Era· The columns of time
Mesoarchean
3.2 Ga → 2.8 Ga
Somewhere in this era the crust may start behaving as it does today, one plate sliding beneath another and driving the machinery that builds continents.
What the evidence shows
When plate tectonics began is one of the hardest questions in the field, and it is nowhere near settled. Several lines of evidence converge on a change in the way the crust behaved between 3.2 and 2.5 billion years ago, a window that opens with this era. It reads less like a switch thrown than like a long changeover, subduction working here and there before it worked everywhere. What is at stake is not geology alone: subduction recycles carbon, builds continents, and keeps the climate within bounds over billions of years, and a planet without it is a different planet.
Bounds and conventions
Nothing in the rock marks either end of this era; 3.2 and 2.8 billion years are conveniences. What the era is best known for, the onset of plate tectonics, is not dated to them and may not be a single moment at all. The evidence is indirect, the criteria are disputed, and the answers range from four billion years to less than one.
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.
- Cawood et al. (2018), Philosophical Transactions of the Royal Society A · Geological archive of the onset of plate tectonics