Ka-boom!: New research argues that ancient diversity rose phoenix-like from the flames of numerous asteroid impacts 470 million years ago.

Credit: NASA/Don Davis

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NEW YORK: Asteroids, oft maligned as harbingers of doom, might have sparked one of the greatest explosions of biodiversity in Earth's history.

A new theory suggests that an intense period of asteroid impacts 470 million years ago led to a "renaissance" of diversity on Earth, during the so-called Great Ordovician Biodiversification Event (GOBE).

Biological renaissance

For more than a decade, Birger Schmitz, a geologist at the University of Lund in Sweden, and colleagues have steadily gathered evidence of widespread asteroid impacts in rocks from that age. In a new study detailed in a recent issue of the journal Nature Geoscience, the team show that the impacts occur just before a spike in biodiversity, when the number of creatures in Earth's seas tripled or quadrupled.

Life before the asteroids was "primitive," Schmitz said, consisting mainly of invertebrates including worms and snails. Many of these species survived the bombardment, but sharing life's stage with them were new organisms, many more complex and specialised than anything that came before.

"One can say that the [GOBE] represents the time when biodiversity changed from an all-time low to modern levels," Schmitz said. It's unclear how the asteroids and the biodiversity spike are linked, but one possibility is that the impacts created new environmental niches for life on Earth, forcing organisms to change and adapt.

It's also possible that – in an event similar to the one that foreshadowed the rise of mammals after the demise of the dinosaurs – the asteroid impacts might have wiped out the most dominant forms of animal life at that time, giving other types a chance to flourish.

Give and take

But why would asteroid impacts have helped spawn new life in one instance, but wiped out the dinosaurs in another?

Schmitz thinks that the invertebrates that dominated early Earth might have been hardier than the more sophisticated, but also more sensitive, creatures that appeared later. "The primitive low-diversity fauna of the lower Ordovician was used to rough conditions, and may have reacted entirely differently to impacts than the highly evolved, complex ecosystems of the late Cretaceous," he said.

Florentin Paris, a geologist at the University of Rennes in France, believes the correlation between the GOBE spike and the impacts is unlikely to be a coincidence, but said that more work is required before the hypothesis is likely to be widely accepted.

"If additional work supports the provocative and interesting hypothesis suggested by Schmitz and co-authors, it will no longer be appropriate to regard projectiles from space solely as 'killers,'" Paris commented in a related Nature Geoscience commentary.