Veil of dust from ancient asteroid breakup may have cooled Earth.

Pedro_P

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An asteroid collision 466 million years ago created meteorites that still fall to Earth.NASA/JPL-CALTECH
▼ Faced with a dangerously warming world, would-be geoengineers have dreamed up ways to quickly turn down the heat. One proposed technique: spreading a veil of dust that would sit in space or Earth's atmosphere and reflect sunlight. Researchers say they have now found evidence for a similar experiment that played out naturally, 466 million years ago, when an asteroid out in space exploded into bits. Dust from the breakup blanketed the planet, says Birger Schmitz, a geologist at Lund University in Sweden, plunging it into an ice age that was soon followed by an explosion in animal life.
The ancient episode offers both encouragement and caution for geoengineers. If Schmitz is right, it dramatically demonstrates how dust can cool the planet. But the deep freeze is a lesson in potential unintended consequences. "Maybe our study will trigger a big academic controversy," says Schmitz, who leads a study published this week inScience Advances.
All over the world, the ratio of decaying isotopes in a common meteorite type suggests the space rocks formed in a singular shock event 466 million years ago. Models based on how long they took to cool suggest they came from a 150-kilometer-wide parent body, which broke up in a collision in the asteroid belt beyond Mars, sending a stream of fragments into the inner solar system. Bits from the breakup still fall to Earth today.
Schmitz's team has found a rich source of the debris: a limestone quarry in southern Sweden. Since the 1990s, it has yielded more than 100 fossil meteorites, found in rock layers that date to soon after the asteroid breakup. "The flux had to be enormous at this time," says Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, who has studied the breakup.
The meteorites fell about the time early animal life boomed. Major animal groups had already evolved, but during this Great Ordovician Biodiversification Event (GOBE), ocean animals doubled or even tripled in biodiversity. Reefs built by microbes gave way to some of the first coral reefs, trilobites grew larger, and tentacled predators such as nautiloids diversified and swarmed the mostly fishless seas. In 2008, Schmitz argued that the asteroid breakup might be responsible. Perhaps, he and colleagues proposed, large fragments striking Earth spurred the GOBE by shaking up ecosystems, clearing out ecological niches for new species to evolve into.
But the idea didn't catch on, in part because (▪ ▪ ▪)

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chanakyakripa

Quite a fascinating hypothesis. The veil of dust acting as a giant reflector. At same time, one has to keep in mind that the residual heat also will not find an escape route.