Study: Biodiversity of Ordovician radiation unrelated to asteroid breakup

By Brooks Hays  |  Feb. 3, 2017 at 2:31 PM
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Feb. 3 (UPI) -- New research undermines the supposed correlation between an ancient asteroid collision and an uptick in biodiversity on Earth.

Roughly 470 million years ago, Earth experienced a rise in biodiversity known as the Ordovician radiation -- named for the geologic period during which it occurred. Around the same time, Earth was peppered with a barrage of meteorites.

Scientists have suggested the arrival of meteorites -- triggered by the collisions of two large asteroids somewhere between the orbits of Mars and Jupiter -- delivered some life-promoting properties.

It's true that Ordovician strata share both meteorite fossils and evidence of increasing biodiversity. But until now, scientists haven't been able to precisely date the arrival of the meteor cascade.

Enter zircons, the ideal time-telling mineral. Researchers were able to recover zircons from Ordovician rock layers containing fossil meteorites. Because uranium trapped in zircon at the time of its crystallization decays into lead at a stable rate, researchers can analyze its composition and learn the exact time of its deposition in Earth's crust.

Geologists from Lund University sent the zircons to scientists at the Natural History Museum of Denmark for analysis.

"We measure the amount of uranium and lead present in the zircons and from that it is possible to calculate an age that pinpoints the time when they erupted on the surface," researcher Mafalda Costa said in a news release. "In this case, on the same surface that also contained meteorites originating from the asteroid break-up. In this way, we could precisely define the age of the fossil meteorites."

Their findings -- detailed in the journal Nature Communications -- suggest meteors began raining down on Earth some 2.5 million years after the Ordovician radiation began.

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