The surface of the Earth is composed of tectonic plates that slowly move around over geologic time, creating continents and oceans, and influencing climates. But scientists have debated for decades when this shift began. Some theories suggest that Earth’s crust was a single, rigid shell before it was shattered.
A new study has uncovered the oldest evidence yet that Earth’s tectonic plates had already begun shifting around some 3.5 billion years ago, much earlier than many scientists previously thought possible. The finding rewrites a chapter of the story of how the planet became an oasis for life.
The clear signs, found by researchers in ancient rocks from Western Australia, indicate that pieces of Earth’s crust moved across the planet’s surface. This movement shows that plate tectonics, one of Earth’s main features, operated during the planet’s early history.
The research, conducted by geoscientists at Harvard University and published in Science, offers one of the clearest timetables yet for when Earth’s dynamic outer shell began moving.
New insight into Earth’s crust, mantle and outer core interactions
Lead author Alec Brenner, PhD ’24, who conducted the research in the Department of Earth and Planetary Sciences (EPS) in the Harvard University Kenneth C. Griffin Graduate School of Arts and Sciences, said, “There has been a huge range of ages suggested for timing. With this study, we’re able to say that three and a half billion years ago, we can see plates moving around on the Earth’s surface.”
The team analyzed over 900 rock samples from 100 locations in the North Pole Dome.
Scientists drilled cylindrical rock cores and then used instruments such as a compass and a goniometer to record the cylinder’s position meticulously. Back in the lab, they cut the cores into thin sections and studied them with a sensitive magnetometer. By heating the samples to 590°C, they separated magnetic signals into different time periods. The whole study lasted about 2 years.
Using paleomagnetism, they analyzed tiny magnetic signals enshrined in minerals. The signals act like a geological GPS, giving clues about where the rocks were located when they formed.
In yet another indication of substantial latitudinal and rotational tectonic drift, a study has reported that one of the oldest geological regions on Earth, the Pilbara Craton or region in Western Australia, moved from about 53° to 77° out of the equator, and rotated by more than 90 degrees over millions of years. That is a sign of active plate motion rather than a frozen surface. The movement slowed, eventually stabilizing after approximately 10 million years.
Meanwhile, rocks from South Africa stayed relatively put through that era, one sign Earth was drifting in other directions.
Oldest Magnetic Flip Ever Detected
Scientists also found the oldest known geomagnetic reversal, when Earth’s magnetic field flips, causing a compass to point south instead of north. This probably happens because metallic iron in Earth’s core flows like a dynamo, generating electric currents and magnetic fields. The most recent reversal occurred about 780,000 years ago.
Most detailed and complete record yet of Earth’s last magnetic reversal
Roger Fu, Professor of Earth and Planetary Sciences at Harvard University, said, “The new findings suggest that such reversals happened less often 3.5 billion years ago than they do today. It’s not by itself conclusive, but it suggests that maybe the dynamo was in a slightly different regime than today.”
The timing of Earth’s adoption of its modern plate tectonic system is still a subject of scientific research. Various hypothesized regimes for early Earth include a single solid plate adults (‘stagnant lid’), slow-moving plates (‘sluggish lid’), or episodically moving plates. These results discount the stagnant lid hypothesis, showing that Earth’s surface was already split into tectonic plates. But it does not yet explain which style of plate motion was dominant, suggesting more work is needed.
Journal Reference:
- Alec R. Brenner, Roger R. Fu, Bradford J. Foley, Diogo L. Lourenço, Jasmine Palma-Gomez, Zheng Gong, Sarah C. Steele, Joanna Li, David T. Flannery, Adrian J. Brown, Eben B. Hodgin. Paleomagnetic detection of relative plate motions and an infrequently reversing core dynamo at 3.5 Ga. Science, 2026; 391 (6791): 1278 DOI: 10.1126/science.adw9250