How did Earth avoid a fate similar to that of Mars? Ancient rocks hold clues

Roughly 1,800 miles below our feet, liquid iron swirling in Earth’s outer core generates our planet’s protective magnetic field. This magnetic field is invisible but is vital to life on Earth’s surface because it protects the planet from the solar wind, the streams of radiation from the sun.

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

What caused the magnetic field to bounce?

According to new research from scientists at the University of Rochester, this rejuvenation occurred over a few tens of millions of years, fast on geological time scales, and coincided with the formation of Earth’s solid inner core, suggesting that the core it is probably a direct cause.

“The inner core is tremendously important,” says John Tarduno, William R. Kenan, Jr., professor of geophysics in the Department of Earth and Environmental Sciences and dean of research for Arts, Sciences and Engineering in Rochester. “Just before the inner core started to grow, the magnetic field was about to collapse, but as soon as the inner core started to grow, the field regenerated.”

In the article, published in nature communications, the researchers determined several key dates in the history of the inner core, including a more precise estimate of its age. The research provides clues about the history and future evolution of Earth and how it became a habitable planet, as well as the evolution of other planets in the solar system.

Unlocking Information in Ancient Rocks

The Earth is made up of layers: the crust, where life is located; the mantle, the thickest layer of the Earth; the molten outer core; and the solid inner core, which in turn is made up of an outermost inner core and an innermost inner core.

Earth’s magnetic field is generated in its outer core, where swirling liquid iron causes Electric flowdriving a phenomenon called geodynamo that produces the magnetic field.

Because of the relationship of the magnetic field to the Earth’s core, scientists have tried for decades to determine how the Earth’s magnetic field and core have changed over 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 the Earth’s surface contain tiny magnetic particles that block the direction and strength of the magnetic field as the minerals cool from their molten state.

To better limit the age and growth of the inner core, Tarduno and his team used a CO_two lab’s superconducting quantum interference device (SQUID) laser and magnetometer to analyze feldspar crystals in anorthosite rock. These crystals have tiny magnetic needles inside them that are “perfect magnetic engravers,” says Tarduno.

By studying the magnetism locked up 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 moment when the magnetic field began to rapidly renew itself after a collapse almost 15 million years before that. The researchers attribute the rapid renewal of the magnetic field to the formation of a solid inner core which recharged the molten outer core and restored the strength of the magnetic field.
• 450 million years ago: the time when the structure of the growing inner core changed, marking the boundary between the innermost and outermost inner core. These changes in the inner core coincide with changes at about the same time in the structure of the overlying mantle, due to tectonic plates on the surface.

“Because we constrained the age of the inner core more precisely, we were able to explore the fact that the current inner core is actually made up of two parts,” says Tarduno. “Tectonic plate movements on the Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep within the Earth in the structure of the inner core.”

Avoiding a Mars-Like Fate

Better understanding the dynamics and growth of the inner core and magnetic field has important implications, not only for uncovering Earth’s past and predicting its future, but also for unraveling ways in which other planets might form magnetic shields and sustain conditions. necessary to support life. .

Researchers believe that Mars, for example, once had a magnetic field, but the field has dissipated, leaving the planet vulnerable to solar wind and the surface without oceans. While it’s not clear whether the absence of a magnetic field would have caused Earth to suffer the same fate, “Earth certainly would have lost much more Water if the Earth’s magnetic field had not regenerated”, says Tarduno. “The planet would be much drier and very different from today’s planet.”

So in terms of planetary evolution, 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 Central core that sustains a magnetic field throughout the life, many billions of years, of a planet”.