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The evolutionary history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to 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 of life as early as 4.1 to 4.28 Ga, it remains controversial due to the possible non-biological fomation of the purported fossils.) The similarities among all known present-day species indicate that they have diverged through the process of evolution from a common ancestor. It is estimated that more than 99 percent of the roughly five billion species that ever lived on Earth are now extinct, . Estimates on the number of Earth's current species range from 10-14 million, of which about 1.9 million have been named and 1.6 million documented in a central database. More recently, in May 2016, scientists estimated that 1 trillion species currently live on Earth, with only one-thousandth of a percent described.
4.5 billion years (Ga) ago