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Evolutionary history of life

The evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved since life appeared on the planet, until the present. Earth formed about 4.5 billion years (Ga) ago and evidence suggests life emerged prior to 3.7 Ga. Although there is some evidence to suggest that life appeared as early as 4.1 to 4.28 Ga this evidence remains controversial due to the non-biological mechanisms that may have formed these potential signatures of past life. The similarities among all present-day organisms indicate the presence of a common ancestor from which all known species have diverged through the process of evolution. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.9 million are estimated to have been named and 1.6 million documented in a central database to date. 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 earliest evidences of life on Earth are biogenic carbon signatures discovered in 3.7 billion-year-old metasedimentary rocks discovered in western Greenland. In 2015, "remains of biotic life" were potentially found in 4.1 billion-year-old rocks in Western Australia. In March 2017, researchers reported evidence of possibly the oldest forms of life on Earth. Putative fossilized microorganisms were discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada, that may have lived as early as 4.280 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago. According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth ... then it could be common in the universe."

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When earth first was formed, its environment was hostile-at least compared to todays environment. The beginnings of life didn't happen until millions of years after earth was first form, and began to cool. There are 4 stages to how life began to form; 1) Abiotic Synthesis- there were a bunch of little molecule that make up cells in the ecosystem of early earth that came from meteorites and volcanic eruptions. With a warm atmosphere, these molecules were colliding with each other very frequently, and eventually bonded to eachother forming the basic building blocks-called monomers- for protein, DNA and other organic molecules (carbon/hydrogen based) 2)Combination of Organic Monomers- these mini-molecules then spontaneously began to form macromolecules and the basic structures of life. 3) Protocells- these macromolecules were then held within self-sufficient sacs that promoted the growth and development them. 4) Reproduction- these cells then began to reproduce and become more complex. Reproduction sparked the beginning of hereditary patterns which was the beginning of cellular evolution-the basis of biology.

Contributed by Katherine Battey

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