Era· The columns of time

Paleozoic

539 Ma → 252 Ma

The Paleozoic runs from the first shelled animals, 539 million years ago, to the most severe extinction in the fossil record, 252 million years ago, and life moved onto land within it for good.

Era of two hundred and eighty-seven million years, running from the first shelled animals to the most severe extinction in the fossil record. The move onto land occurs within it and is not reversed.

What the evidence shows

It opens with the Cambrian explosion, in which most animal body plans appear within a few tens of millions of years. The name makes the boundary sharper than it is: diversification begins at the end of the Ediacaran, before the era, and continues well after its opening. Plants reach the continents around 470 million years and alter the composition of the atmosphere as much as that of soils. The era closes at 251.9 million years with the end-Permian extinction, dated to within a hundred thousand years, which removes the great majority of marine species and accounts for the following era not resembling this one.

Bounds and conventions

Both limits are golden spikes, fixed in a determined outcrop rather than on a round number, which makes this era among the best bounded on the chart. Its name belongs to another register: ancient life is a judgement formulated in the nineteenth century, when everything preceding it was still invisible.