By Colin BarrasJan. 20, 2020 , 3:00 PM Earth’s earliest lands, hot and hellish, were sheltered from above. Researchers have found more evidence that our planet had a strong magnetic field 4.2 billion years ago, three-quarters of a billion years earlier than previously thought and just 350 million years after the Earth formed. The field would have shielded Earth, protecting its atmosphere from being stripped away by high-energy particles from the sun—and perhaps helping life gain a foothold. With few surviving rocks to study, geologists struggle to reconstruct the time known as the Hadean, which ran from 4.55 billion years ago to 4 billion years ago. But fragmentary—and controversial—clues can be found in younger, 3-billion-year-old rocks from the Jack Hills of Western Australia. These rocks contain tiny crystals of a hardy mineral called zircon, which are chips off an even older block: 4.2-billion-year-old Hadean rocks that formed from cooling magma. The crystals also preserve evidence of an ancient magnetic field, according to an international team led by John Tarduno, a geophysicist at the University of Rochester, New York. Not all researchers are convinced by the result, because it would push back the accepted birth date of Earth’s magnetic field by… Read full this story
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