environmental stress. And that is why a 1992 paper sent shock waves through the science community, the ripples from which continue to this day. In 1992 Christopher Chyba and Carl Sagan published a review paper on the origins (yes, plural) of life.2 Using their own and others’ research, they argued that life began, died out, and began again repeatedly on Earth before it finally took hold. This suggests a much more rapid appearance of life than would seem possible, given the processes that evolutionary
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