The invisible shield that protects Earth (and those living on it) from solar radiation bombardment may have disappeared 565 million years ago if not for an important change beneath the planet’s surface.
That strength is enough to maintain liquid water on earth’s surface and protect the planet from more intense exposure to the sun’s radiation.
And it’s likely due to the formation of an inner core of solid iron in a “snap” 15-million-year period.
Why does a magnetic field matter?
You can’t see Earth’s magnetic field – or magnetosphere – but thank your lucky stars it’s there.
Without it, we wouldn’t exist, and having one is considered compulsory for planets wanting to harbour life.
Earth’s strong magnetic field protects us from exposure to harmful solar radiation, letting only a small amount reach populated places.
The magnetic field is also an importance defence for earth’s electrical infrastructure – from power grids that keep the lights on, to the smartphone or computer you’re reading this article on now.
It’s also credited with keeping Earth flush with surface water.
This strong planetary shield is credited with life emerging on Earth, unlike Mars and Venus – both of which have comparatively weaker magnetospheres.
“Earth certainly would’ve lost much more water if the magnetic field had not been regenerated,” says Professor John Tarduno from Rochester University.
Rock solid: Inner core gives Earth the edge
Earth’s blessedly strong magnetic field seems to have been sustained thanks to the emergence of the planet’s solid core 550 million years ago.
Tarduno’s team was able to pinpoint these dates thanks to studies into the magnetism of ancient rocks and minerals.
Rocks that migrate to the surface over millions of years are in a locked-in magnetic state from when they first formed – allowing scientists to determine the nature of earth’s magnetic field at the time they first cooled and hardened.
This branch of science is known as palaeomagnetism, and allowed Rochester researchers to pinpoint (at least in geological terms) when the Earth’s magnetic field began to strengthen to its modern level.
Its also enabled a greater understanding of the inner core’s structure.
“The inner core is tremendously important,” Tarduno says.
“Right before the inner core started to grow, the magnetic field was at the point of collapse, but as soon as the inner core started to grow, the field was regenerated,” explains Tarduno.
It’s believed the waning strength of the magnetic field was due to heat loss in the liquid core.
But the solid iron core formed around 15 million years later, Earth’s magnetic strength was restored – a moment that appears integral to our ancestors’ arrival.
The Cambrian ‘explosion’ took place just a few tens of millions of years after the formation of Earth’s inner core – in relative terms, just a few heartbeats in the planetary clock – and saw the first appearance of major animal groups in the fossil record.
“This research really highlights the need to have something like a growing inner core that sustains a magnetic field over the entire lifetime—many billions of years—of a planet,” says Tarduno.
Matthew Agius is a science writer for Cosmos Magazine.
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