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

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 at least 3.77 billion years ago, possibly as early as 4.28 billion years,[1] or even 4.5 billion years;[3][4] not long after the oceans formed 4.41 billion years ago, and 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]

BiosphereEdit

Currently, Earth remains the only place in the universe known to harbor life.[9][10] The Earth's biosphere extends down to at least 19 km (12 mi) below the surface,[11][12][13][14] and up to at least 64 km (40 mi) into the atmosphere,[15][16][17] including soil, hydrothermal vents, and rock, even 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica.[18][19] It includes the deepest parts of the ocean,[20][21][22] down to rocks kilometers below the sea floor.[21][23][24] According to one researcher, "You can find microbes everywhere – [they are] extremely adaptable to conditions, and survive wherever they are."[21] Under certain test conditions, life forms have been observed to survive in the vacuum of outer space.[25][26] The total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon.[27]

Of all species of life forms that ever lived on Earth, over five billion,[28] more than 99% are estimated to be extinct.[29][30] Some estimates on the number of Earth's current species range from 10 million to 14 million,[31] of which about 1.2 million have been documented and over 86 percent remain undescribed.[32] However, a May 2016 scientific report estimates 1 trillion species currently on Earth, with only one-thousandth of one percent described.[33]

Earliest life formsEdit

The age of the Earth is about 4.54 billion years;[34][35][36] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.[37][38][39] There is evidence that life began in the earlier part of this one billion year range.[3][4]

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] A 2013 publication announced the discovery of microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.[40][41][42][43] Evidence of biogenic graphite,[44] and possibly stromatolites,[45][46][47] were discovered in 3.7 billion-year-old metasedimentary rocks in southwestern Greenland, and described in 2014 in Nature. "Remains of life" were found in 4.1 billion-year-old rocks in Western Australia, and described in a 2015 study.[48]

 
The theory of panspermia suggests that life on Earth may have come from biological matter carried by space dust[49] or meteorites.[50]

A 2016 genetic study concluded that the last universal common ancestor (LUCA) may have lived in deep-sea hydrothermal vents 3.5 to 3.8 billion years ago.[51] In March 2017, fossilized microorganisms (microfossils) were announced to have been discovered in hydrothermal vent 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.[1][2][5][6] Some researchers even speculate that life may have started nearly 4.5 billion years ago.[3][4] According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth … then it could be common in the universe."[52][53][54]

As for life on land, in 2019 scientists reported the discovery of a fossilized fungus, named Ourasphaira giraldae, in the Canadian Arctic, that may have grown on land a billion years ago, well before plants were living on land.[55][56][57] In July 2018, scientists reported that the earliest life on land may have been bacteria 3.22 billion years ago.[58] 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.[59]

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.[50][60]

GalleryEdit

See alsoEdit

  • Abiogenesis – The natural process by which life arises from non-living matter
  • Astrobiology – Science concerned with life in the universe
  • Extraterrestrial life – Life occurring outside of Earth which did not originate on Earth
  • Extremophile – Organisms capable of living in extreme environments
  • Geyserite – A form of opaline silica that is often found around hot springs and geysers
  • Hypothetical types of biochemistry – Possible alternative biochemicals used by life forms
  • Life – Characteristic that distinguishes physical entities having biological processes
  • Life timeline – Life events since the formation of the Earth 4.54 billion years ago
  • List of longest-living organisms – Oldest life forms with verified ages
  • Last universal common ancestor – Last recent common ancestor of all current life
  • Oldest dated rocks – Includes rocks over 4 billion years old from the Hadean Eon
  • Organism – Any individual living physical entity
  • Outline of biology – Hierarchical outline list of articles related to biology
  • Outline of life forms – 1=Overview of and topical guide to life forms
  • Panspermia – Hypothesis that life exists throughout the Universe, distributed by space dust, meteoroids, asteroids, comets, planetoids, and also by spacecraft carrying unintended contamination by microorganisms
  • Planet Simulator – Machine designed to study life in the universe
  • Timeline of the evolutionary history of life – The current scientific theory outlining the major events during the development of life
  • Zircon – Zirconium silicate, a mineral belonging to the group of nesosilicates

Categories

ReferencesEdit

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