Zircons unlock Earth’s ancient history: Life sprung from a stagnant lid, not plate tectonics

Earth's crust billions of years ago

Plate tectonics involves the horizontal movement and interaction of large plates on the earth’s surface. Shifting plate tectonics, thought to be necessary for the creation of a habitable planet, did not occur on Earth 3.9 billion years ago, new research indicates. Credit: University of Rochester illustration / Michael Osadciw

A University of Rochester study using zircon crystals found that plate tectonics was inactive during the time life first appeared on Earth. Instead, a stagnant lid mechanism was in operation, releasing heat through the surface cracks. This discovery challenges the traditional belief that plate tectonics is essential for the origin of life, potentially reshaping our understanding of the conditions necessary for life on other planets.

Scientists have traveled back in time to unravel the mysteries of Earth’s ancient history, using tiny mineral crystals called zircons to study plate tectonics billions of years ago. The research sheds light on the conditions that existed in the early Earth, revealing a complex interaction between the Earth’s crust, core and the emergence of life.

Plate tectonics allows heat from within the Earth to escape to the surface, forming continents and other geological features necessary for life to emerge. As a result, plate tectonics has been speculated to be necessary for life, says John Tarduno, a professor in the Department of Earth and Environmental Sciences at the University of Rochester. But new research questions that assumption.

Tarduno, William R. Kenan, Jr. Professor of Geophysics, is the lead author of an article published in the journal Natureexamining plate tectonics from a time 3.9 billion years ago, when scientists believe the first traces of life appeared on Earth. The researchers found that shifting plate tectonics was not occurring during this period. Instead, they found, the Earth was releasing heat through what’s known as a stagnant lid regime. The results indicate that although plate tectonics is a key factor in sustaining life on Earth, it is not a requirement for life to originate on an Earth-like planet.

We found that there was no plate tectonics when life is thought to have originated, and that there was no plate tectonics for hundreds of millions of years afterward, Tarduno says. Our data suggests that when looking for exoplanets that harbor life, the planets don’t necessarily have to have plate tectonics.

An unexpected deviation from a zircon study

The researchers had not initially set out to study plate tectonics.

We were studying the magnetization of zircons because we were studying the Earth’s magnetic field, Tarduno says.

Zircons are tiny crystals containing magnetic particles that can block the Earth’s magnetization at the time the zircons were formed. By dating the zircons, researchers can construct a timeline that traces the development of the Earth’s magnetic field.

The strength and direction of the Earth’s magnetic field change according to latitude. For example, the current magnetic field is strongest at the poles and weakest at the equator. Armed with information about the magnetic properties of zircons, scientists can infer the relative latitudes at which zircons formed. That is, if the efficiency of the geodynamic process that generates the magnetic field is constant and the field strength changes over a period, the latitude at which the zircons form must also change.

But Tarduno and his team found the opposite: The zircons they studied in South Africa indicated that during the period from about 3.9 to 3.4 billion years ago, the strength of the magnetic field did not change, which it means that the latitudes have not changed either.

Because plate tectonics includes changes in the latitudes of various land masses, Tarduno says, plate tectonic motions likely weren’t occurring during this time, and there must have been another way Earth was removing heat.

Further bolstering their findings, the researchers found the same patterns in the zircons they studied from Western Australia.

We’re not saying that the zircons formed on the same continent, but they appear to have formed at the same immutable latitude, which reinforces our argument that plate tectonic movement wasn’t occurring at the time, Tarduno says.

Stagnant Lid Tectonics: An Alternative to Plate Tectonics

The Earth is a heat engine and plate tectonics is ultimately the release of heat from the Earth. But stagnant lid tectonics, which causes cracks in Earth’s surface, is another means that allows heat to escape from the planet’s interior to form continents and other geological features.

Plate tectonics involves the horizontal movement and interaction of large plates on the earth’s surface. Tarduno and his colleagues report that, on average, the plates have moved at least 8,500 kilometers (5,280 miles) in latitude over the past 600 million years. In contrast, stagnant lid tectonics describes how the outermost layer of the Earth behaves like a stagnant lid, with no active horizontal plate motion. Instead, the outer layer stays in place while the planet’s interior cools. Large plumes of molten material originating deep inside the Earth can cause the outer layer to rupture. Lid tectonics aren’t as effective as plate tectonics at releasing heat from the Earth’s mantle, but they can still lead to the formation of continents.

Early Earth was not a planet where everything died on the surface, Tarduno says. Things were still happening on the earth’s surface; our research indicates that they simply weren’t happening through plate tectonics. We had at least enough geochemical cycles provided by the stagnant lid processes to produce suitable conditions for the origin of life.

Maintain a habitable planet

While Earth is the only known planet to experience plate 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 planets 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 didnt need plate tectonics.

Reference: Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism byJohn A. Tarduno, Rory D. Cottrell, Richard K. Bono, Nicole Rayner, William J. Davis, Tinghong Zhou, Francis Nimmo, Axel Hofmann, Jaganmoy Jodder, Mauricio Ibaez-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.

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