Almost every major animal body plan appeared within a geological eyeblink

Starting around 538.8 million years ago, most of the animal phyla alive today show up abruptly in the fossil record within a span of roughly 13 to 25 million years — a sliver of Earth's history. Geologist William Buckland noted the strange abruptness in the early 1800s, and Charles Darwin flagged it as a challenge to his own theory in On the Origin of Species, decades before anyone had a mechanism to explain it.

— Ulf Linnemann et al., New high-resolution age data from the Ediacaran–Cambrian boundary — Terra Nova, Vol. 31, 2019