Paleomagnetic detection of relative plate motions and an infrequently reversing core dynamo at 3.5 Ga.

Whether early Earth had a mobile lithosphere and plate tectonics is debated. We present paleomagnetic data quantifying differential motion between lithospheric blocks at ~3.48 billion years ago (Ga). This manifested as 47 − 35 + 69 centimeters per year latitudinal motion of the East Pilbara Craton (Western Australia) across high latitudes, whereas the Barberton Greenstone Belt (South Africa) was stationary at low latitudes. Comparison of this plate motion with candidate analogs suggests either rapid collisional plate tectonics (i.e., an "active-lid") or an episodically mobile lithosphere. We also document the oldest known geomagnetic reversal at ~3.46 Ga, consistent with an axial dipolar dynamo that reversed less frequently than today's. The existence and rates of these surface and core geophysical phenomena provide geodynamic context to Earth's early geophysical and biological evolution. Editor's summary: Plate tectonics is a global recycling process that underpins most of Earth's systems. Its onset remains an open question because of sparse early geologic records. Brenner et al. collected paleomagnetic data from approximately 3.4 billion-year-old rocks in Western Australia and compared them with existing data from rocks of the same age in South Africa (see the Perspective by Nichols). They detected diverging paleolatitudes, two crustal blocks moving differently around the same magnetic pole. The rate of motion is consistent with aspects of modern plate tectonics but could reflect an earlier style. This plate motion was occurring against the backdrop of the oldest known geomagnetic reversal, which was also discovered from these data. —Angela Hessler [ABSTRACT FROM AUTHOR]