Plate tectonics involves horizontal movements and interactions between large plates on the Earth’s surface. New research shows that the movement of tectonic plates – thought to be necessary to create a habitable planet – has not occurred on Earth for the past 3.9 billion years. Credit: University of Rochester/Michael Osadcio Photography
A study from the University of Rochester, using zircon crystals, found that plate tectonics was inactive during the period when life first appeared on Earth. Instead, a “stagnant cap” mechanism is operating, releasing heat through surface cracks. This discovery challenges the traditional belief that plate tectonics is critical to the origin of life, and has the potential to change our understanding of the conditions necessary for life on other planets.
Scientists have traveled back in time to unravel the mysteries of Earth’s early history, using tiny mineral crystals called zircons to study plate tectonics billions of years ago. Research sheds light on the conditions that existed on early Earth, revealing the complex interactions between the crust, core, and the emergence of life.
Plate tectonics allowed heat from Earth’s interior to escape to the surface, forming continents and other geological features necessary for life to emerge. Therefore, “there is an assumption that plate tectonics is essential for life,” said John Tarduno, a professor in the Department of Earth and Environmental Sciences at the University of Rochester. But new research casts doubt on this assumption.
Tarduno, Professor of Geophysics at William R. Keenan Jr., who is the lead author of the paper published in the journal. alam Studying plate tectonics 3.9 billion years ago, when scientists believe the first traces of life appeared on Earth. The researchers found that no moving tectonic plates had occurred during this time. Instead, they found, Earth was releasing heat through what is known as a stagnant mantle system. The results show that while plate tectonics is a key factor for the survival of life on Earth, it is not a prerequisite for the emergence of life on Earth-like planets.
“We found that there were no plate tectonics when life was first thought to have appeared, and no plate tectonics for hundreds of millions of years afterward,” Tarduno said. “Our data shows that while we are looking for exoplanets that harbor life, planets don’t need plate tectonics.”
Unexpected changes from zircon studies
The researchers initially did not set out to study plate tectonics.
“We study the magnetization of zircon because we study the Earth’s magnetic field,” Tarduno said.
Zircons are tiny crystals containing magnetic particles that can trap the Earth’s magnetization as zircons form. With zircon dating, researchers can construct a timeline to track the evolution of Earth’s magnetic field.
The strength and direction of the Earth’s magnetic field changes depending on the latitude. For example, the current magnetic field is stronger at the poles and weaker at the equator. Armed with information about zircon’s magnetic properties, scientists can deduce the relative latitudes where zircon formed. That is, if the efficiency of the geodynamo—the process that generates the magnetic field—is constant and the field strength changes over a period, then the latitudes at which the zircons form must also change.
But Tarduno and his team found the opposite: The zircons they studied from South Africa showed that from about 3.9 to 3.4 billion years ago, the strength of the magnetic field didn’t change, meaning latitude didn’t change either.
Since plate tectonics involves changes in latitude for different land masses, says Tarduno, “it’s very likely that plate tectonic movement didn’t happen all this time and there must be other ways to remove heat from the Earth.”
To substantiate their findings, the researchers found the same patterns in the zircons they studied in Western Australia.
“We are not saying that the zircons formed on the same continent, but they appear to have formed at the same unchanging latitudes, which strengthens our argument that no tectonic plate movement is occurring at this time,” Tarduno said.
Stagnant tectonic caps: an alternative to plate tectonics
The Earth is a heat engine, and plate tectonics is ultimately the release of heat from the Earth. But the tectonic stagnation of the mantle—which results in cracks in the Earth’s surface—is another way to allow heat to escape from a planet’s interior to form continents and other geological features.
Plate tectonics involves horizontal movements and interactions between large plates on the Earth’s surface. Tarduno and his colleagues report that the average plate from the last 600 million years has moved at least 8,500 kilometers (5,280 miles) in latitude. In contrast, stagnant mantle tectonics describes how the Earth’s outer layers behave as a stagnant mantle, with no active horizontal plate movement. Instead, the outer layers stayed in place as the planet’s interior cooled. Large plumes of molten material rising deep within the Earth’s interior can cause the outer layers to crack. Stagnant mantle tectonic movements are not as efficient as plate tectonic movements in releasing heat from the Earth’s mantle, but still lead to the formation of continents.
“Primary Earth was not a planet where everything on the surface died,” said Tarduno. Things are still happening on the surface of the earth; Our research shows that they did not occur through plate tectonics. We have at least enough of the geochemical cycles provided by the stagnant cap process to generate conditions suitable for the origin of life.”
Preserving a habitable planet
While Earth is the only planet known to experience plate tectonics, other planets like[{”attribute=””>VenusexperiencestagnantlidtectonicsTardunosays[{”attribute=””>VenusexperiencestagnantlidtectonicsTardunosays
“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 , Maurice 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.
2023-06-28 02:52:53
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