Era· The columns of time
Cenozoic
66 Ma → Today
The last sixty-six million years, in which mammals inherit a world emptied by an asteroid, grasslands spread, ice returns, and one primate lineage ends up drawing timelines.
What the evidence shows
It opens at the Chicxulub boundary, 66 million years ago, and what makes it possible is not mammalian superiority but vacancy: the impact removed the animals that had held the largest body sizes for most of the era before it. What follows is a long cooling, from a world with no permanent ice to one with two ice caps, and the spread of grasses that turns the interiors of continents into open country. Homo sapiens appears in the last 300,000 years of it, under half a per cent of the era.
Bounds and conventions
Only one of its bounds is fixed. The older is among the sharpest on the chart; the recent end stays open, because this is the era we are in, and whether the last few centuries have earned a division of their own is the substance of the Anthropocene debate, which the chart has so far declined to settle.
Sources
- 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.
- Schulte et al. (2010), Science · The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary
- Morgan et al. (2022), Nature Reviews Earth & Environment · The Chicxulub impact and its environmental consequences