Scientists led by Michael Ackerson at the Smithsonian’s National Museum of Natural History found new evidence that plate tectonics started roughly 3.6 billion years ago. Plate tectonics is essential to the Earth’s ability to support life.
The study uses zircons, the oldest minerals ever found on Earth, to decipher the planet’s ancient past.
“We are reconstructing how the Earth changed from a molten ball of rock and metal to what we have today,” Ackerson said. “None of the other planets have continents or liquid oceans or life.”
The team tested more than 3,500 zircons which revealed the age and underlying chemistry of each zircon. The aluminum content of each zircon was also of interest. High-aluminum zircons can only be produced in a limited number of ways which allows researchers to use the presence of aluminum to deduce what may have been going on at the time the zircon formed.
After analyzing the zircons the researchers deciphered a substantial increase roughly 3.6 billion years ago. Their reasoning was that one of the few ways for high-aluminum zircons to form is by melting rocks deeper beneath the Earth’s surface.
“It’s really hard to get aluminum into zircons because of their chemical bonds,” Ackerson said. “You need to have pretty extreme geological conditions.”
Ackerson reasons that this sign that rocks were being melted deeper beneath Earth’s surface meant the planet’s crust was getting thicker and beginning to cool, and that this thickening of Earth’s crust was a sign that the transition to plate tectonics had begun.