Earth’s Solid Inner Core Makes Life On Planet Possible
Life on Earth became possible when the planet’s solid inner core emerged hundreds of millions of years ago, according to new research.
Scientists say that around 565 million years ago, the Earth’s magnetic field strength fell to 10 percent of its strength today.
It then suddenly bounced back just before the emergence of animals in what scientists call the Cambrian explosion or “biological big bang.”
The team say this rejuvenation happened at the same time as Earth’s inner core was formed, and was likely caused by it.
This magnetic field is vital to life on Earth because it shields the planet from radiation emitted by the sun.
It is generated in our planet’s outer core by swirling liquid iron around 1,800 miles below our feet.
The swirling liquid iron causes electric currents, driving a phenomenon called the geodynamo that produces the magnetic field.
The researchers say the rejuvenation meant Earth avoided the fate of Mars, which once had a magnetic field before it disappeared.
The red-hot planet is vulnerable to the sun’s radiation and has no oceans.
While Earth may not have been guaranteed to meet the same fate had its magnetic field not re-emerged, it would have lost far more water and be far drier than it is today.
The American team say the rejuvenation happened over a few tens of millions of years, which is in fact quick on geological timescales.
In their research paper, the academics worked out key dates in the inner core’s history, including a more precise estimate of how old it is.
Earth is made of layers: the crust, where life is found; the mantle, Earth’s thickest layer; the molten outer core and the solid inner core, which is, in turn, composed of an outermost inner core and an innermost inner core.
For decades, scientists have been trying to understand how Earth’s magnetic field and core have changed throughout our planet’s history.
They cannot directly measure the magnetic field because it is so hot and so far below the Earth’s surface.
Minerals that rise to Earth’s surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field at the time they cool from their molten state.
For the study, the team used a carbon-dioxide laser and a hi-tech magnetometer to analyze crystals from the rock anorthosite.
These have tiny magnetic needles that are “perfect” for recording magnetism.
By studying magnetism locked in ancient crystals, the team worked out two important dates in the formation of the history of the inner core.
They say the magnetic field began to renew itself 550 million years ago, 15 million years after it had collapsed.
The team say the rapid reformation was caused by the formation of a solid inner core, which recharged the outer core and restored the magnetic field’s strength.
The scientists say 100 million years later the growing inner core’s structure changed and the boundary between the innermost and outermost inner core became clear.
These changes coincide with changes around the same time in the structure of the overlying mantle, due to plate tectonics on the surface.
Study author Professor John Tarduno from the University of Rochester in New York said: “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.
“Earth certainly would’ve lost much more water if Earth’s magnetic field had not been regenerated.
“The planet would be much drier and very different than the planet today.”
The findings were published in the journal Nature Communications.
Produced in association with SWNS.