Epoch· The columns of time

Paleocene

66 Ma → 56 Ma

Ten million years in an emptied world: the survivors of the asteroid grow large fast, and the epoch ends in the sharpest carbon spike of the Cenozoic.

What the evidence shows

It opens on the iridium layer, in the northern spring, a season readable in the bones of fish killed the day the asteroid struck. 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 runs well ahead of brain size, and the first large mammals are brawny before they are clever. The end comes at 56 million years, when more than ten thousand billion tonnes of carbon enter the ocean and the air over a few thousand years, mostly from volcanism along the opening North Atlantic, and the surface of the sea grows more acid.

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, which is to say on the event rather than on a round number, and the size of the carbon release behind that excursion is a model result, spanning a wide range even where the boron isotopes point firmly at volcanism as the main source.

Sources

1. Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
2. During et al. (2022), Nature · The Mesozoic terminated in boreal spring
3. Bertrand et al. (2022), Science · Brawn before brains in placental mammals after the end-Cretaceous extinction
4. Gutjahr et al. (2017), Nature · Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum