Life on Earth first appeared as early as 4.28 billion years ago, soon after ocean formation 4.41 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.Earth's current life may have descended from an RNA world, although RNA-based life may not have been the first. The mechanism by which life began on Earth is unknown, though many hypotheses have been formulated and are often based on the Miller鈥揢rey experiment. The earliest known life forms are microfossils of bacteria. In July 2016, scientists reported identifying a set of 355 genes believed to be present in the last universal common ancestor (LUCA) of all living organisms...
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