The Magnetic Field And Life On Earth

By Victoria Clare

Posted July 22, 2020

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Y: Okay Don, pop quiz: What did the Earth need to become habitable?

D: That's not too hard, Yaël. Let's see. It needed to be close to a star, but not too close...it needed water...a rocky surface...an atmosphere...Am I missing something?

Y: Something pretty important--a magnetic field.

D: What did that do?

Y: Scientists think it protected the early Earth's atmosphere from the sun, which was a lot more violent when the earth was still forming. For a model of exactly how violent, scientists looked to Kappa Ceti, a star that's a lot like our sun, but younger. It's about four hundred to six hundred million years old, which is about how old our sun was when life first appeared on Earth.

D: So what's Kappa Ceti like?

Y: Very magnetically active, which is normal for stars its age. It has starspots all over its surface--like sunspots on our sun, just larger and more of them--and it propels plasma into space on stellar winds that are fifty times as strong as the solar wind coming from our sun. When modeling the effect of a wind that strong on a young earth, scientists found that the Earth's protected region, called the magnetosphere, would be one‑third to one‑half as big as it is today--less protection, but enough to keep the atmosphere intact.

D: So what would have happened if the Earth didn't have a magnetic field?

Y: Well, we can look at Mars as an example of that. Without a magnetic field, it changed from a planet with briny oceans to the cold desert that it is today.

D: Tough luck, Mars.

What did the Earth need to become habitable? (NASA, Wikimedia Commons)

The Earth needed a number of things to become habitable. First of all, it needed to be close to a star, but not too close. It also needed water, a rocky surface and atmosphere.

Most important of all, however, it needed a magnetic field. Scientists think it protected the early Earth's atmosphere from the sun, which was a lot more violent when the earth was still forming. For a model of exactly how violent, scientists looked to Kappa Ceti, a star that's a lot like our sun, but younger.

It's about 400 to 600 million years old, which is about how old our sun was when life first appeared on Earth.

Kappa Cet is very magnetically active, which is normal for stars its age. It has starspots all over its surface, which are like sunspots on our sun, just larger and more numerous. It also propels plasma into space on stellar winds that are fifty times as strong as the solar wind coming from our sun.

When modeling the effect of a wind that strong on a young earth, scientists found that the Earth's protected region, called the magnetosphere, would be one-third to one half as big as it is today, just enough to keep the atmosphere intact.

We can look at Mars as an example of what would have happened if the Earth didn't have a magnetic field. Without a magnetic field, it changed from a planet with briny oceans to the cold desert that it is today.