Ancient rocks hold clues to how Earth avoided a Martian-like fate

Formation of the Earth's inner core

depiction of the Earth, first without an inner core; secondly, with the beginning of the growth of an inner core, about 550 million years ago; Third, with an outer and deeper inner core, about 450 million years ago. University of Rochester researchers used palaeomagnetism to determine these two key dates in the history of the inner core, which they believe restored the planet’s magnetic field before life on Earth exploded. Credit: University of Rochester Photography/Michael Osadio

New ancient magnetic research indicates that the solid inner core of the Earth formed 550 million years ago and brought back our planet’s magnetic field.

The spinning of liquid iron in the Earth’s outer core, which lies about 1,800 miles below our feet, generates a protective magnetic field for our planet, called the magnetosphere. Although this magnetic field is invisible, it is vital to life on Earth. This is because the magnetosphere protects the planet from the solar wind – streams of radiation from the sun.

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

What caused the magnetosphere to bounce?

This renewal occurred within a few tens of millions of years according to new research by scientists at the University of Rochester. This is very fast on geological time scales and coincides with the formation of the Earth’s solid inner core, indicating that the core is likely a direct cause.

“The inner core is very important,” says John Tarduno, professor of geophysics in the Department of Earth and Environmental Sciences and dean of arts, sciences and engineering research at Rochester. “Just before the inner core started growing, the magnetic field was about to collapse, but as soon as the inner core started growing, the field was renewed.”

In the paper published on July 19, 2022 in the journal NAthor TelecomHowever, scientists have identified several key dates in the history of the inner core, including a more accurate estimate of its age. The research provides new clues about Earth’s history and future development and how it became a habitable planet, as well as the evolution of other planets in the solar system.

Earth's stratigraphic structure information chart

Earth’s layers and structure.

Unlock the information in the ancient rocks

The Earth is made up of layers: the crust where life exists; the mantle, the earth’s thick layer; The molten outer core and the solid inner core, which in turn consists of an outer inner core and a deeper inner core.

Earth’s magnetic field is created in its outer core. The circulation of liquid iron there causes electric currents, which leads to a phenomenon called geodynamo that produces the magnetic field.

Because of the relationship of the magnetic field to the Earth’s core, scientists have been trying for decades to ascertain how the Earth’s magnetic field and core changed throughout the history of our planet. They cannot directly measure the magnetic field due to the location and extreme temperatures of the materials 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 minerals cool and solidify from their molten state.

To better constrain the age and growth of the inner core, Tarduno and his team used a carbon dioxide laser and a superconducting quantum interference device (SQUID) in the lab to analyze feldspar crystals from the anorthosite rock. These crystals have tiny magnetic needles inside that are “ideal magnetic recorders,” Tarduno says.

By studying magnetism trapped in ancient crystals – a field known as palaeomagnetism – researchers have identified two important new dates in the history of the inner core:

  • 550 million years ago: The time when the magnetic field began to regenerate rapidly after a collapse approximately 15 million years before that. The researchers attribute the rapid regeneration of the magnetic field to the formation of a solid inner core that recharges the molten outer core and restores the strength of the magnetic field.
  • 450 million years ago: The time when the structure of the growing inner core changed, indicating the boundary between the inner and outer core. These changes in the inner core coincide with changes at about the same time in the upper shelf structure, due to plate tectonics at the surface.

“Because we constrained the age of the inner core more precisely, we can explore the fact that the current inner core is actually made up of two parts,” Tarduno says. “The movements of the tectonic plates on the Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep inside the earth in the structure of the inner core.”

Avoid a Martian-like fate

A better understanding of the dynamics and growth of the inner core and magnetic field has important implications, not only in revealing Earth’s past and predicting its future, but also in revealing and maintaining the conditions in which other planets might form magnetic shields. harbor life.

Researchers believe that

Mars is the second smallest planet in our solar system and the fourth planet from the sun. It is a cold, dusty desert world with a very delicate atmosphere. Iron oxide is prevalent in the surface of Mars resulting in 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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