Study finds ‘oldest evidence’ of Earth’s magnetic field in rocks from Greenland

Rocks uncovered from Greenland have been found to bear the “oldest evidence of Earth’s magnetic field,” according to new research.

Scientists found these rocks to be about 3.7 billion years old, and the strength of the magnetic field to be at least 15 microtesla. This was comparable to the strength of Earth’s magnetic field today, they said.

“The fact that it’s similar in strength as today’s field implies whatever is driving Earth’s magnetic field has not changed massively in power over billions of years,” said Claire Nichols, a former postdoctoral researcher at Massachusetts Institute of Technology (MIT), US, and co-author of the study published in the Journal of Geophysical Research.

The team explained that iron particles in these rocks effectively act as “tiny magnets” that can detect and record the Earth’s magnetic field. The rocks were uncovered from the Isua Supracrustal Belt in Greenland.
Previously estimated to be at least 3.5 billion years old, the lifetime of the planet’s magnetic field may now extend by another 200 million years, according to the study.

“That’s important because that’s the time when we think life was emerging,” said co-lead author Benjamin Weiss, a professor of planetary sciences, MIT. The team described their estimate as a “more accurate and reliable assessment than previous studies which used individual crystals.” “If the Earth’s magnetic field was around a few hundred million years earlier, it could have played a critical role in making the planet habitable,” said Weiss.

“The magnetic field is, in theory, one of the reasons we think Earth is really unique as a habitable planet,” said Nichols. “It’s thought our magnetic field protects us from harmful radiation from space and also helps us to have oceans and atmospheres that can be stable for long periods of time.” The findings may shed light on the planet’s early conditions that helped life take hold, the researchers said.

The Earth’s magnetic field is powered by its molten iron core, slowly churning up electric currents in a self-generating “dynamo”, and extending out and around the planet like a “protective bubble”, the team explained.
While today, the field is powered in this manner, it’s thought that the inner core had not yet formed so early in the planet’s evolution.

Therefore, the researchers said, the results also raise questions about how the ancient Earth could have powered such a robust magnetic field.

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