The earliest known life forms on

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

are believed to be

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

ized

microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...

s found in

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...

precipitates, considered to be about 3.42 billion years old. The earliest time for the

origin of life In biology, abiogenesis (from a- 'not' + Greek bios 'life' + genesis 'origin') or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothes ...

on Earth is at least 3.77 billion years ago, possibly as early as 4.28 billion years ago—not long after the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...

s formed 4.5 billion years ago, and after the

formation of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface ...

4.54 billion years ago. The earliest ''direct'' evidence of life on Earth is from microfossils of

permineralized Permineralization is a process of fossilization of bones and tissues in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue. Because of the nature of the casts, perminera ...

in 3.465-billion-year-old Australian Apex chert rocks.

Biosphere

Earth remains the only place in the

universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the univers ...

known to harbor

life Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from that which does not, and is defined by the capacity for growth, reaction to stimuli, metabolism, energy ...

. The

on Earth was at least 3.77 billion years ago, possibly as early as 4.28 billion years ago. The Earth's

biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also ...

extends down to at least below the surface, and up to at least into the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

, and includes

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

hydrothermal vents A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...

, and rock. Further, the biosphere has been found to extend at least below the ice of

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

, and includes the deepest parts of the ocean, down to rocks kilometers below the sea floor. In July 2020, marine biologists reported that

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

s (mainly), in " quasi-suspended animation", were found in organically-poor sediments, up to 101.5 million years old, below the seafloor in the

South Pacific Gyre __NOTOC__ The Southern Pacific Gyre is part of the Earth's system of rotating ocean currents, bounded by the Equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South America to the east. The center ...

(SPG) ("the deadest spot in the ocean"), and could be the longest-living life forms ever found. Under certain test conditions, life forms have been observed to survive in the vacuum of outer space. More recently, in August 2020,

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

were found to survive for three years in

outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...

, according to studies conducted on the

International Space Station The International Space Station (ISS) is the largest Modular design, modular space station currently in low Earth orbit. It is a multinational collaborative project involving five participating space agencies: NASA (United States), Roscosmos ( ...

. The total mass of the

has been estimated to be as much as 4 trillion tons of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

. According to one researcher, "You can find

microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s everywhere – hey areextremely adaptable to conditions, and survive wherever they are." Of all

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of life forms that ever lived on Earth, over five billion, more than 99% are estimated to be

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

. Some estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent remain undescribed. However, a May 2016 scientific report estimates 1 trillion species currently on Earth, with only one-thousandth of one percent described. Additionally, there are an estimated 10 nonillion (10 to the 31st power) individual

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

es (including the related virions) on Earth, the most numerous type of biological entity, which some biologists consider to be life forms.

Fossil evidence

The

age of Earth The age of Earth is estimated to be 4.54 ± 0.05 billion years This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of ...

is about 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago. Some computer models suggest life began as early as 4.5 billion years ago. 3.465-billion-year-old

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

n Apex chert rocks may once have contained

s, the earliest fossil evidence of life on Earth. Microbial mat

s have been found in 3.48 billion-year-old

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

in Western Australia. Evidence of

biogenic A biogenic substance is a product made by or of life forms. While the term originally was specific to metabolite compounds that had toxic effects on other organisms, it has developed to encompass any constituents, secretions, and metabolites of p ...

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

, and possibly

stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...

s, were discovered in 3.7 billion-year-old metasedimentary rocks in southwestern

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

. Potential "

remains Remains or The Remains may refer to: Music *The Remains (band), a 1960s American rock band *The Ramainz, originally The Remains, a Ramones tribute band Albums * ''Remains'' (Alkaline Trio album), 2007 * ''Remains'' (Annihilator album), 1997 * ' ...

of life" were found in 4.1 billion-year-old rocks in Western Australia. "Putative filamentous microfossils", possibly of

methanogen Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are c ...

s and/or methanotrophs, that lived about 3.42-billion-year-old in "a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt have been identified in

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...

Fossilized microorganisms ( microfossils) have been found in

precipitates from an ancient sea-bed in the Nuvvuagittuq Belt of Quebec, Canada. These may be as old as 4.28 billion years, the oldest evidence of life on Earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.41 billion years ago. Some researchers even speculate that life may have started nearly 4.5 billion years ago. According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth ... then it could be common in the

". The possibility that terrestrial life forms may have been seeded from outer space has been considered. In January 2018, a study found that 4.5 billion-year-old

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

s found on Earth contained liquid water along with prebiotic complex organic substances that may be ingredients for

. As for life on land, in 2019 scientists reported the discovery of a

ized

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

, named ''

Ourasphaira giraldae ''Ourasphaira giraldae'' is an extinct process-bearing multicellular eukaryotic microorganism. Corentin Loron argues that it was an early fungus. It existed approximately a billion years ago during the time of the transition from the Mesoprotero ...

'', in the

Canadian Arctic Northern Canada, colloquially the North or the Territories, is the vast northernmost region of Canada variously defined by geography and politics. Politically, the term refers to the three territories of Canada: Yukon, Northwest Territories and ...

, that may have grown on land a billion years ago, well before

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

s are thought to have been living on land. In July 2018, scientists reported that the earliest life on land may have been

3.22 billion years ago. In May 2017, evidence of microbial life on land may have been found in 3.48 billion-year-old geyserite in the Pilbara Craton of Western Australia.

Genomic evidence

By comparing the genomes of modern organisms (in the domains

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

and

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...

), it is possible to infer the existence and age of the last universal common ancestor (LUCA), and a minimal set of genes. A

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...

model suggests that the LUCA may have lived 4.477 to 4.519 billion years ago, within the

Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid materia ...

eon.

Gallery

File:Stromatolites in Sharkbay.jpg,

Stromatolite Stromatolites () or stromatoliths () are layered sedimentary formations ( microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). T ...

s may have been made by

s moving upward to avoid being smothered by

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

. File:Stromatolites.jpg,

s left behind by

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

are one of the oldest fossils of life on Earth. File:Cyanobacterial-algal mat.jpg, The cyanobacterial-algal mat, salty lake on the White Sea seaside File:PIA24374-Mars-SearchForLife-LakeSaldaTurkey-20210127.jpg ,

Microbialite Microbialite is a benthic sedimentary deposit made of carbonate mud (particle diameter < 5 μm) that is formed with the mediation of microbes. The constituent carbonate mud is a type of

s in the Lake Salda rocks of

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...

File:Runzelmarken.jpg, Wrinkled Kinneyia-type sedimentary structures formed beneath cohesive microbial mats in peritidal zones. File:Kinneyia Grimsby Silurian Niagara Gorge.jpg, ''Kinneyia''-like structure in the Grimsby Formation (Silurian) exposed in Niagara Gorge, NY

Footnotes

References

External links

Vitae
(BioLib)
Biota
(Taxonomicon)

(Systema Naturae 2000) *

Wikispecies Wikispecies is a wiki-based online project supported by the Wikimedia Foundation. Its aim is to create a comprehensive open content catalogue of all species; the project is directed at scientists, rather than at the general public. Jimmy Wale ...

– a free directory of life
Google Images: Earliest known life forms

Life in the Universe
– Stephen Hawking (1996) * – Gary Ruvkun, 2019. {{DEFAULTSORT:Life form Biological evolution Biology terminology Earliest phenomena Evolution *