[178] 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. [98][99][100] Evidence suggests that life on Earth has existed for at least 3.5 billion years,[101][102][103][104][105][106][107][108][109] with the oldest physical traces of life dating back 3.7 billion years;[110][111][112] however, some theories, such as the Late Heavy Bombardment theory, suggest that life on Earth may have started even earlier, as early as 4.1–4.4 billion years ago,[101][102][103][104][105] and the chemistry leading to life may have begun shortly after the Big Bang, 13.8 billion years ago, during an epoch when the universe was only 10–17 million years old. [71][72] 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 RNA molecules. [113][114][115], More than 99% of all species of life forms, amounting to over five billion species,[116] that ever lived on Earth are estimated to be extinct. A sequence of amino acids is assembled and joined together based upon gene expression of the cell's nucleic acid. Death is the permanent termination of all biological processes which sustain an organism, and as such, is the end of its life. [22][23] Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living. 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. [16] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena that are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form.[54][55]. [184] The problem was eventually solved by Whittaker, when he gave them their own kingdom in his five-kingdom system. ", "Directed panspermia. Extinction is the term describing the dying out of a group or taxon, usually a species. Viruses can still be classed into "species" based on their biology and genetics, but many aspects of such a classification remain controversial. 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. One possibility for how life began is that genes originated first, followed by proteins;[128] the alternative being that proteins came first and then genes. Five of these six elements comprise the chemical components of DNA, the exception being sulfur. [148][149][150] For most of its existence, Earth's habitable environment has been dominated by microorganisms and subjected to their metabolism and evolution. [152][153][154] Under certain test conditions, life forms have been observed to thrive in the near-weightlessness of space[155][156] and to survive in the vacuum of outer space. 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. Variations of this definition include Stuart Kauffman's definition as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle. This interplay between organisms and their environment is an inherent feature of living systems.[147]. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. [94] 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. Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. [125], All known life forms share fundamental molecular mechanisms, reflecting their common descent; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. [221] The moment of extinction is generally considered the death of the last individual of that species. The fungi were originally treated as plants. [162] In August 2014, scientists confirmed the existence of life forms living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. ", "Stability or stasis in the names of organisms: the evolving codes of nomenclature", "Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya", "The new higher level classification of eukaryotes with emphasis on the taxonomy of protists", "A higher level classification of all living organisms", "Thinking of biology: toward a theory of cellularity—speculations on the nature of the living cell", "From Single Cells to Multicellular Organisms", "Genetic Flip Helped Organisms Go From One Cell to Many", "General Principles of Cell Communication", "Venus, Mars, and the Ices on Mercury and the Moon: Astrobiological Implications and Proposed Mission Designs", "Why We're Looking for Alien Life on Moons, Not Just Planets", "Icy moons of Saturn and Jupiter may have conditions needed for life", "Habitability: the point of view of an astronomer", "The Galactic Habitable Zone and the age distribution of complex life in the Milky Way", "Engineering life through Synthetic Biology", "Crossing Over: How Science Is Redefining Life and Death", "Major patterns in the history of carnivorous mammals", "Oldest 'microfossils' raise hopes for life on Mars", "Geological Team Lays Claim to Oldest Known Fossils", Resources for life in the Solar System and in galaxy, and the potential scope of life in the cosmological future, "The Adjacent Possible: A Talk with Stuart Kauffman", Archaeal Richmond Mine acidophilic nanoorganisms, https://en.wikipedia.org/w/index.php?title=Life&oldid=1002671885, Short description is different from Wikidata, Wikipedia pages semi-protected against vandalism, Creative Commons Attribution-ShareAlike License, This page was last edited on 25 January 2021, at 15:28. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the universe, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. [170] They excel at exploiting uncommon sources of energy. [205] In January 2016, scientists reported that, about 800 million years ago, a minor genetic change in a single molecule, called GK-PID, may have allowed organisms to go from a single cell organism to one of many cells. The DNA backbone is resistant to cleavage, and both strands of the double-stranded structure store the same biological information. [159][160] 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,[159][161] as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. Since they are present in living things these building blocks are called biomolecules. [145][146], The diversity of life on Earth is a result of the dynamic interplay between genetic opportunity, metabolic capability, environmental challenges,[147] and symbiosis. While all organisms are composed of nearly identical molecules, evolution has enabled such microbes to cope with this wide range of physical and chemical conditions. [181], 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. 3. From a physics perspective, living beings are thermodynamic systems with an organized molecular structure that can reproduce itself and evolve as survival dictates. After death, the remains of an organism re-enter the biogeochemical cycle. [202] In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination. [140][141][142][143], In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. This system is able to regulate and control metabolism and energy supply and contains at least one subsystem that functions as an information carrier (genetic information). Most of these are synthesized by the ribosomes through an enzyme-catalyzed process called protein biosynthesis. [165][166] The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland[110] and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia. Characterization of the structure and metabolic diversity of microbial communities in such extreme environments is ongoing.
Luke Sanders Football, Car Crash In Florida Today, Dosido Strain Yield, Best Boom Arm For Blue Yeti Reddit, Mulk Raj Anand Untouchable Themes, Unh Nurse Practitioner Program, Plantur 39 Tonic Boots, We Are The Universe Experiencing Itself Reddit,