Almost imperceptibly, the talented young politician whom most had labelled as just a bit
too upper -
crust ever to get to the very top, seemed to be changing.
On the hot young Earth, the outer layer was
too weak and soft for plate tectonics to operate until the
upper mantle cooled enough to allow sections of
crust to slip under each other, or subduct, at collision zones some 3.2 to 2.5 billion years ago.