Thursday, March 2, 2017

Earliest Known Life on Earth

A life form or lifeform is an entity or being that is living.

Earth remains the only place in the universe known to harbor life forms.

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 have not yet been described.  More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (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.

More than 99% of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct.

Fossil evidence from the Earth informs most studies of the origin of life (or abiogenesis). 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, and possibly as early as the Eoarchean Era, after geological crust started to solidify following the molten Hadean Eon.

Microbial mat fossils have been found in 3.48 billion-year-old sandstone in Western Australia. Other early physical evidence of biogenic substances includes graphite, and possibly stromatolites, discovered in 3.7 billion-year-old metasedimentary rocks in southwestern Greenland. "Remains of biotic life" have been found in 4.1 billion-year-old rocks in Western Australia.

In recent years, there have been a number of discoveries that have pushed the estimated start of abiogenesis back even earlier in time. Currently, putative fossilized microorganisms (or microfossils) were discovered in hydrothermal vent precipitates in the Nuvvuagittuq belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago. According to Stephen Blair Hedges, "If life arose relatively quickly on Earth … then it could be common in the universe."

No comments:

Post a Comment