Eon· The columns of time
Phanerozoic
539 Ma → Today
The eon of visible life, and the last twelve per cent of Earth's history. Everything a museum can display happens here, which is why the timeline is so crowded at this end and so bare everywhere else.
What the evidence shows
Its name means visible life, and it opens on the Cambrian explosion, the sharp rise in animal diversity between about 540 and 520 million years ago, in which most of the animal body plans still with us appear. The break is less clean than it looks: large fossils run back into the Ediacaran, some 571 million years, and what reads as one event was a run of radiations. What follows is no smoother. Twice the record is cut through: once at 252 million years, when an extinction emptied sea and land together in under two hundred thousand years, perhaps through a vast release of carbon from Siberian volcanism, and once at 66 million, when an asteroid ended the dinosaurs and a great deal else. Read against the three eons to its left, the whole of it occupies the last hand's breadth of the timeline.
Bounds and conventions
Its older bound is not in doubt; its name is. It says that life becomes visible here, when what becomes common is hard parts, and the eons before were full of life that simply did not fossilise.
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.
- Wood et al. (2019), Nature Ecology & Evolution · Integrated records of environmental change and evolution challenge the Cambrian Explosion
- Shen et al. (2011), Science · Calibrating the end-Permian mass extinction
- Schulte et al. (2010), Science · The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary