Privileged Planet: magnetic field history II (Introduction)

by David Turell , Thursday, February 21, 2019, 21:36 (2102 days ago) @ David Turell

Other new commentary about the severe loss of our magnetic field about 565 million years ago:

https://www.scientificamerican.com/article/ancient-earths-weakened-magnetic-field-may-h...

"Some 565 million years ago, life on Earth dodged a bullet. The magnetosphere—the magnetic field that surrounds our planet like a protective shield—had degraded to its lowest intensity ever, according to a study published January 28 in Nature Geoscience. Stripped of this shielding, Earth could have been blasted by atmosphere-eroding outbursts from the sun, gradually losing most of its air and water until it became as dry and desolate as present-day Mars.

"Instead, deep in the planet’s interior an event was taking place that would help the magnetosphere rebound, according to the study’s authors. Earth’s liquid-iron inner core crystallized, a process geophysicists call “nucleation.” Once solid, the rotating core acted as a whirling dynamo, strengthening the protective electromagnetic bubble that wrapped around Earth, staving off planet-wide devastation. That, in turn, could have set the stage for the Cambrian explosion, an event approximately 541 million years ago in which the biosphere suddenly experienced the greatest evolutionary expansion in the planet’s history.

"The weakened magnetic field Tarduno and his colleagues discovered roughly coincided with the end-Ediacaran extinction around 542 million years ago—a mass die-off of primitive, sessile, sea-dwelling organisms that preceded the Cambrian explosion. In 2016 Carlo Doglioni, a geologist at Sapienza University of Rome, proposed the Cambrian’s profusion of new life-forms took place in part because of the magnetosphere’s growing strength. “The magnetic dipole was increasing after the Ediacaran,” Doglioni says. “We have a good, thick atmosphere that is protecting us from ionizing radiation because we have a good, strong magnetic field.” Fossil evidence suggests the organisms that endured the end-Ediacaran extinction survived by burrowing into the seafloor—a trait not shared by the immobile Ediacaran period biota that died out. As for the actual culprits in the killings, a 2016 study from Joseph Meert, a geologist at the University of Florida, blames harmful ultraviolet light and cosmic radiation that bathed the surface after passing through ancient Earth’s weakened magnetic field and thinning atmosphere. “When the shields went down, the Ediacaran organisms went extinct, clearing the ecological space for the later Cambrian explosion,” he says."

Comment: Same warning as usual. Although the Cambrian Explosion appeared, there is no evidence of what drove it.