Epoch· The columns of time

Paleocene

66 Ma → 56 Ma

The Paleocene, from 66 to 56 million years ago, was ten million years in a world emptied by the impact, in which the survivors grew fast, and it closed with the sharpest carbon injection of the Cenozoic.

Epoch of ten million years in a world emptied by the impact, in which surviving lineages increase rapidly in size, and closed by the most abrupt carbon injection of the Cenozoic.

What the evidence shows

It opens on the iridium layer, in the northern spring, a season established from the bones of fish killed on the day of the impact. Fewer than ten placental lineages are reckoned to have crossed that boundary. What follows is not a slow recovery: animals the size of a rat reach the size of a bear within a few million years, and their anatomy changes about three times faster than before. Body mass precedes brain volume distinctly, so that the first large mammals are massive before they are encephalised. The epoch ends at 56 million years, when more than ten thousand billion tonnes of carbon enter the ocean and the atmosphere within a few thousand years, principally through the volcanism accompanying the opening of the North Atlantic, and the sea surface acidifies.

Bounds and conventions

It begins at the Cretaceous boundary, among the sharpest on the chart. Its top is defined on the carbon isotope excursion itself, that is, on the event and not on a round number, and the magnitude of the carbon release producing it is a model result spanning a wide range, even where boron isotopes firmly identify volcanism as the principal source.