At the center of the Earth, there is a giant ball of solid iron slowly swelling. This is the inner core, and scientists have recently uncovered intriguing evidence that its birth half a billion years ago may have played a major role in the evolution of life on Earth.
At that time, our planet’s magnetic field was faltering – and this could have had disastrous consequences, they say. This field typically protects life on the surface by fending off cosmic radiation and charged particles emitted by our sun.
But 550 million years ago, it plummeted to a fraction of its current strength – before suddenly regaining its strength. And in the wake of this planetary reboot, Earth experienced a sudden proliferation of complex, multicellular life on its surface. This was the Cambrian explosion, when most major animal groups first appeared in the fossil record. Scientists have now linked it to events located at the center of the Earth.
Our planet consists of spheres. There is a rocky layer 5-70 km thick that covers the ground like eggshell. This is called the crust and below it is the mantle of 3,000 km of silicate. To the bottom is the outer core, which is made of molten iron, and inside is another ball – of solid iron. It has a diameter of more than 2,000 kilometers and grows by about a millimeter per year.
“Earth’s magnetic field is generated by iron vortices in the outer core,” said John Tarduno, professor of geophysics at the University of Rochester in New York. “Before the Cambrian explosion, the core was completely molten and its ability to generate a magnetic field was collapsing.”
Analysis of crystals in rocks in Quebec by Tarduno’s team showed that Earth’s magnetic field was less than 10% of its current strength and would have provided poor protection against cosmic and solar radiation. It is said that the dynamo driving the Earth’s magnetic field was likely losing strength due to rapid heat loss from the core.
Then the core began to solidify in its center, which had serious consequences. It’s basically the motions of a turbocharging in the outer core, returning the force to the planet’s magnetic field. “Our research indicates that the formation of the inner core began about 550 million years ago, and that it occurred before the Cambrian explosion,” Tarduno said.
Why and how the inner core was born has been a mystery. From its small beginning half a billion years ago, it has grown into a moon-sized ball of solid iron. It is the most mineralized place on Earth and has a great influence on conditions on the surface.
More importantly, it provided our world with a magnetic field. Observations of other worlds – where these fields have disappeared – reveal the tragic consequences of this loss. An example is Mars, which lost its magnetic field four billion years ago. Unprotected from the solar wind – the constant stream of protons and electrons pouring out of the Sun’s surface – Mars’ atmosphere has been pushed out into space, leaving its surface dead and without water.
“Earth would not have evolved like Mars, but it would certainly have lost more water than it does today if it had not restarted its magnetic field,” Tarduno added. “It was certainly a drier planet than the one we live in today.”
However, the geophysicist was reluctant to speculate exactly how the rebirth of the Earth’s magnetic field would affect the evolution of life. “I do not think that the return of the Earth’s magnetic field and the subsequent explosion of life on Earth can be unrelated. But we cannot say what the exact pattern of events is yet. This needs further study.”
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