The Pilbara craton, in the Pilbara region of Western Australia, is the best-preserved remnant of Earth’s ancient continental crust (see figure 1a). It formed during the Archean eon 4 billion to 2.5 billion years ago. At that time, Earth is believed to have had a water-covered primordial crust that was more or less a single, continuous shell around the mantle. Eventually, the primordial crust transformed into continental crust, which was later joined by its thinner and denser cousin, oceanic crust.
Most present-day oceanic crust is at most 200 million years old, and its formation is ongoing and well understood: When a gap opens between tectonic plates, magma bubbles up into the gap, cools, and spreads out from the initial ridge. Continental crust is much older; three-quarters of the present-day landmass worldwide formed in the Archean as did the Pilbara craton. Because the continents have been around so long, figuring...
