Ancient rocks reveal early plate motions.

The movement of tectonic plates—massive slabs of rock—over Earth's surface controls the planet's habitability by sustaining the carbon cycle that regulates the climate and stabilizes liquid water at the surface (1). It also facilitates efficient planetary heat loss, thereby maintaining convection in Earth's core and the generation of a magnetic field. The presence of a magnetosphere—a space around Earth dominated by its magnetic field—provides shielding from solar and cosmic radiation and mediates the loss of atmospheric gas into space (1). Deciphering plate motions in Earth's early history can thus hint at how the planet looked several billion years ago. On page 1278 of this issue, Brenner et al. (2) report differential plate motion 3.5 billion years (Ga) ago by recovering ancient magnetic field records from rocks in Australia. This may provide clues to the nature of early tectonic motions and their role in sustaining habitable conditions. [ABSTRACT FROM AUTHOR]