When did plate tectonics begin on Earth? New research finds some of the earliest clues

When did plate tectonics begin on Earth? New research finds some of the earliest clues

By Marissa Grunes edited by Sarah Lewin Frasier

The colossal movements of tectonic plates shape our world, affecting the composition of Earth’s atmosphere, the planet’s protective magnetic field, and perhaps even the flourishing of life. Now scientists have compelling evidence that some form of plate tectonics may have begun as early as 3.48 billion years ago, according to a new study appearing today in Science.

Using magnetic traces from ancient parts of the Earth’s crust, the researchers found that part of what is now Western Australia drifted towards the magnetic north pole over a few million years, as part of South Africa remained stationary. It is the earliest documented case of relative plate motion by more than half a billion years, and it has implications for understanding early life on Earth and how the planet’s tectonic activity began. (Disclosure: The author of this article is integral to the research team during last year’s field season.)

The Earth today is a jigsaw of giant chunks of crust traveling across the planet, smashing together like huge bumper cars, pushing up mountain ranges and melting back into magma along their edges. All this activity, called plate tectonics, appears to be unique to our solar system. It is thought that our rocky planet neighbors instead have a continuous, solid shell.

On supporting science journalism

If you like this article, please consider supporting our award-winning journalism by subscribes. By purchasing a subscription, you help secure the future of impactful stories about the discoveries and ideas that shape our world today.

However, no one knows how or when plate tectonics started on Earth in the first place. “It’s one of the most fundamental questions in Earth science,” says study co-author Roger Fu, a Harvard University paleomagnetist. Geologists use different tools to examine the condition of the Earth’s crust over the eons, but the gold standard is evidence of relative motion: one piece of the Earth’s crust moving away from or toward another piece. Because the Earth’s magnetic field – driven by the motion of the core – is the key.

Like any magnet, the Earth has a north and south magnetic pole, roughly aligned with the globe’s geographic poles. These rods turn at irregular intervals; the last such reversal was about 780,000 years ago. (Right now, Earth’s magnetic north is technically in the southern hemisphere.) The direction and angle of the lines of force that curve between the poles are imprinted in molten rock as it solidifies on the planet’s surface, providing clues to where ancient rocks have been.

To find such traces, the team analyzed rock samples from remote parts of Western Australia and South Africa. These areas contain some of the planet’s oldest crustal pieces, called cratons, which have survived billions of years of grinding and melting processes and form the building blocks of continents.

The rock strata’s magnetic record shows that part of the craton in Australia shifted northwards over a few million years, while part of the craton in South Africa remained stationary. Such movement is intriguing because it “suggests that there is probably a plate boundary between the two (cratons),” said Michael Brown, an emeritus geologist at the University of Maryland who was not involved in the study.

Several scientists agreed that this study is about the earliest we will be able to see such results, since so few rocks remain intact from Earth’s first billion years. “It’s like having a jigsaw in a thousand pieces, but you only have 35 pieces,” says Brown. The relative motion doesn’t tell us exactly what was going on during this period, Brown adds, but it could put new constraints on the mathematical models scientists use to recreate the ancient Earth.

The findings may support another recent study, which uses ancient crystals of the mineral zircon – found in another part of Western Australia – to suggest that parts of the Earth’s crust may have melted back into the mantle around 3.35 billion years ago. Evidence from zircon crystals is notoriously difficult to interpret, and the cycling of the crust into the mantle can occur under many different circumstances. However, the process is necessary for any form of plate tectonics. In this sense, the two studies reinforce each other.

Fu’s team also found evidence of the earliest known reversal of Earth’s magnetic poles, around 3.46 billion years ago. Consistent with the evidence for relative tectonic motion, the study’s results “show that the Earth behaved very much like it does today,” according to Jun Korenaga, a Yale University geologist who was not involved in the study.

The Western Australian craton that the team studied is home to the world’s oldest confirmed fossils of single-celled organisms, dating back to about 3.48 billion years ago. Knowing the latitude of these rocks at the time could help scientists learn more about the origins of life. And understanding what kind of tectonics were operating back then can set limits on how Earth’s modern plate tectonics started. If we know what Earth’s early tectonics looked like, we can start hunting for similar behavior on other planets, which in turn could guide the search for life. “What kind of planet did life first appear on?” Fu wonders. The answer, he says, “has implications for how abundant life is likely to be in the universe.”

It’s time to stand up for science

If you liked this article, I would like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in its two-century history.

I have been one Scientific American subscriber since I was 12 years old, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does for you too.

If you subscribe to Scientific Americanyou help ensure our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten laboratories across the United States; and that we support both budding and working scientists at a time when the value of science itself is too often not recognised.

In return, you receive important news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-see videos, challenging games, and the world of science’s best writing and reporting. You can even give someone a subscription.

There has never been a more important time for us to stand up and show why science is important. I hope you will support us in that mission.