Life

Life, sometimes referred to as biota, is a quality that distinguishes <a href="/facts/Matter/osyc04UN">matter</a> that has <a href="/facts/Biological_process/jpHldXz2">biological processes</a>, such as <a href="/facts/Cell_signaling/6oYAVP9I">signaling</a> and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for <a href="/facts/Homeostasis/rloTGAHa">homeostasis</a>, <a href="/facts/Structure/xQDPtqDQ">organisation</a>, <a href="/facts/Metabolism/WxDrm8k5">metabolism</a>, <a href="/facts/Cell_growth/wbArMaJU">growth</a>, <a href="/facts/Adaptation/5K2gNpDB">adaptation</a>, response to <a href="/facts/Stimulus_(physiology)/aBcpBfYQ">stimuli</a>, and <a href="/facts/Reproduction/nNu0F5Dy">reproduction</a>. All life over time eventually reaches a state of <a href="/facts/Death/VJmq29qm">death</a>, and none is <a href="/facts/Immortality/nDAb6CKo">immortal</a>. Many philosophical definitions of <a href="/facts/Living_systems/dbuGWtz2">living systems</a> have been proposed, such as <a href="/facts/Self-organizing/NSGBKxUa">self-organizing</a> systems. <a href="/facts/Virus/mf88Bcbl">Viruses</a> in particular make definition difficult as they replicate only in <a href="/facts/Host_(biology)/L6mop0kh">host</a> cells. Life exists all over the Earth in air, water, and <a href="/facts/Soil/5Ddpr3QM">soil</a>, with many <a href="/facts/Ecosystem/kVE8mSmR">ecosystems</a> forming the <a href="/facts/Biosphere/P1ltA4sb">biosphere</a>. Some of these are harsh environments occupied only by <a href="/facts/Extremophile/JGk1eYCk">extremophiles</a>.
Life has been studied since ancient times, with theories such as <a href="/facts/Empedocles/C6sl6Lz6">Empedocles</a>'s <a href="/facts/Materialism/VKAovnPt">materialism</a> asserting that it was composed of <a href="/facts/Classical_element/LIzQ4aoX">four eternal elements</a>, and <a href="/facts/Aristotle/U2bDlBFW">Aristotle</a>'s <a href="/facts/Hylomorphism/sMcCdKo5">hylomorphism</a> asserting that living things have <a href="/facts/Soul/DJl01SxP">souls</a> and embody both <a href="/facts/Form_(Plato)/e0zj3JR2">form</a> and matter. <a href="/facts/Origin_of_life/BvAmLPQP">Life originated</a> at least 3.5 billion years ago, resulting in a <a href="/facts/Universal_common_ancestor/pnpExNAU">universal common ancestor</a>. This evolved into all the <a href="/facts/Species/oDg6b96r">species</a> that exist now, by way of many <a href="/facts/Extinct/24p5NP2q">extinct</a> species, some of which have left traces as <a href="/facts/Fossil/by7NzIA1">fossils</a>. Attempts to classify living things, too, <a href="/facts/Aristotle%27s_biology/jc8E4MBx">began with Aristotle</a>. Modern <a href="/facts/Taxonomy/QRvFI267">classification</a> began with <a href="/facts/Carl_Linnaeus/gy5HWkHS">Carl Linnaeus</a>'s system of <a href="/facts/Binomial_nomenclature/jgBqAhPv">binomial nomenclature</a> in the 1740s.
Living things are composed of <a href="/facts/Biochemistry/fa2pWEBp">biochemical molecules</a>, formed mainly from a few core <a href="/facts/Chemical_element/0jducgWD">chemical elements</a>. All living things contain two types of large molecule, <a href="/facts/Protein/Jxmagu3E">proteins</a> and <a href="/facts/Nucleic_acid/2tTgcI0v">nucleic acids</a>, the latter usually both <a href="/facts/DNA/nB89Iauz">DNA</a> and <a href="/facts/RNA/HxPeNfNj">RNA</a>: 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 <a href="/facts/Cell_(biology)/bLM9UQvy">cell</a> is the structural and functional unit of life. Smaller organisms, including <a href="/facts/Prokaryote/oYyvaDDH">prokaryotes</a> (bacteria and <a href="/facts/Archaea/Adxh0aHw">archaea</a>), consist of small single cells. Larger <a href="/facts/Organism/j8JkL09u">organisms</a>, mainly <a href="/facts/Eukaryote/SkwyPLMA">eukaryotes</a>, can consist of single cells or may be <a href="/facts/Multicellular/rk8QBF7o">multicellular</a> with more complex structure. Life is only known to exist on Earth but <a href="/facts/Extraterrestrial_life/arxCPFTQ">extraterrestrial life</a> is <a href="/facts/Fermi_paradox/P85yfUo0">thought probable</a>. <a href="/facts/Artificial_life/YcA6tvfe">Artificial life</a> is being simulated and explored by scientists and engineers.

Life open-in-new

Life