Privileged Planet: important inner core (Introduction)

by David Turell , Friday, April 01, 2022, 15:31 (754 days ago) @ David Turell

The iron core current movements make the vital magnetic field:

https://www.sciencemagazinedigital.org/sciencemagazine/01_april_2022/MobilePagedArticle...

"Earth’s magnetic field, nearly as old as the planet itself, protects life from damaging space radiation. But 565 million years ago, the field was sputtering, dropping to 10% of today’s strength, according to a recent discovery. Then, almost miraculously, over the course of just a few tens of millions of years, it regained its strength—just in time for the sudden profusion of complex multicellular life known as the Cambrian explosion.

"What could have caused the rapid revival? Increasingly, scientists believe it was the birth of Earth’s inner core, a sphere of solid iron that sits within the molten outer core, where churning metal generates the planet’s magnetic field. Once the inner core was born, possibly 4 billion years after the planet itself, its treelike growth—accreting a few millimeters per year at its surface—would have turbocharged motions in the outer core, reviving the faltering magnetic field and renewing the protective shield for life. “The inner core regenerated Earth’s magnetic field at a really interesting time in evolution,” says John Tarduno, a geophysicist at the University of Rochester. “What would have happened if it didn’t form?”

"Just why and how the inner core was born at that moment is one of many lingering puzzles about the Pluto-size orb 5000 kilo meters underfoot. “The inner core is a planet within a planet,” says Hrvoje Tkalčic´, a seismologist at Australian National University (ANU)—with its own topography, its own spin rate, its own structure. “It’s beneath our feet and yet we still don’t understand some big questions,” Tkalčic´ says.

***

"ALL THIS COMPLEXITY appears to be geologically recent. Scientists once placed the inner core’s birth back near the planet’s formation. But a decade ago, researchers found, using diamond anvils at outer core conditions, that iron conducts heat at least twice as fast as previously thought. Cooling drives the growth of the inner core, so the rapid heat loss combined with the inner core’s current size meant it was unlikely to have formed more than 1 billion years ago, and more than likely came even later. “There’s no way around a relatively recent appearance of the inner core,” says Bruce Buffett, a geodynamicist at UC Berkeley.

"Tarduno realized rocks from the time might record the dramatic magnetic field changes expected at the inner core’s birth. Until recently, the paleomagnetic data from 600 million to 1 billion years ago were sparse. So Tarduno went searching for rocks of the right age containing tiny, needle-shaped crystals of the mineral titanomagnetite, which record the magnetic field’s strength at the time of their crystallization. In a 565-million-year-old volcanic formation on the north bank of the St. Lawrence River in Quebec, his team found the crystals—and convincing evidence that the magnetic field of the time was one-tenth the present day strength, they reported in 2019. The fragility of the field at the time has since been confirmed by multiple studies.

"It was probably a sign that rapid heat loss from the outer core was weakening the convective motions that generate the magnetic field, says Peter Driscoll, a geodynamicist at the Carnegie Institution for Science. “The dynamo could have been close to dying,” he says. Its death could have left Earth’s developing life—which mostly lived in the ocean as microbes and protojellyfish—exposed to far more radiation from solar flares. In Earth’s atmosphere, where oxygen levels were rising, the increased radiation could have ionized some of this oxygen, allowing it to escape to space and depleting a valuable resource for life, Tarduno says. “The potential for loss was gaining.”

"Just 30 million years later, the tide had turned in favor of life. Tarduno’s team went to quarries and roadcuts in the Wichita Mountains of Oklahoma and harvested 532-million-year-old volcanic rocks. After analyzing the field strength frozen in the tiny magnetic needles, they found that its intensity had already jumped to 70% of present values, they reported at the AGU meeting. “That kind of nails it now,” Tarduno says. He credits the growth of the inner core for the field jump, which he says is “the true signature of inner core nucleation.”

"Around the same time, life experienced its own revolution: the Cambrian explosion, the rapid diversification of life that gave rise to most animal groups and eventually led to the first land animals, protomillipedes that ventured onto land some 425 million years ago.

"It just may be that the clement world they found owes much to the inner iron planet we’ll never see, 5000 kilometers below."

Comment: our lives and all of previous life depends on that iron core properly producing the protective magnetic field. Why did the sudden potential loss get turned around? Serendipity? Perhaps the designer stepped in. So much required contingency by chance? And note the field strengthened right in time for the Cambrian Explosion. Another lucky coincidence? The one skipped area is all of the supporting research studies, and may not download for use without my subscription.