Earliest known life forms

The earliest known life forms on Earth are putative fossilized microorganisms found in hydrothermal vent precipitates.[1] The earliest time that life forms first appeared on Earth is unknown. They could have lived earlier than 3.77 billion years ago, possibly as early as 4.28 billion years ago,[1] or nearly 4.5 billion years ago according to some;[3][4] in any regards, not long after the oceans formed 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.[1][2][5][6] The earliest direct evidence of life on Earth are microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.[7][8]

Champagne vent white smokers
Evidence of possibly the oldest forms of life on Earth have been found in hydrothermal vent precipitates.[1][2]

Overview

A life form, or lifeform, is an entity or being that is living.[9][10]

Currently, Earth remains the only place in the universe known to harbor life forms.[11][12]

More than 99% of all species of life forms, amounting to over five billion species,[13] that ever lived on Earth are estimated to be extinct.[14][15]

Some estimates on the number of Earth's current species of life forms range from 10 million to 14 million,[16] of which about 1.2 million have been documented and over 86 percent have not yet been described.[17] However, a May 2016 scientific report estimates that 1 trillion species are currently on Earth, with only one-thousandth of one percent described.[18] The total number of DNA base pairs on Earth is estimated at 5.0 x 1037 with a weight of 50 billion tonnes.[19] In comparison, the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon.[20] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.[21]

The Earth's biosphere can be considered sort of a shell around the earth, extending down to at least 19 km (12 mi) below the surface of the earth, and extending up to at least 64 km (40 mi) into the atmosphere.[22][23][24]

At and below the surface of the earth, the biosphere includes soil, hydrothermal vents, and rock. It includes the deepest parts of the ocean.

Under certain test conditions, life forms have been observed to thrive in the near-weightlessness of space[25][26] and to survive in the vacuum of outer space.[27][28] Life forms appear to thrive in the Mariana Trench, the deepest spot in the Earth's oceans, reaching a depth of 11,034 m (36,201 ft; 7 mi).[29][30][31] 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,[30][32] as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan.[33] In August 2014, scientists confirmed the existence of life forms living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica.[34][35]

In December 2018, researchers announced that considerable amounts of life forms, including 70% of bacteria and archea on Earth, comprising up to 23 billion tonnes of carbon, live at least 4.8 km (3.0 mi) deep underground, including 2.5 km (1.6 mi) below the seabed, according to a ten-year Deep Carbon Observatory project.[36][37][38][39]

According to one researcher, "You can find microbes everywhere — [they are] extremely adaptable to conditions, and survive wherever they are."[30]

Earliest life forms

Fossil evidence informs most studies of the origin of life. The age of the Earth is about 4.54 billion years;[40][41][42] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.[43][44][45] There is evidence that life began much earlier.

In 2017, fossilized microorganisms, or microfossils, were announced to have been discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that may be as old as 4.28 billion years old, the oldest record of life on Earth, suggesting "an almost instantaneous emergence of life" (in a geological time-scale sense), after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.[1][2][5][6] Nonetheless, life may have started even earlier, at nearly 4.5 billion years ago, as claimed by some researchers.[3][4]

Porous chondriteIDP
Studies suggest that life on Earth may have come from biological matter carried by space dust[46] or meteorites.[47]

"Remains of life" have been found in 4.1 billion-year-old rocks in Western Australia.[48]

Evidence of biogenic graphite,[49] and possibly stromatolites,[50][51][52] were discovered in 3.7 billion-year-old metasedimentary rocks in southwestern Greenland.

In May 2017, evidence of life on land may have been found in 3.48 billion-year-old geyserite which is often found around hot springs and geysers, and other related mineral deposits, uncovered in the Pilbara Craton of Western Australia.[53][54] This complements the November 2013 publication that microbial mat fossils had been found in 3.48 billion-year-old sandstone in Western Australia.[55][56][57]

In November 2017, a study by the University of Edinburgh suggested that life on Earth may have originated from biological particles carried by streams of space dust.[46][58]

A December 2017 report stated that 3.465-billion-year-old Australian Apex chert rocks once contained microorganisms, the earliest direct evidence of life on Earth.[7][8]

In January 2018, a study found that 4.5 billion-year-old meteorites found on Earth contained liquid water along with prebiotic complex organic substances that may be ingredients for life.[47][59]

According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth … then it could be common in the universe."[48][60][61]

Gallery

Stromatolites in Sharkbay

Stromatolites may have been made by microbes moving upward to avoid being smothered by sediment.[51][52]

Stromatolites

Stromatolites left behind by cyanobacteria are one of the oldest fossils of life on Earth.

Cyanobacterial-algal mat

The cyanobacterial-algal mat, salty lake on the White Sea seaside.

Halobacteria
4000 MyaMicrobes

See also

Categories

  • Terminology of biology

References

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External links

Aluminium(II) oxide

Aluminium(II) oxide or aluminium monoxide is a compound of aluminium and oxygen with the chemical formula AlO. It has been detected in the gas phase after explosion of aluminized grenades in the upper atmosphere and in stellar absorption spectra.

Circumstellar envelope

A circumstellar envelope (CSE) is a part of a star that has a roughly spherical shape and is not gravitationally bound to the star core. Usually circumstellar envelopes are formed from the dense stellar wind, or they are present before the formation of the star. Circumstellar envelopes of the old stars (Mira variables and OH/IR stars) eventually evolve into protoplanetary nebulae, and circumstellar envelopes of the young stellar objects evolve into circumstellar discs.

Cyclopropenone

Cyclopropenone is an organic compound with molecular formula C3H2O consisting of a cyclopropene carbon framework with a ketone functional group. It is a colorless, volatile liquid that boils near room temperature. Neat cyclopropenone polymerizes upon standing at room temperature. The chemical properties of the compound are dominated by the strong polarization of the carbonyl group, which gives a partial positive charge with aromatic stabilization on the ring and a partial negative charge on oxygen. It is an aromatic compound.

Dicarbon monoxide

Dicarbon monoxide (C2O) is a molecule that contains two carbon atoms and one oxygen atom. It is a linear molecule that, because of its simplicity, is of interest in a variety of areas. It is, however, so extremely reactive that it is not encountered in everyday life. It is classified as a cumulene and an oxocarbon.

Fulminic acid

Fulminic acid is a chemical compound with a molecular formula HCNO. Its silver salt was discovered in 1800 by Edward Charles Howard and later investigated in 1824 by Justus von Liebig. It is an organic acid and an isomer of isocyanic acid, whose silver salt was discovered one year later by Friedrich Woehler. The free acid was first isolated in 1966.Fulminic acid and its salts (fulminates), for instance mercury fulminate, are very dangerous, and are often used as detonators for other explosive materials, and are examples of primary explosives. The vapors also are toxic.

Intergalactic dust

Intergalactic dust is cosmic dust in between galaxies in intergalactic space. Evidence for intergalactic dust has been suggested as early as 1949, and study of it grew throughout the late 20th century. There are large variations in the distribution of intergalactic dust. The dust may affect intergalactic distance measurements, such as to supernova and quasars in other galaxies.Intergalactic dust can form intergalactic dust clouds, known to exist around some galaxies since the 1960s. By the 1980s, at least four intergalactic dust clouds had been discovered within several megaparsec (Mpc) of the Milky Way galaxy, exemplified by the Okroy cloud.In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed as early as two billion years after the big bang, are widespread throughout the universe, and are associated with new stars and exoplanets.

Ketene

A ketene is an organic compound of the form R′R″C=C=O. Ketene also refers to the specific compound CH2=C=O, the simplest ketene molecule, which is occasionally called ethenone. Although they are highly useful, most ketenes are unstable, so they are not usually isolated during a reaction process.

Ketenimine

Ketenimines are a group of organic compounds sharing a common functional group with the general structure R1R2C=C=NR3. A ketenimine is a cumulated alkene and imine and is related to an allene and a ketene.

The parent compound is ketenimine or CH2CNH. The most recent work by Bane et al. investigates the rovibrational structure of the ν8 and ν12 bands in the high-resolution FTIR spectrum, complementing the earlier analysis of the pure rotational spectrum. This pair of Coriolis coupled bands provide a rare example where intensity sharing between bands yields sufficient intensity for an otherwise invisible band (ν12).

Methoxy group

A methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3. On a benzene ring, the Hammett equation classifies a methoxy substituent as an electron-donating group.

Methyl formate

Methyl formate, also called methyl methanoate, is the methyl ester of formic acid. The simplest example of an ester, it is a colorless liquid with an ethereal odour, high vapor pressure, and low surface tension. It is a precursor to many other compounds of commercial interest.

Methylidynephosphane

Methylidynephosphane (phosphaethyne) is a chemical compound which was the first phosphaalkyne compound discovered, containing the unusual C≡P carbon-phosphorus triple bond.

Octatetraynyl radical

Octatetraynyl radical (C8H) is an organic free radical with eight carbon atoms linked in a chain with alternating single bonds and triple bonds.

In 2007 negatively charged octatetraynyl was detected in Galactic molecular source TMC-1, making it the second type of anion to be found in the interstellar medium (after Hexatriynyl radical) and the largest such molecule detected to date.

Phosphorus mononitride

Phosphorus mononitride is an inorganic compound with the chemical formula PN. Containing only phosphorus and nitrogen, this material is classified as a binary nitride.

It is the first identified phosphorus compound in the interstellar medium.It is an important molecule in interstellar medium and the atmospheres of Jupiter and Saturn.

Photodissociation region

Photodissociation regions (or photon-dominated regions, or PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat. They occur in any region of interstellar gas that is dense and cold enough to remain neutral, but that has too low a column density to prevent the penetration of far-UV photons from distant, massive stars. A typical and well-studied example is the gas at the boundary of a giant molecular cloud. PDRs are also associated with HII regions, reflection nebulae, active galactic nuclei, and Planetary nebulae. All the atomic gas and most of the molecular gas in the galaxy is found in PDRs.

Propionaldehyde

Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is a structural isomer of acetone. It is a colorless liquid with a slightly irritating, fruity odor.

Propynal

Propynal is an organic compound with molecular formula HC2CHO. It is the simplest chemical compound containing both alkyne and aldehyde functional groups. It is a colorless liquid with explosive properties.The compound exhibits reactions expected for an electrophilic alkynyl aldehyde. It is a dienophile and a good Michael acceptor. Grignard reagents add to the carbonyl center.

Silicon monosulfide

Silicon monosulfide is a chemical compound of silicon and sulfur. The chemical formula is SiS. Molecular SiS has been detected at high temperature in the gas phase. The gas phase molecule has an Si-S bondlength of 192.93 pm, this compares to the normal single bond length of 216 pm, and is shorter than the Si=S bond length of around 201 pm reported in an organosilanethione. Historically a pale yellow-red amorphous solid compound has been reported. The behavior of silicon can be contrasted with germanium which forms a stable solid monosulfide.

Titanium oxide

Titanium oxide may refer to:

Titanium dioxide (titanium(IV) oxide), TiO2

Titanium(II) oxide (titanium monoxide), TiO, a non-stoichiometric oxide

Titanium(III) oxide (dititanium trioxide), Ti2O3

Ti3O

Ti2O

δ-TiOx (x= 0.68 - 0.75)

TinO2n−1 where n ranges from 3–9 inclusive, e.g. Ti3O5, Ti4O7, etc.

Triatomic molecule

Triatomic molecules are molecules composed of three atoms, of either the same or different chemical elements. Examples include H2O, CO2 (pictured) and HCN.

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