An analysis of rocks from the Honeyeater Basalt of the East Pilbara Craton, a stable block of crust in Western Australia, provides strong evidence that Earth’s tectonic plates were already moving 3.2 billion years ago (Archean Eon).
Plate tectonics is key to the evolution of life and the development of the planet.
Today, the Earth’s outer shell consists of about 15 rigid blocks of crust. On them sit the planet’s continents and oceans.
The movement of these plates shaped the location of the continents. It helped form new ones and it created unique landforms like mountain ranges.
It also exposed new rocks to the atmosphere, which led to chemical reactions that stabilized Earth’s surface temperature over billions of years. A stable climate is crucial to the evolution of life.
“Currently, Earth is the only known planetary body that has robustly established plate tectonics of any kind,” said Alec Brenner, a graduate student in the Department of Earth and Planetary Sciences at Harvard University.
“It really behooves us as we search for planets in other solar systems to understand the whole set of processes that led to plate tectonics on Earth and what driving forces transpired to initiate it.”
“That hopefully would give us a sense of how easy it is for plate tectonics to happen on other worlds, especially given all the linkages between plate tectonics, the evolution of life and the stabilization of climate.”
To determine whether Earth’s tectonic plates experienced significant motion before the early Neoarchean period some 2.8 billion years ago, Brenner and colleagues extracted samples from a total of 235 magnetically oriented Honeyeater Basalt cores — igneous rocks that retain a record of Earth’s magnetic field at the time of their crystallization.
Since the researchers knew the ages of rocks that crystallized at different times within a single block of the crust, they were able to deduce changes in the block’s latitude over millions of years.
They found that this section of crust drifted at an average rate of at least 2.5 cm per year — a velocity comparable to plate motion rates observed today.
“Basically, this is one piece of geological evidence to extend the record of plate tectonics on Earth farther back in Earth history,” Brenner said.
“Based on the evidence we found, it looks like plate tectonics is a much more likely process to have occurred on the early Earth and that argues for an Earth that looks a lot more similar to today’s than a lot of people think.”
The findings are published in the journal Science Advances.
Alec R. Brenner et al. 2020. Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga. Science Advances 6 (17): eaaz8670; doi: 10.1126/sciadv.aaz8670