Earliest known life forms
The earliest known life forms on Earth are putative fossilized microorganisms found in hydrothermal vent precipitates. 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, or nearly 4.5 billion years ago according to some; 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. The earliest direct evidence of life on Earth are microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.
Some estimates on the number of Earth's current species of life forms range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. However, a May 2016 scientific report estimates that 1 trillion species are currently on Earth, with only one-thousandth of one percent described. The total number of DNA base pairs on Earth is estimated at 5.0 x 1037 with a weight of 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 trillion tons of carbon. In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth.
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.
Under certain test conditions, life forms have been observed to thrive in the near-weightlessness of space and to survive in the vacuum of outer space. 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). 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, as well as 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. In August 2014, scientists confirmed the existence of life forms living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica.
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.
Earliest life formsEdit
Fossil evidence informs most studies of the origin of life. The age of the Earth is about 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago. There is evidence that life began much earlier.
Evidence of biogenic graphite, and possibly stromatolites, were discovered in 3.7 billion-year-old metasedimentary rocks in southwestern Greenland, and described in a 2014 report published in Nature.
In March of 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. Nonetheless, life may have started even earlier, at nearly 4.5 billion years ago, as claimed by some researchers.
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. This complements the November 2013 publication that microbial mat fossils had been found in 3.48 billion-year-old sandstone in Western Australia. In July 2018, scientists reported that the earliest life on land may have been bacteria living on land 3.22 billion years ago. In May 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.
- 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
- 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
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