Privileged Planet: the Earth is in a safe place (Introduction)

by David Turell , Wednesday, August 19, 2020, 23:26 (1348 days ago) @ David Turell

We are on the second spiral arm two-thirds of the way out from the center, but scientists worry a supernova might have caused extinctions in the past. Without evidence so far. But it is an obvious worry:

https://www.sciencedaily.com/releases/2020/08/200818142104.htm

"Imagine reading by the light of an exploded star, brighter than a full moon -- it might be fun to think about, but this scene is the prelude to a disaster when the radiation devastates life as we know it. Killer cosmic rays from nearby supernovae could be the culprit behind at least one mass extinction event, researchers said, and finding certain radioactive isotopes in Earth's rock record could confirm this scenario.

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"A supernova, on the other hand, delivers a one-two punch, the researchers said. The explosion immediately bathes Earth with damaging UV, X-rays and gamma rays. Later, the blast of supernova debris slams into the solar system, subjecting the planet to long-lived irradiation from cosmic rays accelerated by the supernova. The damage to Earth and its ozone layer can last for up to 100,000 years.

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"The team said the key to proving that a supernova occurred would be to find the radioactive isotopes plutonium-244 and samarium-146 in the rocks and fossils deposited at the time of extinction. "Neither of these isotopes occurs naturally on Earth today, and the only way they can get here is via cosmic explosions," said undergraduate student and co-author Zhenghai Liu.

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"Researchers have yet to search for Pu-244 or Sm-146 in rocks from the Devonian-Carboniferous boundary. Fields' team said its study aims to define the patterns of evidence in the geological record that would point to supernova explosions.

"'The overarching message of our study is that life on Earth does not exist in isolation," Fields said. "We are citizens of a larger cosmos, and the cosmos intervenes in our lives -- often imperceptibly, but sometimes ferociously.'" (my bold)

Comment: Perhaps it happened in the past, but no supernova candidates are close enough to us to cause trouble now.