Early magnetic field around Earth was even stronger than previously believed

The study offers evidence of a strong early magnetic field around Earth.

Earth’s magnetic field, also known as the geomagnetic field, is the magnetic field that extends from the Earth’s interior to where it meets the solar wind, a stream of charged particles emanating from the Sun. This magnetic field is invisible but is vital for life on Earth’s surface.

Scientists understand that Earth’s magnetic field has flipped its polarity many times over the millennia. Shedding light on its importance, the knowledge can provide clues to understanding the future evolution of Earth, as well as the evolution of other planets in the solar system.

A new study by the University of Rochester, scientists found that the magnetic field that first formed around Earth was even stronger than previously believed. This revelation could help scientists draw conclusions about the sustainability of Earth’s magnetic shield and whether or not there are other planets in the solar system with the conditions necessary to harbor life.

John Tarduno, William R. Kenan, Jr., Professor of Earth and Environmental Sciences and Dean of Research for Arts, Sciences, and Engineering at Rochester, said, “This research is telling us something about the formation of a habitable planet. One of the questions we want to answer is why Earth evolved as it did, and this gives us even more evidence that the magnetic shielding was recorded very early on the planet.”

Earth’s magnetic field is generated by the motion of liquid iron in the planet’s core. Because of the location and extreme temperatures of materials in the core, scientists aren’t able to directly measure the magnetic field.

Luckily, minerals that ascent to Earth’s surface contains tiny magnetic particles that lock in the direction and intensity of the magnetic field at the time the minerals fresh from their molten state.

Scientists used new paleomagnetic, electron microscope, geochemical, and paleointensity data to date and analyze zircon crystals—the oldest known terrestrial materials—collected from sites in Australia. The zircons, which are about two-tenths of a millimeter, contain even smaller magnetic particles that lock in the magnetization of the earth at the time the zircons were formed.

Scientists initially believed Earth’s early magnetic field had a weak intensity, but this new data suggests a stronger field. But, because the inner core had not yet formed, the energetic field that originally developed 4 billion years ago must have been powered by a different mechanism, suggests scientists.

Tarduno said, “We think that mechanism is chemical precipitation of magnesium oxide within Earth. The magnesium oxide was likely dissolved by extreme heat related to the giant impact that formed Earth’s moon. As the inside of Earth cooled, magnesium oxide could precipitate out, driving convection and the geodynamo.”

“Inner Earth eventually exhausted the magnesium oxide source to the point that the magnetic field almost completely collapsed 565 million years ago.”

Tarduno said, “This early magnetic field was significant because it shielded the atmosphere and water removal from the early Earth when solar winds were most intense,” Tarduno says. “The mechanism of field generation is almost certainly important for other bodies like other planets and exoplanets.”

A leading theory, for instance, is that Mars, like Earth, had a magnetic field early on in its history. However, on Mars, the field collapsed, and, unlike Earth, Mars did not generate a new one.

“Once Mars lost its magnetic shielding, it then lost its water,” Tarduno says. “But we still don’t know why the magnetic shielding collapsed. Early magnetic shielding is significant, but we’re also interested in the sustainability of a magnetic field. This study gives us more data in trying to figure out the set of processes that maintain the magnetic shield on Earth.”

The study is published in the journal PNAS.

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