Era· The columns of time

Mesozoic

252 Ma → 66 Ma

The Mesozoic, from 252 to 66 million years ago, lies between two mass extinctions, the only division of the chart bounded at both ends by a biological crisis.

Era of one hundred and eighty-six million years lying between two mass extinctions, the only division on the chart both of whose limits correspond to a biological crisis.

What the evidence shows

It begins after the end-Permian extinction and ends at 66 million years, at the impact in what is now the Yucatan. The Chicxulub impact is among the best documented events in deep time: the crater, the ejecta layer found worldwide, the iridium anomaly and the extinction all agree. Between those two limits, dinosaurs occupy the large terrestrial body sizes for a hundred and thirty million years, more than four hundred times the duration of Homo sapiens.

Bounds and conventions

Both limits are dated more finely than most on the chart, each corresponding to an event recorded simultaneously everywhere. The usual characterisation of the era, the age of dinosaurs, describes the continental realm and accounts poorly for the marine one.