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A giant asteroid dust cloud may have sparked new life on Earth 470 million years ago

Creatures of the seafloor in the late OrdovicianAstronomers in Sweden have discovered new evidence that an exploding asteroid blanketed Earth's atmosphere with dust about 470 millions of years ago, causing the planet to cool dramatically. The ice ages that followed led to a rapid increase in the number of new animal species, a stage in the evolution of life on Earth which scientists call the Great Ordovician Biodiversification Event (or GOBE).



Asteroid destroyed following a collisionAccording to the team led by Birger Schmitz of Lund University, Sweden, the asteroid measured 150 kilometres (nearly 100 miles) across. That's 3000 times bigger than the one that crashed to Earth 66 million years ago, wiping out the dinosaurs and many other species. The asteroid was destroyed during a collision with another asteroid beyond the orbit of Mars. Vast clouds of dust from the collision would have swirled around the inner Solar System. About 1000 times the current levels of dust gathered in Earth's atmosphere, causing a major dimming of sunlight falling on Earth. This caused the planet to cool significantly, setting off a series of ice ages. As water froze and became "locked up" in the expanding ice caps, sea levels dropped.


Fossilized brachiopods in late Ordovician rock
Shallow seawater—particularly cold water, which contains more dissolved oxygen—is an ideal environment for nurturing new species. This explains, at least in part, the spectacular increase in biodiversity (range of living things) during the Ordovician Period that scientists have already identified from the fossil record. At the time, the living world (which was confined to the oceans; there was no life on land) was dominated by marine invertebrates, with a type of cephalopod probably the top predator. During the GOBE, a large number of brachiopods, gastropods and bivalves evolved. Coral reefs also first appeared at this time.


Creatures of the seafloor in the late OrdovicianSchmitz and his team studied the geological evidence: tiny fossilized meteorites contained in limestone rock layers dating from the Ordovician Period. The meteorites' chemical composition revealed they were fragments from an asteroid that must broken up at the time the sediments—which later formed the limestone—were laid down. “The sediments ... are rich in the isotope helium-3 (a variant of the element helium) which they could only have picked up travelling through space,” said Schmitz. “It is a crucial clue.”
Photo acknowledgements (from the top): James St. John, NASA, Wilson44691, James St. John

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