Have tectonic plates changed speed over the last 3 billion years? The answer has far-reaching implications, as plate tectonics affected everything from the supply of vital nutrients for early life to the rise of oxygen. We know Earth’s interior was hotter early in its history, but did plates move faster because the hotter mantle was squishier, or did the hotter mantle contain less water, which helps mantle minerals flow, slowing plates down?

A new study, led by Dr. Jennifer Kasbohm of Yale, measured ancient magnetic fields and dated rocks from Western Australia to show that the “Pilbara Craton”—an early continent—moved at quite a clip around 2.7 billion years ago. While today’s fastest plate motion is around 12 cm (4.7 inches) per year, the Pilbara Craton moved as much as 64 centimeters (25 inches) per year.

A rare remnant of early Earth

In the Archean eon, a time far closer to the formation of our Solar System than to today, basalt oozed over what would later be Western Australia in much the same way it does in Iceland and Hawaii today. Plate tectonics was still relatively new, and continents were in the early stages of emerging from what had largely been a water world. The air was devoid of oxygen, and the most advanced life came in the form of microbial communities that are preserved today in hummocky fossils known as “stromatolites.”

“We know Earth was hotter, so does that mean mantle convection happens faster?” Kasbohm asked. “Mantle convection is the process underlying plate tectonics.”

Kasbohm and colleagues from Princeton, Yale, and MIT set out to learn about the nature of Archean plate tectonics by pairing precise data for the formation of Archean basalt lavas with measurements of Earth’s magnetic field that were frozen into these basalts as they cooled. The aim was to plot the movement and speed of Pilbara as it drifted over Earth’s surface.

Because plate tectonics has largely resurfaced our planet, rocks from the Archean are relatively rare, and most are worse off after billions of years of tectonic abuse. Pilbara, however, has escaped the heating and deformation suffered by most other Archean rocks.

“Thank goodness the Pilbara emerged unscathed from the last 4 billion years of history!” Kasbohm remarked.

Heartbreaker project

Kasbohm’s study took a decade. The rock dating and magnetic analyses were elaborate, with fourteen weeks of sampling and camping in the Australian outback in 2013 and 2014, followed by years of lab work. And all that effort left her few samples to work with.

“It was a kind of a heartbreaker project in terms of geochronology,” she told Ars.

Kasbohm needed samples containing zircon crystals for the uranium-lead dating technique, but basalt does not have the right chemistry to crystallize zircon, so she needed to find zircons in ash erupted from contemporaneous volcanoes that had settled on top of individual basalt flows. There, too, she was out of luck: Most of the zircons she found turned out later to have been blown in from older granites rather than from contemporaneous volcanic eruptions.

In the end, out of 21 ash layers between lava flows that she sampled, only four yielded relevant dates: “A lot of work with not much to show,” Kasbohm said. Yet those four dates were still precise enough to track Pilbara’s movement over four points in time.