Harvard geoscientists announced on Mar. 31 the discovery of the oldest direct evidence of tectonic plate movement, dating back about 3.5 billion years. The findings were published in Science and reveal that early Earth experienced plate movements, though not necessarily in the same way as seen today.
This research provides new insight into a fundamental question about Earth’s history: when did continental and oceanic plates begin to drift? Understanding this timing is important because tectonic activity has shaped land masses, formed oceans, and influenced climates and habitats that allowed life to evolve.
Lead author Alec Brenner said, “With this study, we’re able to say 3.5 billion years ago, we can see plates moving around on the Earth surface.” The team collected over 900 rock samples from more than 100 sites in the Pilbara Craton region of Western Australia—one of the world’s oldest well-preserved geological formations containing rocks from the Archean Eon.
Professor Roger Fu led research efforts using paleomagnetism to analyze ancient mineral grains for their magnetic signals. This method allows scientists to infer both orientation and latitude at which rocks formed billions of years ago. Fu said, “Almost everything unique about the Earth has something to do with plate tectonics at some level.” By examining these ancient rocks spanning a period just after 3.5 billion years ago, researchers found that part of East Pilbara shifted significantly in latitude over several million years while also rotating clockwise by more than 90 degrees.
The study compared these findings with those from South Africa’s Barberton Greenstone Belt and observed different patterns of drift between regions during similar time intervals. While ruling out a stagnant lid model (a single unbroken global plate), researchers could not yet determine which form—sluggish or episodic—the early movements took.
Brenner said, “We’re seeing motion of tectonic plates, which requires that there were boundaries between those plates and that the lithosphere wasn’t some big, unbroken shell across the globe.” Additionally, Fu noted evidence for an ancient geomagnetic reversal roughly 3.5 billion years ago: “It’s not by itself conclusive but it suggests that maybe the dynamo was in a slightly different regime than today.” The team plans further studies to clarify how modern-style plate tectonics developed.
