the.com/cambrian explosion

means A geologically sudden burst (roughly 540 million years ago) in which most major animal body-plan groups appear in the fossil record within a narrow window of time.

from Named for Cambria, the Latin name for Wales, where rock layers of this age were first studied and classified in the early 1800s by geologist Adam Sedgwick. 'Explosion' isn't a literal blast — it's a later nickname for how abrupt the diversification looks in the fossil record, especially after discoveries like Canada's Burgess Shale revealed how many strange, short-lived body plans showed up at once.