenish rivers during warm summer months, leading to lower water levels. Lower-level rivers also have warmer temperatures, threatening species like salmon that prefer colder upstream temperatures. Attempts have been made to regulate the exploitation of rivers to preserve their ecological functions. Many wetland areas have become protected from development. Water restrictions can prevent
6768-425: Is its soul (Greek psyche , Latin anima ). There are three kinds of souls: the vegetative soul of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the animal soul , which causes animals to move and feel; and the rational soul , which is the source of consciousness and reasoning, which (Aristotle believed) is found only in man. Each higher soul has all of
6912-413: Is more than one outfall present, measure at the primary outfall (i.e., the outfall with the largest volume of stormwater discharge associated with industrial activity). Outfalls from sewage plants can be up to 20 feet (6.1 m) in diameter and release 4,000 US gallons per second (55,000 m/h) of treated human waste miles from the shore. A wastewater treatment system discharges treated effluent to
7056-407: Is most likely to exist, within wide bounds of uncertainty. A "Confidence of Life Detection" scale (CoLD) for reporting evidence of life beyond Earth has been proposed. Artificial life is the simulation of any aspect of life, as through computers, robotics , or biochemistry . Synthetic biology is a new area of biotechnology that combines science and biological engineering . The common goal
7200-470: Is not only plausible, but probable or inevitable, possibly resulting in a biophysical cosmology instead of a mere physical cosmology . Other planets and moons in the Solar System and other planetary systems are being examined for evidence of having once supported simple life, and projects such as SETI are trying to detect radio transmissions from possible alien civilisations. Other locations within
7344-428: Is often not simultaneous across organ systems. Such determination, therefore, requires drawing conceptual lines between life and death. This is problematic because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for
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#17330860418097488-580: Is only known to exist on Earth but extraterrestrial life is thought probable . Artificial life is being simulated and explored by scientists and engineers. The definition of life has long been a challenge for scientists and philosophers. This is partially because life is a process, not a substance. This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth. Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from
7632-485: Is organised into chromosomes . All species of large complex organisms are eukaryotes, including animals, plants and fungi, though with a wide diversity of protist microorganisms . The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through endosymbiosis between bacteria and the progenitor eukaryotic cell. The molecular mechanisms of cell biology are based on proteins . Most of these are synthesised by
7776-402: Is part of permafrost ice caps, or trace amounts of water vapor in the atmosphere. However, there is evidence that rivers flowed on Mars for at least 100,000 years. The Hellas Planitia is a crater left behind by an impact from an asteroid. It has sedimentary rock that was formed 3.7 billion years ago, and lava fields that are 3.3 billion years old. High resolution images of the surface of
7920-560: Is rarely static, the exact location of a river border may be called into question by countries. The Rio Grande between the United States and Mexico is regulated by the International Boundary and Water Commission to manage the right to fresh water from the river, as well as mark the exact location of the border. Up to 60% of fresh water used by countries comes from rivers that cross international borders. This can cause disputes between countries that live upstream and downstream of
8064-671: Is that of the Mississippi River , whose drainage basin covers 40% of the contiguous United States . The river was then used for shipping crops from the American Midwest and cotton from the American South to other states as well as the Atlantic Ocean. The role of urban rivers has evolved from when they were a center of trade, food, and transportation to modern times when these uses are less necessary. Rivers remain central to
8208-539: Is the Sunswick Creek in New York City, which was covered in the 1800s and now exists only as a sewer-like pipe. While rivers may flow into lakes or man-made features such as reservoirs , the water they contain will always tend to flow down toward the ocean . However, if human activity siphons too much water away from a river for other uses, the riverbed may run dry before reaching the sea. The outlets mouth of
8352-417: Is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of biotechnology, with the ultimate goals of being able to design and build engineered biological systems that process information, manipulate chemicals, fabricate materials and structures, produce energy, provide food, and maintain and enhance human health and
8496-434: Is to define life as "a self-sustained chemical system capable of undergoing Darwinian evolution ", a definition adopted by a NASA committee attempting to define life for the purposes of exobiology , based on a suggestion by Carl Sagan . This definition, however, has been widely criticised because according to it, a single sexually reproducing individual is not alive as it is incapable of evolving on its own. Others take
8640-509: Is unlikely or impossible. Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance. To survive, some microorganisms have evolved to withstand freezing , complete desiccation , starvation , high levels of radiation exposure , and other physical or chemical challenges. These extremophile microorganisms may survive exposure to such conditions for long periods. They excel at exploiting uncommon sources of energy. Characterization of
8784-808: Is what typically separates drainage basins; water on one side of a ridge will flow into one set of rivers, and water on the other side will flow into another. One example of this is the Continental Divide of the Americas in the Rocky Mountains . Water on the western side of the divide flows into the Pacific Ocean , whereas water on the other side flows into the Atlantic Ocean . Not all precipitation flows directly into rivers; some water seeps into underground aquifers . These, in turn, can still feed rivers via
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#17330860418098928-587: The 2024 Summer Olympics . Another example is the restoration of the Isar in Munich from being a fully canalized channel with hard embankments to being wider with naturally sloped banks and vegetation. This has improved wildlife habitat in the Isar, and provided more opportunities for recreation in the river. As a natural barrier , rivers are often used as a border between countries , cities, and other territories . For example,
9072-479: The Atlantic Ocean to the Mediterranean Sea . The nineteenth century saw canal-building become more common, with the U.S. building 4,400 miles (7,100 km) of canals by 1830. Rivers began to be used by cargo ships at a larger scale, and these canals were used in conjunction with river engineering projects like dredging and straightening to ensure the efficient flow of goods. One of the largest such projects
9216-492: The Industrial Revolution as a source of power for textile mills and other factories, but were eventually supplanted by steam power . Rivers became more industrialized with the growth of technology and the human population . As fish and water could be brought from elsewhere, and goods and people could be transported via railways , pre-industrial river uses diminished in favor of more complex uses. This meant that
9360-692: The International Ocean Discovery Program found unicellular life in 120 °C sediment 1.2 km below seafloor in the Nankai Trough subduction zone. According to one researcher, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or chemical energy ), water, heat, atmosphere , gravity , nutrients , and ultraviolet solar radiation protection . In most ecosystems,
9504-755: The Lamari River in New Guinea separates the Angu and the Fore people in New Guinea. The two cultures speak different languages and rarely mix. 23% of international borders are large rivers (defined as those over 30 meters wide). The traditional northern border of the Roman Empire was the Danube , a river that today forms the border of Hungary and Slovakia . Since the flow of a river
9648-517: The Nile and the Ganges . The Quran describes these four rivers as flowing with water, milk, wine, and honey, respectively. The book of Genesis also contains a story of a great flood . Similar myths are present in the Epic of Gilgamesh , Sumerian mythology, and in other cultures. In Genesis, the flood's role was to cleanse Earth of the wrongdoing of humanity. The act of water working to cleanse humans in
9792-496: The Nuvvuagittuq Belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on Earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago , and not long after the formation of the Earth 4.54 billion years ago. Evolution is the change in heritable characteristics of biological populations over successive generations. It results in
9936-558: The River Continuum Concept . "Shredders" are organisms that consume this organic material. The role of a "grazer" or "scraper" organism is to feed on the algae that collects on rocks and plants. "Collectors" consume the detritus of dead organisms. Lastly, predators feed on living things to survive. The river can then be modeled by the availability of resources for each creature's role. A shady area with deciduous trees might experience frequent deposits of organic matter in
10080-608: The River Lethe to forget their previous life. Rivers also appear in descriptions of paradise in Abrahamic religions , beginning with the story of Genesis . A river beginning in the Garden of Eden waters the garden and then splits into four rivers that flow to provide water to the world. These rivers include the Tigris and Euphrates , and two rivers that are possibly apocryphal but may refer to
10224-458: The Solar System that may host microbial life include the subsurface of Mars , the upper atmosphere of Venus , and subsurface oceans on some of the moons of the giant planets . Investigation of the tenacity and versatility of life on Earth, as well as an understanding of the molecular systems that some organisms utilise to survive such extremes, is important for the search for extraterrestrial life. For example, lichen could survive for
10368-753: The Sumerians in the Tigris–Euphrates river system , the Ancient Egyptian civilization in the Nile, and the Indus Valley Civilization on the Indus River . The desert climates of the surrounding areas made these societies especially reliant on rivers for survival, leading to people clustering in these areas to form the first cities . It is also thought that these civilizations were the first to organize
10512-485: The climate . The alluvium carried by rivers, laden with minerals, is deposited into the floodplain when the banks spill over, providing new nutrients to the soil, allowing them to support human activity like farming as well as a host of plant and animal life. Deposited sediment from rivers can form temporary or long-lasting fluvial islands . These islands exist in almost every river. About half of all waterways on Earth are intermittent rivers , which do not always have
10656-665: The cultural identity of cities and nations. Famous examples include the River Thames 's relationship to London , the Seine to Paris , and the Hudson River to New York City . The restoration of water quality and recreation to urban rivers has been a goal of modern administrations. For example, swimming was banned in the Seine for over 100 years due to concerns about pollution and the spread of E. coli , until cleanup efforts to allow its use in
10800-478: The discharge of a river, the amount of water passing through it at a particular time. The flow of a river can act as a means of transportation for plant and animal species, as well as a barrier. For example, the Amazon River is so wide in parts that the variety of species on either side of its basin are distinct. Some fish may swim upstream to spawn as part of a seasonal migration . Species that travel from
10944-465: The extinction of some species, and lowered the amount of alluvium flowing through rivers. Decreased snowfall from climate change has resulted in less water available for rivers during the summer. Regulation of pollution, dam removal , and sewage treatment have helped to improve water quality and restore river habitats. A river is a natural flow of freshwater that flows on or through land towards another body of water downhill. This flow can be into
11088-436: The sea . The sediment yield of a river is the quantity of sand per unit area within a watershed that is removed over a period of time. The monitoring of the sediment yield of a river is important for ecologists to understand the health of its ecosystems, the rate of erosion of the river's environment, and the effects of human activity. Rivers rarely run in a straight direction, instead preferring to bend or meander . This
11232-480: The soul , or resurrection of the body at a later date. Whether or not viruses should be considered as alive is controversial. They are most often considered as just gene coding replicators rather than forms of life. They have been described as "organisms at the edge of life" because they possess genes , evolve by natural selection, and replicate by making multiple copies of themselves through self-assembly. However, viruses do not metabolise and they require
11376-467: The structure and metabolic diversity of microbial communities in such extreme environments is ongoing. The first classification of organisms was made by the Greek philosopher Aristotle (384–322 BC), who grouped living things as either plants or animals, based mainly on their ability to move. He distinguished animals with blood from animals without blood, which can be compared with the concepts of vertebrates and invertebrates respectively, and divided
11520-521: The water table , the groundwater beneath the surface of the land stored in the soil . Water flows into rivers in places where the river's elevation is lower than that of the water table. This phenomenon is why rivers can still flow even during times of drought . Rivers are also fed by the melting of snow glaciers present in higher elevation regions. In summer months, higher temperatures melt snow and ice, causing additional water to flow into rivers. Glacier melt can supplement snow melt in times like
11664-488: The Earth in air, water, and soil , with many ecosystems forming the biosphere . Some of these are harsh environments occupied only by extremophiles . Life has been studied since ancient times, with theories such as Empedocles 's materialism asserting that it was composed of four eternal elements , and Aristotle 's hylomorphism asserting that living things have souls and embody both form and matter. Life originated at least 3.5 billion years ago, resulting in
11808-454: The Sun-like "main sequence" of stellar evolution for a shorter time interval. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits. Hence, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop. The location of
11952-403: The abandonment of scientific interest in vitalistic theories, especially after Eduard Buchner 's demonstration that alcoholic fermentation could occur in cell-free extracts of yeast. Nonetheless, belief still exists in pseudoscientific theories such as homoeopathy , which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force. The age of Earth
12096-466: The appearance of new species and often the disappearance of old ones. Evolution occurs when evolutionary processes such as natural selection (including sexual selection ) and genetic drift act on genetic variation, resulting in certain characteristics increasing or decreasing in frequency within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation . Fossils are
12240-450: The attributes of the lower ones. Aristotle believed that while matter can exist without form, form cannot exist without matter, and that therefore the soul cannot exist without the body. This account is consistent with teleological explanations of life , which account for phenomena in terms of purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality (from
12384-399: The basic functions of multicellular organisms. Signaling between cells can occur through direct cell contact using juxtacrine signalling , or indirectly through the exchange of agents as in the endocrine system . In more complex organisms, coordination of activities can occur through a dedicated nervous system . Though life is confirmed only on Earth, many think that extraterrestrial life
12528-436: The biosphere, including soil , hot springs , inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere. For example, spores of Aspergillus niger have been detected in the mesosphere at an altitude of 48 to 77 km. Under test conditions, life forms have been observed to survive in the vacuum of space. Life forms thrive in
12672-457: The blooded animals into five groups: viviparous quadrupeds ( mammals ), oviparous quadrupeds (reptiles and amphibians ), birds, fishes and whales . The bloodless animals were divided into five groups: cephalopods , crustaceans , insects (which included the spiders, scorpions , and centipedes ), shelled animals (such as most molluscs and echinoderms ), and " zoophytes " (animals that resemble plants). This theory remained dominant for more than
12816-695: The bodies of humans and animals worldwide, as well as in the soil, with potentially negative health effects. Research into how to remove it from the environment, and how harmful exposure is, is ongoing. Fertilizer from farms can lead to a proliferation of algae on the surface of rivers and oceans, which prevents oxygen and light from dissolving into water, making it impossible for underwater life to survive in these so-called dead zones . Urban rivers are typically surrounded by impermeable surfaces like stone, asphalt , and concrete. Cities often have storm drains that direct this water to rivers. This can cause flooding risk as large amounts of water are directed into
12960-405: The complete draining of rivers. Limits on the construction of dams, as well as dam removal , can restore the natural habitats of river species. Regulators can also ensure regular releases of water from dams to keep animal habitats supplied with water. Limits on pollutants like pesticides can help improve water quality. Today, the surface of Mars does not have liquid water. All water on Mars
13104-412: The conditions vary during the day and from one season to the next. To live in most ecosystems, then, organisms must be able to survive a range of conditions, called the "range of tolerance". Outside that are the "zones of physiological stress", where the survival and reproduction are possible but not optimal. Beyond these zones are the "zones of intolerance", where survival and reproduction of that organism
13248-422: The deep Mariana Trench , and inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of the northwestern United States, and 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. In 2014, life forms were found living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. Expeditions of
13392-436: The effect of normalizing the effects of rivers; the greatest floods are smaller and more predictable, and larger sections are open for navigation by boats and other watercraft. A major effect of river engineering has been a reduced sediment output of large rivers. For example, the Mississippi River produced 400 million tons of sediment per year. Due to the construction of reservoirs , sediment buildup in man-made levees , and
13536-523: The exception being sulfur. The latter is a component of the amino acids cysteine and methionine . The most abundant of these elements in organisms is carbon, which has the desirable attribute of forming multiple, stable covalent bonds . This allows carbon-based (organic) molecules to form the immense variety of chemical arrangements described in organic chemistry . Alternative hypothetical types of biochemistry have been proposed that eliminate one or more of these elements, swap out an element for one not on
13680-451: The fish zonation concept. Smaller rivers can only sustain smaller fish that can comfortably fit in its waters, whereas larger rivers can contain both small fish and large fish. This means that larger rivers can host a larger variety of species. This is analogous to the species-area relationship , the concept of larger habitats being host to more species. In this case, it is known as the species-discharge relationship, referring specifically to
13824-665: The floating of wood on rivers to transport it, was especially important. Rivers also were an important source of drinking water . For civilizations built around rivers, fish were an important part of the diet of humans. Some rivers supported fishing activities, but were ill-suited to farming, such as those in the Pacific Northwest . Other animals that live in or near rivers like frogs , mussels , and beavers could provide food and valuable goods such as fur . Humans have been building infrastructure to use rivers for thousands of years. The Sadd el-Kafara dam near Cairo , Egypt,
13968-412: The flow of the river beneath its surface. These help rivers flow straighter by increasing the speed of the water at the middle of the channel, helping to control floods. Levees are also used for this purpose. They can be thought of as dams constructed on the sides of rivers, meant to hold back water from flooding the surrounding area during periods of high rainfall. They are often constructed by building up
14112-399: The flow, causing it to reflect in the other direction. Thus, a bend in the river is created. Rivers may run through low, flat regions on their way to the sea. These places may have floodplains that are periodically flooded when there is a high level of water running through the river. These events may be referred to as "wet seasons' and "dry seasons" when the flooding is predictable due to
14256-650: The form of leaves. In this type of ecosystem, collectors and shredders will be most active. As the river becomes deeper and wider, it may move slower and receive more sunlight . This supports invertebrates and a variety of fish , as well as scrapers feeding on algae. Further downstream, the river may get most of its energy from organic matter that was already processed upstream by collectors and shredders. Predators may be more active here, including fish that feed on plants, plankton , and other fish. The flood pulse concept focuses on habitats that flood seasonally, including lakes and marshes . The land that interfaces with
14400-409: The formation of colonies of identical cells. These cells can form group organisms through cell adhesion . The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specialisations, making them dependent on the remainder of the organism for survival. Such organisms are formed clonally or from a single germ cell that
14544-470: The formation of Earth's major animal and plant species. This interplay between organisms and their environment is an inherent feature of living systems. The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. Organisms exist in every part of
14688-406: The fungi are more closely related to animals than to plants. As advances in microscopy enabled detailed study of cells and microorganisms, new groups of life were revealed, and the fields of cell biology and microbiology were created. These new organisms were originally described separately in protozoa as animals and protophyta/thallophyta as plants, but were united by Ernst Haeckel in
14832-480: The future to the past) is in contradiction with the scientific evidence for natural selection, which explains the consequence in terms of a prior cause. Biological features are explained not by looking at future optimal results, but by looking at the past evolutionary history of a species, which led to the natural selection of the features in question. Spontaneous generation was the belief that living organisms can form without descent from similar organisms. Typically,
14976-426: The given environment. This implies all or most of the following traits: From a physics perspective, an organism is a thermodynamic system with an organised molecular structure that can reproduce itself and evolve as survival dictates. Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. Another way of putting this
15120-502: The goddess Isis were said to be the cause of the river's yearly flooding, itself personified by the goddess Hapi . Many African religions regard certain rivers as the originator of life. In Yoruba religion , Yemọja rules over the Ogun River in modern-day Nigeria and is responsible for creating all children and fish. Some sacred rivers have religious prohibitions attached to them, such as not being allowed to drink from them or ride in
15264-434: The idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from mud or garbage. The theory of spontaneous generation was proposed by Aristotle , who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it was considered the best explanation for two millennia. It
15408-496: The information to be preserved during reproduction and cell division. Within cells, DNA is organised into long structures called chromosomes . During cell division these chromosomes are duplicated in the process of DNA replication , providing each cell its own complete set of chromosomes. Eukaryotes store most of their DNA inside the cell nucleus . Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by division . Cell theory
15552-428: The irrigation of desert environments for growing food. Growing food at scale allowed people to specialize in other roles, form hierarchies, and organize themselves in new ways, leading to the birth of civilization. In pre-industrial society , rivers were a source of transportation and abundant resources. Many civilizations depended on what resources were local to them to survive. Shipping of commodities, especially
15696-632: The kingdom Protista ; later, the prokaryotes were split off in the kingdom Monera , which would eventually be divided into two separate groups, the Bacteria and the Archaea . This led to the six-kingdom system and eventually to the current three-domain system , which is based on evolutionary relationships. However, the classification of eukaryotes, especially of protists, is still controversial. As microbiology developed, viruses, which are non-cellular, were discovered. Whether these are considered alive has been
15840-440: The landscape around it, forming deltas and islands where the flow slows down. Rivers rarely run in a straight line, instead, they bend or meander ; the locations of a river's banks can change frequently. Rivers get their alluvium from erosion , which carves rock into canyons and valleys . Rivers have sustained human and animal life for millennia, including the first human civilizations . The organisms that live around or in
15984-434: The late summer, when there may be less snow left to melt, helping to ensure that the rivers downstream of the glaciers have a continuous supply of water. Rivers flow downhill, with their direction determined by gravity . A common misconception holds that all or most rivers flow from North to South, but this is not true. As rivers flow downstream, they eventually merge to form larger rivers. A river that feeds into another
16128-469: The level of river branching in a drainage basin. Several systems of stream order exist, one of which is the Strahler number . In this system, the first tributaries of a river are 1st order rivers. When two 1st order rivers merge, the resulting river is 2nd order. If a river of a higher order and a lower order merge, the order is incremented from whichever of the previous rivers had the higher order. Stream order
16272-563: The list, or change required chiralities or other chemical properties. Deoxyribonucleic acid or DNA is a molecule that carries most of the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids ; alongside proteins and complex carbohydrates , they are one of the three major types of macromolecule that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form
16416-561: The local ecosystems of rivers needed less protection as humans became less reliant on them for their continued flourishing. River engineering began to develop projects that enabled industrial hydropower , canals for the more efficient movement of goods, as well as projects for flood prevention . River transportation has historically been significantly cheaper and faster than transportation by land. Rivers helped fuel urbanization as goods such as grain and fuel could be floated downriver to supply cities with resources. River transportation
16560-407: The mechanical shadoof began to be used to raise the elevation of water. Drought years harmed crop yields, and leaders of society were incentivized to ensure regular water and food availability to remain in power. Engineering projects like the shadoof and canals could help prevent these crises. Despite this, there is evidence that floodplain-based civilizations may have been abandoned occasionally at
16704-508: The middle of the 19th century. It appealed to philosophers such as Henri Bergson , Friedrich Nietzsche , and Wilhelm Dilthey , anatomists like Xavier Bichat , and chemists like Justus von Liebig . Vitalism included the idea that there was a fundamental difference between organic and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828, when Friedrich Wöhler prepared urea from inorganic materials. This Wöhler synthesis
16848-400: The migration routes of fish and destroy habitats. Rivers that flow freely from headwaters to the sea have better water quality, and also retain their ability to transport nutrient-rich alluvium and other organic material downstream, keeping the ecosystem healthy. The creation of a lake changes the habitat of that portion of water, and blocks the transportation of sediment, as well as preventing
16992-399: The natural meandering of the river. Dams block the migration of fish such as salmon for which fish ladder and other bypass systems have been attempted, but these are not always effective. Pollution from factories and urban areas can also damage water quality. " Per- and polyfluoroalkyl substances (PFAS) is a widely used chemical that breaks down at a slow rate. It has been found in
17136-429: The natural terrain with soil or clay. Some levees are supplemented with floodways, channels used to redirect floodwater away from farms and populated areas. Dams restrict the flow of water through a river. They can be built for navigational purposes, providing a higher level of water upstream for boats to travel in. They may also be used for hydroelectricity , or power generation from rivers. Dams typically transform
17280-448: The non-living. Legal definitions of life have been debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision. At least 123 definitions of life have been compiled. Since there is no consensus for a definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in
17424-560: The oldest from the Archaean Eon, up to 3.4 billion years old. Extinction is the process by which a species dies out. The moment of extinction is the death of the last individual of that species. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in changing habitat or against superior competition. Over 99% of all
17568-606: The parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of fission in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In eukaryotes , a more complex process of mitosis is followed. However, the result is the same; the resulting cell copies are identical to each other and to the original cell (except for mutations ), and both are capable of further division following an interphase period. Multicellular organisms may have first evolved through
17712-425: The plain show evidence of a river network, and even river deltas. These images reveal channels formed in the rock, recognized by geologists who study rivers on Earth as being formed by rivers, as well as "bench and slope" landforms, outcroppings of rock that show evidence of river erosion. Not only do these formations suggest that rivers once existed, but that they flowed for extensive time periods, and were part of
17856-466: The preserved remains or traces of organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in layers ( strata ) of sedimentary rock is known as the fossil record . A preserved specimen is called a fossil if it is older than the arbitrary date of 10,000 years ago. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to
18000-448: The removal of natural banks replaced with revetments , this sediment output has been reduced by 60%. The most basic river projects involve the clearing of obstructions like fallen trees. This can scale up to dredging , the excavation of sediment buildup in a channel, to provide a deeper area for navigation. These activities require regular maintenance as the location of the river banks changes over time, floods bring foreign objects into
18144-530: The reverse, death and destruction, especially through floods . This power has caused rivers to have a central role in religion , ritual , and mythology . In Greek mythology , the underworld is bordered by several rivers. Ancient Greeks believed that the souls of those who perished had to be borne across the River Styx on a boat by Charon in exchange for money. Souls that were judged to be good were admitted to Elysium and permitted to drink water from
18288-456: The ribosomes through an enzyme-catalyzed process called protein biosynthesis . A sequence of amino acids is assembled and joined based upon gene expression of the cell's nucleic acid. In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination. Cells reproduce through a process of cell division in which
18432-461: The river, and natural sediment buildup continues. Artificial channels are often constructed to "cut off" winding sections of a river with a shorter path, or to direct the flow of a river in a straighter direction. This effect, known as channelization, has made the distance required to traverse the Missouri River in 116 kilometres (72 mi) shorter. Dikes are channels built perpendicular to
18576-552: The river. Areas of a river with softer rock weather faster than areas with harder rock, causing a difference in elevation between two points of a river. This can cause the formation of a waterfall as the river's flow falls down a vertical drop. A river in a permeable area does not exhibit this behavior and may even have raised banks due to sediment. Rivers also change their landscape through their transportation of sediment , often known as alluvium when applied specifically to rivers. This debris comes from erosion performed by
18720-620: The river. A country that is downstream of another may object to the upstream country diverting too much water for agricultural uses, pollution, as well as the creation of dams that change the river's flow characteristics. For example, Egypt has an agreement with Sudan requiring a specific minimum volume of water to pass into the Nile yearly over the Aswan Dam , to maintain both countries access to water. The importance of rivers throughout human history has given them an association with life and fertility . They have also become associated with
18864-457: The rivers themselves, debris swept into rivers by rainfall, as well as erosion caused by the slow movement of glaciers. The sand in deserts and the sediment that forms bar islands is from rivers. The particle size of the debris is gradually sorted by the river, with heavier particles like rocks sinking to the bottom, and finer particles like sand or silt carried further downriver . This sediment may be deposited in river valleys or carried to
19008-412: The rivers. Due to these impermeable surfaces, these rivers often have very little alluvium carried in them, causing more erosion once the river exits the impermeable area. It has historically been common for sewage to be directed directly to rivers via sewer systems without being treated, along with pollution from industry. This has resulted in a loss of animal and plant life in urban rivers, as well as
19152-409: The sea from their mouths. Depending on the activity of waves, the strength of the river, and the strength of the tidal current, the sediment can accumulate to form new land. When viewed from above, a delta can appear to take the form of several triangular shapes as the river mouth appears to fan out from the original coastline . In hydrology , a stream order is a positive integer used to describe
19296-414: The sea to breed in freshwater rivers are anadromous. Salmon are an anadromous fish that may die in the river after spawning, contributing nutrients back to the river ecosystem. Modern river engineering involves a large-scale collection of independent river engineering structures that have the goal of flood control , improved navigation, recreation, and ecosystem management. Many of these projects have
19440-435: The soul, like everything else, was composed of fiery atoms. He elaborated on fire because of the apparent connection between life and heat, and because fire moves. Plato , in contrast, held that the world was organised by permanent forms , reflected imperfectly in matter; forms provided direction or intelligence, explaining the regularities observed in the world. The mechanistic materialism that originated in ancient Greece
19584-493: The species that have ever lived are now extinct. Mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. The diversity of life on Earth is a result of the dynamic interplay between genetic opportunity , metabolic capability, environmental challenges, and symbiosis . For most of its existence, Earth's habitable environment has been dominated by microorganisms and subjected to their metabolism and evolution. As
19728-519: The spread of waterborne diseases such as cholera . In modern times, sewage treatment and controls on pollution from factories have improved the water quality of urban rivers. Climate change can change the flooding cycles and water supply available to rivers. Floods can be larger and more destructive than expected, causing damage to the surrounding areas. Floods can also wash unhealthy chemicals and sediment into rivers. Droughts can be deeper and longer, causing rivers to run dangerously low. This
19872-484: The star within a galaxy may also affect the likelihood of life forming. Stars in regions with a greater abundance of heavier elements that can form planets, in combination with a low rate of potentially habitat -damaging supernova events, are predicted to have a higher probability of hosting planets with complex life. The variables of the Drake equation are used to discuss the conditions in planetary systems where civilisation
20016-408: The sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone . According to base pairing rules (A with T, and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. This has the key property that each strand contains all the information needed to recreate the other strand, enabling
20160-410: The surface of the Earth. Rivers flow in channeled watercourses and merge in confluences to form drainage basins , areas where surface water eventually flows to a common outlet. Rivers have a great effect on the landscape around them. They may regularly overflow their banks and flood the surrounding area, spreading nutrients to the surrounding area. Sediment or alluvium carried by rivers shapes
20304-413: The universe is made up of a combination of four eternal "elements" or "roots of all": earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. Democritus (460 BC) was an atomist ; he thought that the essential characteristic of life was having a soul ( psyche ), and that
20448-414: Was decisively dispelled by the experiments of Louis Pasteur in 1859, who expanded upon the investigations of predecessors such as Francesco Redi . Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists. Vitalism is the belief that there is a non-material life-principle. This originated with Georg Ernst Stahl (17th century), and remained popular until
20592-495: Was formulated by Henri Dutrochet , Theodor Schwann , Rudolf Virchow and others during the early nineteenth century, and subsequently became widely accepted. The activity of an organism depends on the total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information that is carried forward as a genetic code during cell division. There are two primary types of cells, reflecting their evolutionary origins. Prokaryote cells lack
20736-482: Was revived and revised by the French philosopher René Descartes (1596–1650), who held that animals and humans were assemblages of parts that together functioned as a machine. This idea was developed further by Julien Offray de La Mettrie (1709–1750) in his book L'Homme Machine . In the 19th century the advances in cell theory in biological science encouraged this view. The evolutionary theory of Charles Darwin (1859)
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