EARTH
The Start of Plate Tectonics
~3 billion years ago (estimates 3.8 to 2.2 Ga)
Plate tectonics, the regime in which rigid plates of the Earth's outer shell slide, dive and collide, replaced a stagnant lid, a single unbroken shell, about 3 billion years ago, with estimates from 3.8 to 2.2 billion years ago.
Plate tectonics is the regime in which the outer shell of the Earth is divided into rigid plates that slide past one another, dive beneath one another and collide. It replaced a stagnant lid over a convecting interior, that is, an interior of rock that slowly flows. Rocks formed between 3.2 and 2.5 billion years ago show the diagnostic marks of plate tectonics. One mark is passive margins, coastlines that subside quietly for hundreds of millions of years because no plate boundary disturbs them. Another is foreland basins, troughs that form in front of rising mountains. Another is paired metamorphic belts, in which rock that was heated at low pressure lies beside rock that was buried deep and stayed cool. Such a pair is the signature of one plate descending beneath another. The magnetism recorded in cratons, the old and stable blocks of the continents, indicates that the cratons were moving independently of one another.
Why it matters
Plate tectonics builds continents, buries and recycles carbon, and keeps the climate within habitable bounds over billions of years. No other known planet has plate tectonics.
Dating & uncertaintyDisputed
The starting date of plate tectonics is one of the most durable controversies in the geosciences. Metamorphic and geochemical proxies, indirect indications read in rocks, place a global network of plates around 3 billion years ago. Other researchers accept such a network only from 2.2 billion years ago. Valley and colleagues (2026) read zircons of the Hadean, mineral grains from the Earth's first eon, as attesting subduction, the descent of one plate beneath another, and a stagnant-lid regime operating simultaneously.
Earth history as one day
08:08:2715 h 52 min before midnight
if Earth’s 4.54 billion years were compressed into a single day