April 2020
Vol 6, Issue 17

About The Cover

Cover image expansion

ONLINE COVER A defining feature of modern plate tectonics is the plates' gradual but steady horizontal motion. Beneath our feet, these titanic slabs of rock collide, pull apart and slide past each other, molding mountains and unleashing earthquakes that rattle the world above. But while plate tectonics is central to the evolution of Earth as we know it, scientists have been uncertain about when, exactly, this geologic process began. To determine whether the lithospheric plates experienced significant motion before the early Neoarchean period some 2.8 billion years ago, Brenner et al. extracted samples from a total of 235 magnetically oriented cores from the Honeyeater Basalt of the East Pilbara Craton, a stable block of crust in Western Australia. Since the researchers knew the ages of rocks that crystallized at different times within a single block of the crust, they were able to deduce changes in the block's latitude over millions of years. Their results provide strong evidence for a large change in the latitude of the block relative to the Earth's magnetic poles between 3.35 and 3.18 billion years ago, indicating that plate tectonics may have been well underway on Earth more than 3.2 billion years ago. [CREDIT: ALEC BRENNER, HARVARD UNIVERSITY]