Earth's magnetic field first formed thanks to a magma ocean, research shows. That means more planets in the universe could have atmospheres than we thought.

For the last 1 billion years, a swirling layer of liquid metal has powered the field. Fluctuations in that layer may cause parts of the field to weaken over time.
But research shows that during its earliest few billion years, the magnetic field was powered by something else: a magma ocean deep inside Earth's core.
Other Earth-like planets outside our solar system may have similar magma oceans that could power magnetic fields.
This could mean more planets in the universe have atmospheres than we thought.
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Earth's magnetic field shields the planet from deadly and destructive solar radiation. Without it, solar winds could strip Earth of its oceans and atmosphere killing everything on the planet.

This planetary safety net has existed for at least the last 3.4 billion years. Today, it's powered by swirling liquid metal in Earth's outer core. But according to scientists, this magnetic-field-generating engine has only been running for the last 1 billion years or so. Before that, the planet's core didn't facilitate enough swirling.

So a geological mystery has lingered: What powered our magnetic field before that liquid metal layer took over?

Research published earlier this year offered a potential answer. It posited that a liquid layer called a basal magma ocean once swirled deep within the Earth and created our planet's early magnetic field.

This shield was critical to the development of life.

"We know life existed on Earth between 3.5 billion and 4 billion years ago," Lars Stixrude, the lead author of the study, told Business Insider. "Life needs a suitable environment to development, and one ingredient of that environment was a magnetic field."

Stixrude and his co-authors also suggested that if this magnetic-field-creating magma once existed deep within the Earth, it could exist in other planets outside our solar system, too. And that means they might have atmosphere-protecting shields scientists weren't previously aware of.

superearth HD219134 b NASA NASA

Different engines for different magnetic fields

Our magnetic field exists today thanks to swirling liquid nickel and iron in Earth's outer core some 1,800 miles beneath the surface. The swirl generates an electrical current that powers the field.

The magnetic field isn't static: It waxes and wanes in strength based on what's going on in the core. Last month, satellites monitoring the field noted that it has weakened by 9% over the last 200 years, due in part to a weak spot over the southern Atlantic Ocean that's grown over the last 50 years.

Earth's core, meanwhile, is a ball of molten iron 4,000 miles across. That ball houses an inner core (which is about the size of the moon) that grows with time. The growth of the inner core and the exchange of heat between the inner and outer components provides the outer core with the electrical energy needed to generate a magnetic field.

But before 1 billion years ago, Earth's inner core didn't cool fast enough to provide the outer core with the fuel needed to swirl and generate that field.

"People have flailed around trying to come up with explanation to see what produced the field first," Stixrude said.

geomagnetic field Aubert et al./IPGP/CNRS Photo library

In his team's hunt for an explanation, they performed a series of simulations to see which types of core layers could generate enough electric current to get a magnetic field going.

A molten magma ocean could get the job done, they found.

Stixrude's group suggested that the molten layer's lifespan was likely between 1 billion and 2 billion years. After that, the liquid metal in the outer core took over as the magnetic field's engine .

"We don't know for sure when that switch happened," Stixrude said.

Although it's possible that Earth was without a magnetic field during the swap, he added, the planet's ancient rock record doesn't show any obvious gaps.

Other planets could hide magma oceans

Earth's magnetic field shields its atmosphere, which does a bulk of the work in keeping out deadly solar radiation. If we lost our magnetic field, we'd eventually lose our atmosphere. The same applies to Earth-like exoplanets.

"Many planets satisfy the criterion of having a habitable temperature, but a second piece is having a magnetic field to protect the surface and atmosphere," Stixrude said.

Various planets in our solar systems generate their own magnetic fields using different engines. Mercury's field today comes from a molten iron core like Earth's (that was once true for Mars as well). But Jupiter and Saturn produce theirs via a swirling envelope of metallic hydrogen, while Uranus's and Neptune's fields are born from a fluid icy layer.

jupiter magnetic field Aylin Woodward/Business Insider

For scientists studying exoplanets, an internal magma ocean like the one Earth once had is one more option to add to that known list of magnetic-field engines. That's especially relevant for exoplanets that are closer to their host stars than Earth is, sine those planets' cores might be too hot to generate magnetic fields the way Earth's does today.

"It's much more likely that exoplanets will have magnetic fields generated in a basal magma ocean," Stixrude said.

That means there might be more planets in the universe with atmospheres and the potential for life than scientists previously thought.

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Earth's magnetic field first formed thanks to a magma ocean, research shows. That means more planets in the universe could have atmospheres than we thought.

Different engines for different magnetic fields

Other planets could hide magma oceans

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