Cambrian explosion , proper n :
(evolutionary biology) The relatively rapid appearance, around 541 million years ago, of most major animal phyla, as demonstrated in the fossil record. English naturalist and geologist Charles Darwin’s book On the Origin of Species, considered the foundation of evolutionary biology, was published on this day in 1859.
Source http://handbookblogger.blogspot.com/2017/11/cambrian-explosion-word-of-day-for.html
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