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The Day The Earth Nearly Died Genre Country of origin United Kingdom Original language(s) English Production Running time 49 minutes Release Original network Original release 5 December 2002 The Day The Earth Nearly Died is a British documentary produced by to the and series in 2002. The program focuses on the mystery of the, which scientists believe killed over 90% of all life on earth at the end of the, some 250 million years ago. The program features scientists like, and others. Synopsis. References.

When Life Nearly Died Book
When Life Nearly Died
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. Life is a characteristic that distinguishes that do have, such as and processes, from those that do not, either because such functions have, or because they never had such functions and are classified as.

Various forms of life exist, such as plants, animals, and bacteria. The criteria can at times be ambiguous and may or may not define viruses, or potential as 'living'. Is the primary science concerned with the study of life, although many other sciences are involved. The definition of life is controversial.

The current definition is that maintain, are composed of, undergo, can, to their environment, respond to, and. However, many other biological definitions have been proposed, and there are some borderline cases of life, such as viruses. Throughout history, there have been many attempts to define what is meant by 'life' and many theories on the properties and emergence of living things, such as, the belief that everything is made out of matter and that life is merely a complex form of it;, the belief that all things are a combination of matter and form, and the form of a living thing is its soul;, the belief that life repeatedly emerges from non-life; and, a now largely discredited hypothesis that living organisms possess a 'life force' or 'vital spark'. Modern definitions are more complex, with input from a diversity of scientific disciplines. Have proposed many definitions based on chemical; there are also some, such as the, the idea that the itself is alive. Another theory is that life is the property of, and yet another is elaborated in, a branch or subfield of. Describes the natural process of life arising from non-living matter, such as simple.

Properties common to all organisms include the need for certain core to sustain functions. Life on Earth as early as 4.28 billion years ago, soon after, and not long after the 4.54 billion years ago. Earth's current life may have descended from an, although -based life may not have been the first. The mechanism by which is unknown, though many hypotheses have been formulated and are often based on the.

The are microfossils of bacteria. In July 2016, scientists reported identifying a set of 355 thought to be present in the (LUCA) of all living organisms. Since its primordial beginnings, life on Earth has changed its environment on a. To survive in most, life must often adapt to a wide range of conditions.

Some, called, thrive in physically or geochemically that are detrimental to most other life on Earth. Was the first person to organisms. Later, introduced of for the classification of. Eventually new groups and categories of life were discovered, such as and, forcing dramatic revisions of the structure of relationships between living organisms. Cells are sometimes considered the smallest units and 'building blocks' of life.

There are two kinds of cells, and, both of which consist of enclosed within a and contain many such as and. Cells reproduce through a process of, in which the parent cell divides into two or more daughter cells. Though currently only known on, life need not be restricted to it, and many scientists speculate in the existence of. Is a computer simulation or man-made reconstruction of any aspect of life, which is often used to examine systems related to natural life. Death is the permanent termination of all which sustain an organism, and as such, is the end of its life. Is the process by which an entire group or, normally a, dies out. Are the preserved remains or of organisms.

The characteristics of life Since there is no unequivocal 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 the given environment. This characteristic exhibits all or most of the following traits:.: regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.: being structurally composed of one or more – the basic units of life.: transformation of energy by converting chemicals and energy into cellular components and decomposing organic matter. Living things require to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.: maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size in all of its parts, rather than simply accumulating matter.: the ability to change over time in response to the environment.

This ability is fundamental to the process of and is determined by the organism's, diet, and external factors. Response to: a response can take many forms, from the contraction of a to external chemicals, to complex reactions involving all the senses of. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun , and.: the ability to produce new individual organisms, either from a single parent organism or from two parent organisms. These complex processes, called, have underlying physical and chemical bases, as well as that are essential to maintaining life. Alternative definitions. See also: From a perspective, living beings are with an organized 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.

Hence, life is a self-sustained chemical system capable of undergoing. A major strength of this definition is that it distinguishes life by the evolutionary process rather than its chemical composition. Others take a viewpoint that does not necessarily depend on molecular chemistry.

One systemic definition of life is that living things are and (self-producing). Variations of this definition include 's definition as an or a capable of reproducing itself or themselves, and of completing at least one. This definition is extended by the apparition of novel functions over time. As seen under an electron microscope Whether or not viruses should be considered as alive is controversial.

They are most often considered as just rather than forms of life. They have been described as 'organisms at the edge of life' because they possess, evolve by natural selection, and replicate by creating multiple copies of themselves through self-assembly.

However, viruses do not metabolize and they require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the, as it may support the hypothesis that life could have started as self-assembling. Biophysics To reflect the minimum phenomena required, other biological definitions of life have been proposed, with many of these being based upon chemical. Have commented that living things function on. In other words, living processes can be viewed as a delay of the spontaneous or of the internal energy of biological towards more potential.

In more detail, according to physicists such as, and, life is a member of the class of phenomena that are or continuous systems able to decrease their internal at the expense of substances or taken in from the environment and subsequently rejected in a degraded form. Living systems theories Living systems are open living things that interact with their. These systems are maintained by flows of information, and matter. Some scientists have proposed in the last few decades that a general living systems theory is required to explain the nature of life. Such a general theory would arise out of the ecological and and attempt to map general principles for how all living systems work.

Instead of examining phenomena by attempting to break things down into components, a general living systems theory explores phenomena in terms of dynamic patterns of the relationships of organisms with their environment. Gaia hypothesis. Main article: The idea that the Earth is alive is found in philosophy and religion, but the first scientific discussion of it was by the Scottish scientist. In 1785, he stated that the Earth was a superorganism and that its proper study should be. Hutton is considered the father of geology, but his idea of a living Earth was forgotten in the intense of the 19th century.: 10 The Gaia hypothesis, proposed in the 1960s by scientist, suggests that life on Earth functions as a single organism that defines and maintains conditions necessary for its survival.

This hypothesis served as one of the foundations of the modern. Nonfractionability The first attempt at a general theory for explaining the nature of life was in 1978, by American biologist. (1991) built on this by defining a system component as 'a unit of organization; a part with a function, i.e., a definite relation between part and whole.' From this and other starting concepts, he developed a 'relational theory of systems' that attempts to explain the special properties of life. Specifically, he identified the 'nonfractionability of components in an organism' as the fundamental difference between living systems and 'biological machines.' Life as a property of ecosystems A systems view of life treats environmental and biological fluxes together as a 'reciprocity of influence,' and a reciprocal relation with environment is arguably as important for understanding life as it is for understanding ecosystems.

As (1992) explains it, life is a property of an rather than a single organism or species. He argues that an ecosystemic definition of life is preferable to a strictly or physical one.

(2009) highlights mutualism as the key to understand the systemic, order-generating behavior of life and ecosystems. Complex systems biology.

See also: Complex systems biology (CSB) is a field of science that studies the emergence of complexity in functional organisms from the viewpoint of theory. The latter is also often called and aims to understand the most fundamental aspects of life. A closely related approach to CSB and systems biology called relational biology is concerned mainly with understanding life processes in terms of the most important relations, and categories of such relations among the essential functional components of organisms; for multicellular organisms, this has been defined as 'categorical biology', or a model representation of organisms as a of biological relations, as well as an of the of living organisms in terms of their dynamic, complex of metabolic, genetic, and processes and. Alternative but closely related approaches focus on the interdependance of constraints, where constraints can be either molecular, such as enzymes, or macroscopic, such as the geometry of a bone or of the vascular system.

Darwinian dynamic It has also been argued that the evolution of order in living systems and certain physical systems obeys a common fundamental principle termed the Darwinian dynamic. The Darwinian dynamic was formulated by first considering how macroscopic order is generated in a simple non-biological system far from thermodynamic equilibrium, and then extending consideration to short, replicating molecules. The underlying order-generating process was concluded to be basically similar for both types of systems.

Operator theory Another systemic definition called the operator theory proposes that 'life is a general term for the presence of the typical closures found in organisms; the typical closures are a membrane and an autocatalytic set in the cell' and that an organism is any system with an organisation that complies with an operator type that is at least as complex as the cell. Life can also be modeled as a network of inferior of regulatory mechanisms subordinated to a superior formed by the potential of expansion and reproduction.

History of study Materialism. An aerial photo of microbial mats around the of 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.

(430 BC) argued that everything in the universe is made up of a combination of 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. (460 BC) thought that the essential characteristic of life is having a ( psyche). Like other ancient writers, he was attempting to explain what makes something a living thing. His explanation was that fiery atoms make a soul in exactly the same way atoms and void account for any other thing. He elaborates on fire because of the apparent connection between life and heat, and because fire moves.

Plato's world of eternal and unchanging, imperfectly represented in matter by a divine, contrasts sharply with the various mechanistic, of which was, by the fourth century at least, the most prominent. This debate persisted throughout the ancient world. Atomistic mechanism got a shot in the arm from.

While the adopted a divine teleology. The choice seems simple: either show how a structured, regular world could arise out of undirected processes, or inject intelligence into the system.

The of plants, animals, and humans, according to Hylomorphism is a theory first expressed by the Greek philosopher (322 BC). The application of hylomorphism to biology was important to Aristotle, and. In this view, everything in the material universe has both matter and form, and the form of a living thing is its (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 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 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 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 of a species, which led to the natural selection of the features in question. Spontaneous generation.

Main article: Spontaneous generation was the belief on the ordinary formation of living organisms without descent from similar organisms. Typically, 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, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. It was decisively dispelled by the experiments of in 1859, who expanded upon the investigations of predecessors such as. Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists. Main article: Vitalism is the belief that the life-principle is non-material. This originated with (17th century), and remained popular until the middle of the 19th century.

It appealed to philosophers such as, and, anatomists like, and chemists like. Vitalism included the idea that there was a fundamental difference between organic and inorganic material, and the belief that can only be derived from living things. This was disproved in 1828, when prepared from inorganic materials. This is considered the starting point of modern. It is of historical significance because for the first time an was produced in reactions. During the 1850s, anticipated by, 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 the abandonment of scientific interest in vitalistic theories, although the belief lingered on in theories such as, which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force.

Main article: The is about 4.54 billion years. Evidence suggests that life on Earth has existed for at least 3.5, with the oldest physical of life dating back 3.7 billion years; however, some theories, such as the, suggest that life on Earth may have started even earlier, as early as 4.1–4.4 billion years ago, and the may have begun shortly after the, during an epoch when the was only 10–17 million years old. More than 99% of all species of life forms, amounting to over five billion species, that ever lived on Earth are estimated to be. Although the number of Earth's catalogued species of lifeforms is between 1.2 million and 2 million, the total number of species in the planet is uncertain. Estimates range from 8 million to 100 million, with a more narrow range between 10 and 14 million, but it may be as high as 1 trillion (with only one-thousandth of one percent of the species described) according to studies realized in May 2016. The total amount of related on Earth is estimated at 5.0 x 10 37 and weighs 50 billion tonnes. In comparison, the total mass of the has been estimated to be as much as 4 (trillion tons of ).

In July 2016, scientists reported identifying a set of 355 from the (LUCA) of all organisms living on Earth. All known life forms share fundamental molecular mechanisms, reflecting their; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a, from simple via pre-cellular life to and metabolism.

Models have been divided into 'genes-first' and 'metabolism-first' categories, but a recent trend is the emergence of hybrid models that combine both categories. There is no current as to how life originated. However, most accepted scientific models build on the and the work of, which show that conditions on the primitive Earth favored chemical reactions that synthesize and other organic compounds from inorganic precursors, and spontaneously form, the basic structure of a. Living organisms synthesize, which are of amino acids using instructions encoded by (DNA). Entails intermediary (RNA) polymers. One possibility for how life began is that genes originated first, followed by proteins; the alternative being that proteins came first and then genes. However, because genes and proteins are both required to produce the other, the problem of considering which came first is like that of the.

When Life Nearly Died Book

Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently. Therefore, a possibility, first suggested by, is that the first life was based on, which has the DNA-like properties of information storage and the properties of some proteins. This is called the, and it is supported by the observation that many of the most critical components of cells (those that the slowest) are composed mostly or entirely of RNA. Also, many critical cofactors (, etc.) are either nucleotides or substances clearly related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed, but they were confirmed by in 1986. One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA.

However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor present throughout the reaction. This study makes the RNA world hypothesis more plausible. Geological findings in 2013 showed that reactive species (like ) were in abundance in the ocean before 3.5 Ga, and that easily reacts with aqueous to generate phosphite and. It is hypothesized that -containing from the could have provided early reduced phosphorus, which could react with prebiotic organic molecules to form biomolecules, like. In 2009, experiments demonstrated of a two-component system of RNA enzymes in vitro.

The work was performed in the laboratory of, who stated 'This is the first example, outside of biology, of evolutionary adaptation in a molecular genetic system.' Prebiotic compounds may have originated extraterrestrially. Findings in 2011, based on studies with found on Earth, suggest and RNA components (, and related organic molecules) may be formed in.

In March 2015, NASA scientists reported that, for the first time, complex and of life, including, and, have been formed in the laboratory under conditions, using starting chemicals, such as, found in. Pyrimidine, like (PAHs), the most -rich chemical found in the, may have been formed in or in and gas clouds, according to the scientists. According to the hypothesis, —distributed by, and other —may exist throughout the universe. Environmental conditions. The composition of life forms on Earth by leading to the near-extinction of.

The diversity of life on Earth is a result of the dynamic interplay between, metabolic capability, challenges, and. For most of its existence, Earth's habitable environment has been dominated by and subjected to their metabolism and evolution. As a consequence of these microbial activities, the physical-chemical environment on Earth has been changing on a, thereby affecting the path of evolution of subsequent life. For example, the release of molecular by as a by-product of 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 the formation of Earth's major animal and plant species. This interplay between organisms and their environment is an inherent feature of living systems. Main article: The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. By the most general definition, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the, and. Life forms live in every part of the Earth's, including, 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.

Under certain test conditions, life forms have been observed to thrive in the of space and to. Life forms appear to thrive in the, the deepest spot in the Earth's oceans. Other researchers reported related studies that life forms thrive 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, as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. In August 2014, scientists confirmed the existence of life forms living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. According to one researcher, 'You can find everywhere — they're extremely adaptable to conditions, and survive wherever they are.' The biosphere is postulated to have, beginning with a process of (life created naturally from non-living matter, such as simple organic compounds) or (life created from living matter), at least some 3.5 billion years ago. The earliest evidence for life on Earth includes found in 3.7 billion-year-old from and found in 3.48 billion-year-old from.

More recently, in 2015, 'remains of ' were found in 4.1 billion-year-old rocks in Western Australia. In 2017, putative fossilized (or ) were announced to have been discovered in in the 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, and not long after the 4.54 billion years ago. According to biologist, 'If life arose relatively quickly on Earth. Then it could be common in the.' In a general sense, biospheres are any closed, self-regulating systems containing ecosystems. This includes artificial biospheres such as and, and potentially ones on other planets or moons. Range of tolerance.

Is an that can resist extremes of cold, dehydration, vacuum, acid, and radiation exposure. The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or ), water, temperature, and. In most ecosystems, 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 is unlikely or impossible.

Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance. Further information: To survive, selected microorganisms can assume forms that enable them to withstand, high levels of, and other physical or chemical challenges. These microorganisms may survive exposure to such conditions for weeks, months, years, or even centuries. Are that thrive outside the ranges where life is commonly found. They excel at exploiting uncommon sources of energy. While all organisms are composed of nearly identical, evolution has enabled such microbes to cope with this wide range of physical and chemical conditions. Characterization of the and metabolic diversity of microbial communities in such is ongoing.

Thrive even in the, the deepest spot on the Earth. Microbes also thrive inside up to 1,900 feet (580 m) below the sea floor under 8,500 feet (2,600 m) of ocean. Investigation of the tenacity and versatility of life on Earth, as well as an understanding of the molecular systems that some organisms utilize to survive such extremes, is important for the search for. For example, could survive for a month in a. Chemical elements All life forms require certain core needed for functioning. These include, oxygen, and —the elemental for all organisms —often represented by the acronym. Together these make up, proteins and, the bulk of living matter.

Five of these six elements comprise the chemical components of DNA, the exception being sulfur. The latter is a component of the amino acids and. The most biologically abundant of these elements is carbon, which has the desirable attribute of forming multiple, stable. This allows carbon-based (organic) molecules to form an immense variety of chemical arrangements. Alternative have been proposed that eliminate one or more of these elements, swap out an element for one not on the list, or change required or other chemical properties. Main article: Deoxyribonucleic acid is a that carries most of the instructions used in the growth, development, functioning and of all known living and many viruses.

DNA and are s; alongside and, they are one of the three major types of that are essential for all known forms of life. Most DNA molecules consist of two strands coiled around each other to form a. The two DNA strands are known as since they are composed of called. Each nucleotide is composed of a —either (C), (G), (A), or (T)—as well as a called and a. The nucleotides are joined to one another in a chain by between the sugar of one nucleotide and the phosphate of the next, resulting in an alternating. According to rules (A with T, and C with G), bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA.

The total amount of related DNA on Earth is estimated at 5.0 x 10 37, and weighs 50 billion. In comparison, the total of the has been estimated to be as much as 4 (trillion tons of ).

DNA stores biological information. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. Biological information is replicated as the two strands are separated. A significant portion of DNA (more than 98% for humans) is, meaning that these sections do not serve as patterns for protein sequences. The two strands of DNA run in opposite directions to each other and are therefore.

Attached to each sugar is one of four types of nucleobases (informally, bases). It is the of these four nucleobases along the backbone that encodes biological information. Under the, strands are translated to specify the sequence of within proteins. These RNA strands are initially created using DNA strands as a template in a process called. Within cells, DNA is organized into long structures called.

During these chromosomes are duplicated in the process of, providing each cell its own complete set of chromosomes. (animals, plants, and ) store most of their DNA inside the and some of their DNA in, such as. In contrast, (bacteria and ) store their DNA only in the. Within the chromosomes, proteins such as compact and organize DNA.

These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. DNA was first isolated by in 1869.

Its molecular structure was identified by and in 1953, whose model-building efforts were guided by data acquired. The hierarchy of 's eight major.

Is divided into domains, which are subdivided into further groups. Intermediate minor rankings are not shown. Life is usually classified by eight levels of taxa—domains, kingdoms, phyla, class, order, family, genus, and species.

In May 2016, scientists reported that 1 trillion are estimated to be on Earth currently with only one-thousandth of one percent described. The first known attempt to classify organisms was conducted by the Greek philosopher Aristotle (384–322 BC), who classified all living organisms known at that time as either a plant or an animal, based mainly on their ability to move. He also distinguished animals with blood from animals without blood (or at least without red blood), which can be compared with the concepts of and respectively, and divided the blooded animals into five groups: viviparous quadrupeds , oviparous quadrupeds (reptiles and ), birds, fishes and.

The bloodless animals were also divided into five groups:, insects (which included the spiders, and, in addition to what we define as insects today), shelled animals (such as most and ), and ' (animals that resemble plants). Though Aristotle's work in zoology was not without errors, it was the grandest biological synthesis of the time and remained the ultimate authority for many centuries after his death. The exploration of the Americas revealed large numbers of new plants and animals that needed descriptions and classification. In the latter part of the 16th century and the beginning of the 17th, careful study of animals commenced and was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification. In the late 1740s, introduced his system of 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 a short period Linnaeus had classified them in the taxon in Animalia, but later placed them back in Plantae. Classified the Fungi in his Protoctista, thus partially avoiding the problem but acknowledging their special status. The problem was eventually solved by, when he gave them their own in his.

Shows that the fungi are more closely related to animals than to plants. As new discoveries enabled detailed study of and microorganisms, new groups of life were revealed, and the fields of and were created. These new organisms were originally described separately in as animals and as plants, but were united by in the kingdom; later, the were split off in the kingdom, which would eventually be divided into two separate groups, the Bacteria and the. This led to the and eventually to the current, which is based on evolutionary relationships. However, the classification of eukaryotes, especially of protists, is still controversial. As microbiology, and developed, non-cellular reproducing agents were discovered, such as viruses and. Whether these are considered alive has been 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 can still be classed into 'species' based on their biology and, but many aspects of such a classification remain controversial. In the 1960s a trend called emerged, arranging based on in an. 1735 1866 1925 1938 1969 et al. 1990 1998 2 kingdoms 3 kingdoms (not treated). Main article: Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells.

Was formulated by, 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 occurring within and between them. Cells contain hereditary information that is carried forward as a code during cell division. There are two primary types of cells. Lack a and other membrane-bound, although they have circular DNA and. Bacteria and are two of prokaryotes.

The other primary type of cells are the, which have distinct nuclei bound by a nuclear membrane and membrane-bound organelles, including, rough and smooth, and. In addition, they possess organized chromosomes that store genetic material. All species of large complex organisms are eukaryotes, including animals, plants and fungi, though most species of eukaryote are. The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through between bacteria and the progenitor eukaryotic cell.

The molecular mechanisms of are based on. Most of these are synthesized by the ribosomes through an process called.

A sequence of amino acids is assembled and joined together based upon of the cell's nucleic acid. In eukaryotic cells, these proteins may then be transported and processed through the in preparation for dispatch to their destination. Cells reproduce through a process of in which the parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In, a more complex process of is followed. However, the end result is the same; the resulting cell copies are identical to each other and to the original cell (except for ), and both are capable of further division following an period.

May have first evolved through the formation of like cells. These cells can form group organisms through.

When Life Nearly Died

The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specializations, making them dependent on the remainder of the organism for survival. Such organisms are formed or from a single that is capable of forming the various specialized cells that form the adult organism. This specialization allows multicellular organisms to exploit resources more efficiently than single cells. In January 2016, scientists reported that, a in a single, called GK-PID, may have allowed to go from a to. Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability. Coordinates cellular activities, and hence governs the basic functions of multicellular organisms.

Signaling between cells can occur through direct cell contact using, or indirectly through the exchange of agents as in the. In more complex organisms, coordination of activities can occur through a dedicated. Main articles:, and Though life is confirmed only on Earth, many think that is not only plausible, but probable or inevitable. Other planets and in the and other are being examined for evidence of having once supported simple life, and projects such as are trying to detect radio transmissions from possible alien civilizations. Other locations within the that may host life include the subsurface of, the upper atmosphere of, and subsurface oceans on some of the of the. Beyond the Solar System, the region around another that could support Earth-like life on an Earth-like planet is known as the. 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 the main sequence for a shorter time interval. Small have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of 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 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 -damaging events, are predicted to have a higher probability of hosting planets with complex life. The variables of the are used to discuss the conditions in planetary systems where civilization is most likely to exist. Use of the equation to predict the amount of extraterrestrial life, however, is difficult; because many of the variables are unknown, the equation functions as more of a mirror to what its user already thinks. As a result, the number of civilizations in the galaxy can be estimated as low as 9.1 x 10^-11 or as high as 156 million; for the calculations, see.

Main articles: and Artificial life is the of any aspect of life, as through computers,. The study of artificial life imitates traditional biology by recreating some aspects of biological phenomena.

Scientists study the logic of living systems by creating artificial environments—seeking to understand the complex information processing that defines such systems. While life is, by definition, alive, artificial life is generally referred to as data confined to a environment and existence. Is a new area of that combines science and. The common goal is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of, 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 the environment. Animal corpses, like this, are recycled by the, providing energy and nutrients for living creatures Death is the permanent termination of all vital functions or life processes in an organism or cell. It can occur as a result of an accident, or suicide.

After death, the remains of an organism re-enter the. Organisms may be by a or a and leftover may then be further decomposed by, organisms that recycle, returning it to the environment for reuse in the. 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 is often not simultaneous across organ systems.

Such determination therefore requires drawing conceptual lines between life and death. This is problematic, however, 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 or for the, or of the body at a later date. Main article: Extinction is the process by which a group of or dies out, reducing biodiversity. The moment of extinction is generally considered the death of the last individual of that species.

Because a species' potential 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 or against superior competition. In, over 99% of all the species that have ever lived are extinct; however, may have accelerated evolution by providing opportunities for new groups of organisms to diversify.