From Washington Post:
For 3 billion years, life on Earth was only home to water-dwelling, single-celled organisms like bacteria. But suddenly, multicellular life ballooned, knocking over the first domino in an evolutionary cascade that would one day allow you — yes, you — to exist and think and even read stuff on the Internet.
Scientists think that until 500 million years ago, life on Earth fell victim to high-energy blasts from the sun, which at the time contained a lot more of the cell-killing gamma, ultraviolet and x-rays than it does today. The atmosphere then was too thin to fully protect our single-celled ancestors, whose DNA would have been damaged by such powerful rays. That kept them from becoming more complex.More.
Later, the heavy metal fell to the centre, producing the magnet that worked the wonders. The end.
Note: Caution advised re stories that tell us, “Scientist think,” and use grammatical fudges such as “would have been,” followed by the simple past, “kept”—creating the impression that a speculative event happened, in the way that the Mount St. Helen’s eruption happened.
See also: One random mutation powers multicellular life? “All it took was one mutation more than 600 million years ago.”
More seriously: Oldest known multicellulars are Ediacaran seaweed 555 mya
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