Zircons Reveal Earth’s Early History: Life Emerged on a “Standing Cover,” Not Plate Tectonics

Plate tectonics involves the horizontal movement and interaction of the Earth’s large plates. A new study shows that mobile tectonics – thought to be essential to the formation of the planet – did not occur on Earth until 3.9 billion years ago. Credit: University of Rochester Photo / Michael Osadciw

Research from the University of Rochester, using zircon crystals, found that plate tectonics was inactive at the time when life first appeared on Earth. Instead, a “fixed cover” was working, releasing heat through cracks in the surface. This discovery challenges the traditional belief that plate tectonics is important for the origin of life, which may change our understanding of the factors necessary for life on other planets.

Scientists have gone back in time to unravel the mysteries of Earth’s history, using tiny rocks called zircons to study tectonics billions of years ago. This study sheds light on the conditions at the beginning of the Earth, revealing the complex relationship between the Earth’s crust, core, and the emergence of life.

Plate tectonics allows heat from the Earth’s interior to escape to the surface, creating continents and other structures necessary for life to emerge. Accordingly, “plate tectonics has been thought to be important for life,” says John Tarduno, who teaches in the Department of Earth and Environmental Sciences at the University of Rochester. But a new study casts doubt on that idea.

Tarduno, William R. Kenan, Jr. Professor of Geophysics, is the lead author of a paper published in the journal. Nature examining plate tectonics from 3.9 billion times ago, when scientists believe that the first signs of life appeared on Earth. The researchers found that mobile tectonics did not occur during this period. Instead, they found, Earth is emitting heat through what’s called a passive mantle. The results show that while plate tectonics is an important factor for life on Earth, it is not necessary for life to develop on a planet like Earth.

“We found that there was no tectonics when life began, and that there was no tectonics for hundreds of years afterward,” Tarduno said.

An unexpected deviation from the study of zircons

The researchers did not begin to study plate tectonics.

Tarduno said: “We were studying the magnetic force of zirconium because we were studying the magnetic force of the earth.”

Zircons are small particles that contain magnetic particles that can block the Earth’s magnetic field at the time the zircons were formed. By dating zircon, researchers can trace the direction of the Earth’s magnetic field.

The strength is how the Earth’s magnetic field changes with latitude. For example, the current’s magnetic field is strongest at the poles and weakest at the equator. By knowing the magnetic properties of zircons, scientists can calculate the latitudes where the zircons formed. That is, if the geodynamo force—the process of generating the magnetic field—is stable and the field strength changes over time, the latitude where the zircons form must also change.

But Tarduno and his team found something different: the zircons they studied from South Africa show that between 3.9 and 3.4 billion years ago, the magnetic field did not change, which means that the latitudes did not change.

Because platetectonics involves changing the latitudes of different types of land, Tarduno says, “the movement of the plates did not happen at this time and there must have been another way that the earth removed the heat.”

Further strengthening their findings, the researchers found the same patterns in zircon that they studied from Western Australia.

“We are not saying that the zircons were formed on the same continent, but it seems that they were formed on the same unaltered surface, which strengthens our argument that there was no tectonic movement occurring at this time,” says Tarduno.

Lid tectonics: an alternative to tectonics

The Earth is a heat engine, and plate tectonics is what releases heat from the Earth. But dynamic tectonics – which causes cracks in the Earth’s surface – is another mechanism that allows heat to escape from the Earth’s interior to form continents and other celestial bodies.

Plate tectonics involves the horizontal movement and interaction of the Earth’s large plates. Tarduno and his colleagues say that, on average, the plates of the last 600 million years have moved about 8,500 kilometers (5280 miles) in latitude. In contrast, stable lid tectonics describes how the outer part of the Earth behaves like a fixed lid, without horizontal plate movement. Instead, the outer layer stays in place while the Earth’s interior cools. Large clouds of molten material from the Earth’s interior can cause the outer surface to rupture. Subduction tectonics is not as effective as plate tectonics in extracting heat from the Earth, but it can lead to the formation of continents.

Tarduno said: “Early Earth was not a planet where everything was dead. “Things were still happening in the world; Our research shows that it is not done through energy consumption. “We had enough geochemical cycling provided by the barrier mechanisms to create the right conditions for the origin of life.”

Taking care of the world where people live

Although Earth is the only known planet with tectonics, other planets, such as[{” attribute=””>Venus, experience stagnant lid tectonics, Tarduno says.

“People have tended to think that stagnant lid tectonics would not build a habitable planet because of what is happening on Venus,” he says. “Venus is not a very nice place to live: it has a crushing carbon dioxide atmosphere and sulfuric acid clouds. This is because heat is not being removed effectively from the planet’s surface.”

Without plate tectonics, Earth may have met a similar fate. While the researchers hint that plate tectonics may have started on Earth soon after 3.4 billion years, the geology community is divided on a specific date.

“We think plate tectonics, in the long run, is important for removing heat, generating the magnetic field, and keeping things habitable on our planet,” Tarduno says. “But, in the beginning, and a billion years after, our data indicates that we didn’t need plate tectonics.”

Reference: “Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism” by John A. Tarduno, Rory D. Cottrell, Richard K. Bono, Nicole Rayner, William J. Davis, Tinghong Zhou, Francis Nimmo, Axel Hofmann, Jaganmoy Jodder, Mauricio Ibañez-Mejia, Michael K. Watkeys, Hirokuni Oda and Gautam Mitra, 14 June 2023, Nature.
DOI: 10.1038/s41586-023-06024-5

The team included researchers from four US institutions and institutions in Canada, Japan, South Africa, and the United Kingdom. The research was funded by the US National Science Foundation.