At the center of the Earth, there was a giant solid iron ball that was slowly swelling up. This is the inner core, and scientists have recently found compelling evidence that its birth half a billion years ago may have played a major role in the evolution of life on Earth.
At that point, our planet’s magnetic field wobbles — and this could have catastrophic consequences, they say. These fields normally protect life on the surface by fending off cosmic radiation and charged particles emitted by our sun.
But 550 million years ago, it slumped to a fraction of its current strength – before suddenly regaining its strength. And after the planet was brought back to life, Earth experienced a sudden proliferation of complex multicellular life on its surface. This was the Cambrian explosion, when most of the major animal groups first appeared in the fossil record. Scientists have now linked it to events at the center of the Earth.
Our planet consists of spheres. There is a layer of rock 5-70 km thick that covers the ground like an egg shell. This is called the crust and underneath is a 3,000 km long silicate mantle. At the bottom is the outer core, which is made of molten iron, and inside is another sphere – of solid iron. It is more than 2,000 kilometers in diameter and grows about one millimeter per year.
“Earth’s magnetic field is generated by the eddies of iron 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 liquid and its ability to generate magnetic fields collapsed.”
Analysis of crystals in rocks in Quebec by Tarduno’s team shows that Earth’s magnetic field is less than 10% of its current strength and would provide poor protection against cosmic and solar radiation. It is said that the dynamo driving the Earth’s magnetic field probably lost strength due to the rapid loss of heat from the core.
Then the core begins to harden in the middle, which has serious consequences. This is essentially a turbocharging motion in the outer core, returning a force to the planet’s magnetic field. “Our research shows that the formation of the inner core began about 550 million years ago, and that it occurred before the Cambrian explosion,” said Tarduno.
Why and how the inner core is born has been a mystery. From its humble beginnings half a billion years ago, it had grown into a solid iron ball the size of the moon. It is the most mineralized place on Earth and has a major influence on conditions on the surface.
More importantly, it gives our world a magnetic field. Observations of another world – where this field has disappeared – reveal the tragic consequences of this loss. An example is Mars, which lost its magnetic field four billion years ago. Shielded from the solar wind – a constant stream of protons and electrons pouring out of the Sun’s surface – Mars’ atmosphere has been propelled into space, leaving its surface dead and waterless.
“Earth will not grow like Mars, but it will definitely lose more water than it does now if it does not restart its magnetic field,” added Tarduno. “It’s of course a drier planet than we live on today.”
However, geophysicists are reluctant to speculate about how the rise of Earth’s magnetic field may have influenced the evolution of life. “I don’t think that the return of Earth’s magnetic field and the subsequent explosion of life on Earth could be so unrelated. But we can not say what the exact pattern of the incident. This needs further study.”
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