Ancient Rocks Reveal Plate Tectonics Began 3.5 Billion Years Ago
New evidence changes what we know about early Earth. Scientists found that tectonic plates were already moving 3.5 billion years ago.The discovery comes from ancient rocks in Western Australia. Researchers from Harvard University published their findings in Science.
How Scientists Tracked Ancient Motion
The team studied rocks from the Pilbara Craton. These are among the oldest well preserved formations on Earth. They used paleomagnetism to trace plate movement. Magnetic signals locked in mineral grains act like ancient GPS markers. Therefore, researchers could estimate the rocks’ original latitude. In total, they analyzed over 900 samples from more than 100 sites. The analysis took about two years.
A Clear Shift in Position
The results show clear movement. Part of the East Pilbara formation shifted from 53 degrees to 77 degrees in latitude. It also rotated clockwise by more than 90 degrees. That drift happened over several million years. For comparison, modern plates move about 2.5 centimeters per year. “We’re able to say three and a half billion years ago, we can see plates moving around,” said lead author Alec Brenner.
Ruling Out a Still Earth
Some scientists thought early Earth had a single unbroken shell. This theory is called a “stagnant lid.” The new evidence rules that out.Instead, Earth’s outer shell was already segmented. Different pieces moved relative to each other.
A Surprise from the Magnetic Field
The team also found the oldest known geomagnetic reversal. That is when the magnetic field flips direction. The last reversal happened about 780,000 years ago. The finding suggests Earth’s core dynamo operated differently billions of years ago. This research helps answer a major question. Plate tectonics started Earth on a unique path. It shaped continents, oceans, and the conditions for life.
