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词条 Earliest known life forms
释义

  1. Overview

  2. Earliest life forms

  3. Gallery

  4. See also

  5. References

  6. External links

{{For|the origin of life|Abiogenesis|Astrobiology|Biogenesis|Panspermia}}{{About|things that were once living|other uses|Lifeform (disambiguation)|longest lifespans|List of longest-living organisms}}{{short description|Putative fossilized microorganisms found in hydrothermal vent precipitates}}

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;[5][6] 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][9][10] The earliest direct evidence of life on Earth are microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.[11][12]

Overview

A life form, or lifeform, is an entity or being that is living.[1][2]

Currently, Earth remains the only place in the universe known to harbor life forms.[3][4]

More than 99% of all species of life forms, amounting to over five billion species,[5] that ever lived on Earth are estimated to be extinct.[6][7]

Some estimates on the number of Earth's current species of life forms range from 10 million to 14 million,[8] of which about 1.2 million have been documented and over 86 percent have not yet been described.[9] However, a May 2016 scientific report estimates that 1 trillion species are currently on Earth, with only one-thousandth of one percent described.[10] The total number of DNA base pairs on Earth is estimated at 5.0 x 1037 with a weight of 50 billion tonnes.[11] In comparison, the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon.[12] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.[13]

The Earth's biosphere can be considered sort of a shell around the earth, extending down to at least {{convert|12|mi|km|order=flip|abbr=on}} below the surface of the earth, and extending up to at least {{convert|40|mi|km|order=flip|abbr=on}} into the atmosphere.[14][15][16]

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[17][18] and to survive in the vacuum of outer space.[19][20] Life forms appear to thrive in the Mariana Trench, the deepest spot in the Earth's oceans, reaching a depth of {{convert|11034|m|ft mi|0|abbr=on}}.[21][22][23] Other researchers reported related studies that life forms thrive inside rocks up to {{convert|580|m|ft mi|abbr=on}} below the sea floor under {{convert|2590|m|ft mi|abbr=on}} of ocean, off the coast of the northwestern United States,[22][24] as well as {{convert|2400|m|ft mi|abbr=on}} beneath the seabed off Japan.[25] In August 2014, scientists confirmed the existence of life forms living {{convert|800|m|ft mi|abbr=on}} below the ice of Antarctica.[26][27]

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 {{convert|4.8|km|mi|abbr=on}} deep underground, including {{convert|2.5|km|mi|abbr=on}} below the seabed, according to a ten-year Deep Carbon Observatory project.[28][29][30][31]

According to one researcher, "You can find microbes everywhere — [they are] extremely adaptable to conditions, and survive wherever they are."[22]

Earliest life forms

Fossil evidence informs most studies of the origin of life. The age of the Earth is about 4.54 billion years;[32][33][34] the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.[35][36][37] 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.[38][39][40][41] Nonetheless, life may have started even earlier, at nearly 4.5 billion years ago, as claimed by some researchers.[42][43]

"Remains of life" have been found in 4.1 billion-year-old rocks in Western Australia.[62]

Evidence of biogenic graphite,[45] and possibly stromatolites,[46][47][48] 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.[49][50] This complements the November 2013 publication that microbial mat fossils had been found in 3.48 billion-year-old sandstone in Western Australia.[51][52][53]

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.[54][55]

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.[56][57]

According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth … then it could be common in the universe."[58][59][60]

{{clear}}

Gallery

{{LifeOnEarth}}

See also

{{div col}}
  • {{annotated link|Abiogenesis}}
  • {{annotated link|Astrobiology}}
  • {{annotated link|Extraterrestrial life}}
  • {{annotated link|Extremophile}}
  • {{annotated link|Geyserite}}
  • {{annotated link|Hypothetical types of biochemistry}}
  • {{annotated link|Life}}
  • {{annotated link|List of longest-living organisms}}
  • {{annotated link|Last universal common ancestor}}
  • {{annotated link|Oldest dated rocks}}
  • {{annotated link|Organism}}
  • {{annotated link|Outline of biology}}
  • {{annotated link|Outline of life forms}}
  • {{annotated link|Panspermia}}
  • {{annotated link|Planet Simulator}}
  • {{annotated link|Timeline of the evolutionary history of life}}
  • {{annotated link|Zircon}}
{{div col end}}

Categories

  • Terminology of biology

References

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57. ^{{cite news |author=Staff, Lawrence Berkeley National laboratory |title=Ingredients for life revealed in meteorites that fell to Earth - Study, based in part at Berkeley Lab, also suggests dwarf planet in asteroid belt may be a source of rich organic matter |url=https://www.eurekalert.org/pub_releases/2018-01/dbnl-ifl010918.php |date=10 January 2018 |publisher=AAAS – EurekAlert |accessdate=11 January 2018}}
58. ^1 {{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=https://apnews.com/e6be2537b4cd46ffb9c0585bae2b2e51 |date=19 October 2015 |agency=Associated Press |accessdate=9 October 2018}}
59. ^{{cite news |last=Schouten |first=Lucy |date=20 October 2015 |title=When did life first emerge on Earth? Maybe a lot earlier than we thought |url=https://www.csmonitor.com/Science/2015/1020/When-did-life-first-emerge-on-Earth-Maybe-a-lot-earlier-than-we-thought |work=The Christian Science Monitor |location=Boston, Massachusetts |publisher=Christian Science Publishing Society |issn=0882-7729 |archive-url=https://web.archive.org/web/20160322214217/http://www.csmonitor.com/Science/2015/1020/When-did-life-first-emerge-on-Earth-Maybe-a-lot-earlier-than-we-thought |archive-date=22 March 2016 |dead-url=no |accessdate=9 October 2018}}
60. ^{{cite web |last=Johnston |first=Ian |title=Life first emerged in 'warm little ponds' almost as old as the Earth itself - Charles Darwin's famous idea backed by new scientific study |url=https://www.independent.co.uk/news/science/origins-life-ponds-organisms-earth-age-study-a7978906.html |date=2 October 2017 |work=The Independent |accessdate=2 October 2017 }}
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External links

  • [https://web.archive.org/web/20140715055239/http://taxonomicon.taxonomy.nl/TaxonTree.aspx?id=1&src=0 Biota] (Taxonomicon)
  • [https://web.archive.org/web/20051222163318/http://sn2000.taxonomy.nl/Main/Classification/1.htm Life] (Systema Naturae 2000)
  • [https://www.biolib.cz/en/taxon/id14772 Vitae] (BioLib)
  • Wikispecies – a free directory of life
  • [https://www.google.com/search?q=earliest+known+life+forms&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjR9YXu36HbAhXyuFkKHXUFAmkQ_AUICigB&biw=1800&bih=961 Google Images: Earliest known life forms]
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5 : Biological evolution|Earliest phenomena|Evolution|Evolutionary biology|Tree of life (biology)
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