How did the Earth survive? Scientists have found new clues

The Earth is the only celestial body in the universe known to mankind to have life, and it can be regarded as one of the greatest wonders in the universe.

However, hundreds of millions of years ago, the Earth experienced a potentially devastating disaster - the magnetic field almost disappeared , leaving only a pitiful 10%.

You know, one of the important reasons why there is no life on Mars is that the magnetic field of Mars has "really" disappeared and cannot be protected from the direct impact of the solar wind.

Earth's magnetic field mysteriously began to recover 550 million years ago, allowing the planet to avoid a fate similar to that of Mars , according to new research from University of Rochester scientists and collaborators.

The related research paper, titled "Early Cambrian renewal of the geodynamo and the origin of inner core structure", has been published in Nature Communications.

What causes the magnetic field to bounce?

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

However, around 565 million years ago, the magnetic field dropped to 10% of its present strength.

Fortunately, the magnetic field mysteriously "bounced" back and regained its strength just before the Cambrian explosion of multicellular life on Earth.
This "bounce" occurred over tens of millions of years -- very fast on geological timescales -- and coincides with the formation of Earth's solid inner core, suggesting that the inner core could have been a direct cause .

Figure｜The internal structure of the earth (Source: Wikipedia)

"The inner core is very important," said John Tarduno, professor of geophysics in the Department of Earth and Environmental Sciences and dean of the College of Arts, Sciences and Engineering at the University of Rochester. "Just before the inner core starts growing, the magnetic field is in a state of collapse, but once the inner core starts growing, the magnetic field regenerates."

The researchers determined several key dates in the inner core's history, including a more precise estimate of its age. The study provides clues about the history and future evolution of Earth, how it became habitable, and the evolution of other planets in the solar system.

Researchers at the University of Rochester used paleomagnetism to pinpoint these two key dates in the history of Earth's core, which they believe restored the magnetic field that existed before life exploded on Earth.

Decoding messages in ancient rocks

The Earth is the third planet from the inner to the outer part of the solar system. Its main body includes the lithosphere, mantle, molten metal outer core and solid metal inner core, and has a geomagnetic field generated by the outer core.

Figure｜Solar System (Source: Wikipedia)

Scientists have tried for decades to determine how Earth's magnetic field and core have changed throughout Earth's history because of their relationship to the core. They cannot measure the magnetic field directly due to the location and extreme temperatures of the material in the core.

Fortunately, the minerals that were moved to the Earth's surface contained tiny magnetic grains that locked the direction and strength of the magnetic field as the minerals cooled from their molten state.

To better understand the core's age and growth, the team used a carbon dioxide laser and the lab's superconducting quantum interference device (SQUID) magnetometer to analyze feldspar crystals in the rock anorthite. These crystals have tiny magnetic needles inside them, making them perfect magnetic recorders.

By studying magnetic fields locked in crystals, known as paleomagnetism, the researchers determined two new important dates in the history of the Earth's core:

1. 550 million years ago : 15 million years before this, the Earth's magnetic field nearly collapsed, and then began to rapidly renew itself. 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.

2. 450 million years ago : The structure of the growing inner core changes, and the boundary between the innermost and outermost inner cores forms. These changes in the inner core occur at about the same time as changes in the structure of the overlying mantle, due to plate tectonics at the surface.

Figure | There is no core; about 550 million years ago, the inner core began to grow; about 450 million years ago, the boundary between the outermost and innermost cores was formed.

"Because we have a more precise age of the inner core, we can explore the fact that the present-day inner core is actually made up of two parts." "Plate tectonic movements on the Earth's surface indirectly affect the core, and the history of these movements is deeply imprinted in the structure of the core," Tarduno said.

Avoiding a Mars-like fate

A better understanding of the dynamics and growth of the inner core and magnetic field has important implications , not only for revealing Earth's past and predicting its future, but also for revealing how other planets might form magnetic fields and support the conditions needed for life.

Researchers believe that taking Mars as an example, Mars once had a magnetic field, but later disappeared, making Mars vulnerable to the solar wind, resulting in the absence of oceans on the surface of Mars.

While it's unclear whether the absence of a magnetic field would lead Earth to the same fate, the researchers said, "If the Earth's magnetic field had not regenerated, the Earth would have certainly lost more water." "The Earth would have been much drier than it is now and would have been very different."

In terms of planetary evolution, this study highlights the importance of magnetic fields and the mechanisms that maintain them.

"This study really highlights the need for something like a growing core to maintain a magnetic field over the lifetime of a planet, which is billions of years," Tarduno said.

Reference Links:

https://www.nature.com/articles/s41467-022-31677-7