Ancient Rocks Hold Clues to How Earth Avoided Fate Like Mars

Depiction of Earth, first without an inner core; second, with a growing inner core, about 550 million years ago; third, with the outermost and innermost core, about 450 million years ago. University of Rochester researchers used paleomagnetism to determine these two important dates in the history of the inner core, which they believe restored the planet’s magnetic field just before the explosion of life on Earth. Credit: University of Rochester Illustration / Michael Osadciw

New paleomagnetic research shows Earth’s dense core formed 550 million years ago and restored our planet’s magnetic field.

The rotating molten iron in Earth’s outer core, which lies about 1,800 miles below our feet, produces our planet’s protective magnetic field, called the magnetosphere. Although this magnetic field is invisible, it is essential for life on Earth’s surface. That’s because the magnetosphere protects the planet from the solar wind—the stream of radiation from the sun.

However, about 565 million years ago, the strength of the magnetic field dropped to 10 percent of its current strength. Then, mysteriously, the magnetic field bounced back, regaining its strength just before the Cambrian explosion of multicellular life on Earth.

What causes the magnetosphere to bounce back?

This rejuvenation occurs within a few tens of millions of years, according to new research from scientists at the University of Rochester. This is very fast on geological timescales and coincides with the formation of the Earth’s dense core, suggesting that the core is likely a direct cause.

“The inner core is very important,” said John Tarduno, William R. Kenan, Jr., Professor of Geophysics in the Department of Earth and Environmental Sciences and dean of research for Arts, Science & Engineering at Rochester. “Just before the inner core started growing, the magnetic field was at the point of collapsing, but as soon as the inner core started growing, the field was regenerated.”

In a paper published on July 19, 2022 in the journal Nnatural communication, scientists determined several important dates in the history of the deep core, including a more precise estimate of its age. This research provides new clues about the future history and evolution of Earth and how it became a habitable planet, as well as the evolution of other planets in the solar system.

Earth’s layers and structures.

Unlocking information in ancient rocks

Earth is made up of layers: the earth’s crust, where life exists; mantle, the thickest layer on Earth; liquid outer core; and a dense inner core, which, in turn, consists of an outer core and an inner inner core.

Earth’s magnetic field is generated in its outer core. The molten iron spinning there causes an electric current, driving a phenomenon called a geodynamo that produces a magnetic field.

Because of the relationship of the magnetic field to the Earth’s core, scientists have been trying for decades to determine how the magnetic field and the Earth’s core have changed throughout the history of our planet. They cannot directly measure the magnetic field due to the location and extreme temperature of the material in the core. Fortunately, minerals that rise to Earth’s surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field as the mineral cools and solidifies from its molten state.

To further limit the age and growth of the inner core, Tarduno and his team used a CO2 laser and the laboratory’s superconducting quantum interference device (SQUID) magnetometer to analyze feldspar crystals from rock anorthosites. This crystal has a tiny magnetic needle inside which is a “perfect magnetic recorder,” Tarduno said.

By studying magnetism locked in ancient crystals—a field known as paleomagnetism—the researchers determined two important new dates in the history of the inner core:

• 550 million years ago: the time at which the magnetic field began to rapidly renew itself after nearly collapsing 15 million years earlier. The researchers attribute the rapid renewal of the magnetic field to the formation of a solid inner core that recharges the liquid outer core and restores the strength of the magnetic field.
• 450 million years ago: the time at which the structure of the growing inner nucleus changes, marking the boundary between the innermost and outermost nuclei. These changes in the inner core coincided with changes around the same time in the structure of the overlying mantle, due to plate tectonics at the surface.

“Because we restricted the age of the inner core more accurately, we were able to explore the fact that the current inner core actually consists of two parts,” Tarduno said. “The tectonic movements of plates at the Earth’s surface indirectly affect the inner core, and the history of this movement is imprinted deep within the Earth in the structure of the inner core.”

Avoid destiny like Mars

A better understanding of the dynamics and growth of the inner core and magnetic field has important implications, not only in uncovering Earth’s past and predicting its future, but also in uncovering ways other planets can form magnetic shields and maintain the conditions necessary for harbor life.

Researchers believe that

Mars

Mars is the second smallest planet in our solar system and the fourth planet from the sun. This is a dusty, cold, desert world with a very thin atmosphere. Iron oxide is abundant on the surface of Mars, giving it its reddish color and its nickname "Red Planet." The name Mars comes from the Roman god of war.

” data-gt-translate-attributes=”[{” attribute=””>Mars, for example, once had a magnetic field, but the field dissipated. That left the planet vulnerable to solar wind and the surface oceanless. While it is unclear whether the absence of a magnetic field would have caused Earth to meet the same fate, “Earth certainly would’ve lost much more water if Earth’s magnetic field had not been regenerated,” Tarduno says. “The planet would be much drier and very different than the planet today.”

In terms of planetary evolution, then, the research emphasizes the importance of a magnetic shield and a mechanism to sustain it, he says.

“This research really highlights the need to have something like a growing inner core that sustains a magnetic field over the entire lifetime—many billions of years—of a planet.”

Reference: “Early Cambrian renewal of the geodynamo and the origin of inner core structure” by Tinghong Zhou, John A. Tarduno, Francis Nimmo, Rory D. Cottrell, Richard K. Bono, Mauricio Ibanez-Mejia, Wentao Huang, Matt Hamilton, Kenneth Kodama, Aleksey V. Smirnov, Ben Crummins and Frank Padgett III, 19 July 2022,

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