Earth is estimated to be 4.5 billion years old, but understanding when it evolved from a sizzling hot ball to a planet that could host life is a little more difficult.
Part of that puzzle has to do with plate tectonics, which are crucial to every aspect of our planet. The world’s oceans and continents sit on 15 different blocks of crust that move and shift.
While we largely think of them as responsible for creating mountains and earthquakes, the movement of these plates also contributed to creating environments with the right conditions to support life, chemically and physically.
Now researchers believe that plate tectonics were actively moving around on Earth as early as 3.2 billion years ago, which suggests an early evolution of our planet, according to a new study.
Researchers have debated over the years about when plate tectonics became active, arguing over a timescale from 1 million to 4 million years ago. The reason it’s difficult to find a clear-cut answer is because rocks containing information that old don’t exist anymore or they’ve been largely changed by their environment.
Doctoral student Alec Brenner and Assistant Professor Roger Fu, both in Harvard University’s Department of Earth and Planetary Sciences, sought out samples of rock older than 3 billion years old in Western Australia.
“Studying this problem is complicated by the rarity of rocks that formed more than 3 billion years ago, which today represent less than about 5 percent of Earth’s surface,” Brenner said in a press call on Tuesday.
They took inch-wide core samples from the 3.2-billion-year-old Honeyeater Basalt, lava rocks that still retain information about Earth’s magnetic field. The Honeyeater Basalt is a portion of the East Pilbara Craton, a stable, thick and primordial piece of Earth’s crust.
This craton is 300 miles across and formed around 3.5 billion years ago.
The researchers used the quantum diamond microscope, or QDM, at Harvard to study the samples. This study is one the first uses of the newly developed magnetometer technology for geosciences, Fu said during the press call.
The QDM provides context for the age of the magnetic minerals in the rocks.
“We are approaching this debate with paleomagnetism,” Brenner said. “And the premise is that rocks can record information about the direction of the local magnetic field where they form and, on the Earth’s surface, this direction is directly related to latitude. So by measuring the magnetizations of some of the oldest rocks on Earth, we can get a sense of where those rocks formed and then piece together the tectonic motions of blocks of crust over time in the deep past.”
In this case, the researchers were able to look at the record of the magnetic field in 235 different samples from the rock. Together, they showed that this part of the Earth’s crust drifted about 2.5 centimeters per year 3.2 billion years ago.
“It’s very comparable to the speeds of plate motion that we can see happening on the modern Earth,” Brenner said. “It’s also the oldest example that we know of in which a piece of Earth’s crust drifted long distances over the surface.”
The study published Wednesday in the journal Science Advances.
Early conditions on Earth
This suggests that early Earth was more similar to the one we know today. This means that early life on Earth, meaning single-celled organisms, had a more stable, moderate environment than previously believed.
When these plates move, they not only form ocean basins and mountain ranges. They also expose different rocks to Earth’s atmosphere, which releases chemicals and causes reactions.
These reactions likely helped stabilize Earth’s surface temperature over a time period of billions of years, the researchers said. And that allowed life to evolve.
“We’re trying to understand the geophysical principles that drive the Earth,” Fu said. “Plate tectonics cycles elements that are necessary for life into the Earth and out of it.”
The researchers noted in their study that they weren’t entirely able to rule out another possibility for the drift they measured, called true polar wander. It’s a shift in the planet’s geographical poles relative to Earth’s surface that can also cause the surface to move. But the researchers felt that their results aligned more with plate tectonic motion because of the time intervals.
This understanding of plate tectonics could be applied to other planets outside of our solar system as well. As of right now, Earth is the only planet we know of with plate tectonics.
“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,” Brenner said. “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.”