Geoscientists have made a groundbreaking discovery by analyzing magnetic signals in 3.5 billion-year-old rocks in Western Australia. This research reveals the oldest direct evidence of global shifts in the Earth’s outer shell, pushing the origins of plate motion back into the planet’s early history.
Hadean Earth. Image credit: Alec Brenner.
“A wide range of ages has been proposed for tectonic activity,” said Dr. Alec Brenner, a researcher from Yale University.
“Our findings confirm that tectonic plates were actively moving on Earth’s surface 3.5 billion years ago.”
This significant study focused on the Pilbara Craton in Western Australia, known for its ancient and well-preserved rock formations dating back to the Archean era, a time when Earth sustained early microbial life and endured significant asteroid impacts.
The Pilbara region hosts some of the earliest signs of life, including stromatolites and microbial rocks formed by single-celled organisms like cyanobacteria.
The research team analyzed over 900 rock samples from more than 100 sites within the Arctic Dome region.
Using an electric drill with a hollow bit and diamond teeth, they extracted cylindrical core samples while cooling them with a hand-pumped horticultural sprayer.
An instrument equipped with a compass and goniometer was inserted into the drilled holes to accurately record the orientation of the samples.
The scientists then sliced the cores into thin sections and placed them into a magnetometer capable of detecting magnetic signals 100,000 times weaker than a typical compass needle.
These samples were measured multiple times while subjected to temperatures up to 590 degrees Celsius until the magnetite mineral lost its magnetization.
“We took a significant risk; demagnetizing thousands of cores took years. But it paid off—our results exceeded our expectations!” exclaimed Dr. Brenner.
In ferromagnetic minerals, the orientation of electrons acts like a compass needle pointing towards the magnetic poles, providing clues about the rock’s geographical position relative to these poles when they formed.
By analyzing a succession of rocks spanning 30 million years, the authors observed a shift of tectonic plates in the East Pilbara Formation, moving from 53 degrees to 77 degrees latitude and rotating clockwise by over 90 degrees at rates of tens of centimeters per year.
Because the magnetic poles can reverse, it remains uncertain whether this movement took place in the northern or southern hemisphere.
Movement slowed significantly within the following 10 million years, followed by a period of relative stability.
To compare these findings with Archean sites elsewhere, the researchers analyzed the Barberton Greenstone Belt in modern-day South Africa.
Previous paleomagnetic studies have indicated that the Barberton site is near the equator and remained nearly stationary during this period, suggesting differing drift patterns between these regions.
In contemporary times, the North American and Eurasian plates are moving apart at a rate of about 2.5 cm per year.
Many questions about the timing and nature of Earth’s current plate tectonics remain unanswered, with geophysicists referring to this as the “active lid,” as opposed to earlier theories of a stagnant, sluggish, or ephemeral lid.
This research dismisses the concept of a stagnant lid but doesn’t conclusively determine which model of plate movement is most probable.
“We’re examining tectonic plate movements, which require defined boundaries between plates, contrary to the notion of a continuous, crackless lithosphere,” Brenner explained.
“Instead, the lithosphere was segmented into various parts capable of moving relative to one another.”
Additionally, Brenner and his collaborators identified the oldest known geomagnetic reversals, where a planet’s magnetic field alternates its polarity. After such a reversal, a compass needle points south instead of north.
This phenomenon is associated with dynamo action in the Earth’s core, where molten iron’s convection creates electrical currents and magnetic fields. The last known reversal occurred about 780,000 years ago.
“New evidence suggests that geomagnetic reversals were less frequent 3.5 billion years ago compared to today,” noted Roger Hu, a professor at Harvard University.
“While not definitive, it implies that the mechanisms behind these reversals may have operated differently back then.”
The findings were published in the journal Science on March 19.
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Alec R. Brenner et al. 2026. Relative plate motion and paleomagnetic detection of a core dynamo with a rare reversal at 3.5 Ga. Science 391 (6791): 1278-1282; doi: 10.1126/science.adw9250
Source: www.sci.news
