Source: The Guardian

Astronomers have discovered intriguing evidence that an asteroid break-up blanketed Earth with dust millions of years ago. The event dramatically cooled the planet and triggered an ice age that was followed by major increases in numbers of new animal species.

The work, led by Birger Schmitz of Lund University in Sweden, was recently published in Science Advances and provides new insight into the impact of interplanetary events on our planet’s evolution. “We know about the 10km asteroid that crashed on Earth 67 million years ago and killed off the dinosaurs, but this event was very different,” Schmitz told the Observer. “It occurred about 470 million years ago when an asteroid 3,000 times bigger than the dinosaurs-killer was destroyed during a collision with another asteroid beyond the orbit of Mars. It filled the solar system with dust and caused a major dimming of sunlight falling on Earth.”

Reduced radiation caused Earth to cool significantly, setting off a succession of ice ages. Water froze, ice caps spread and sea levels dropped, creating isolated shallow seas that were ideal for generating new species. Cold water also holds more dissolved oxygen, which would also have boosted speciation. Scientists already knew ice ages appeared at this time and that life went through a spectacular increase in biodiversity, particularly in the sea. The first coral reefs began to grow then, and strange tentacled predators called nautiloids appeared. This is known as the great Ordovician biodiversification event, or Gobe.

Scientists have argued over the cause of Gobe, but now Schmitz, after studying dust particles in seabed sediments laid down at this time, says it was triggered by clouds of asteroid dust. “The sediments laid down at this time are rich in the isotope helium-3 – which they could only have picked up travelling through space,” he said. “It is a crucial clue.”

Other scientists have backed his idea. “It isn’t necessarily the answer to every question we have about Gobe, but it certainly ties together a lot of observations,” Rebecca Freeman, of the University of Kentucky, Lexington, told the journal Science recently.

However, Schmitz’s research has also caused interest for another reason. As the world warms dangerously, some scientists have proposed spreading a veil of dust that would sit in space above the Earth and reflect sunlight away from our overheating planet. The idea is controversial because it could have many unpleasant side-effects, say critics.

Now evidence shows such an experiment occurred naturally 470 million years ago. The result was a major change in our meteorology and the evolution of life here. “It is certainly worth bearing in my mind in coming years,” added Schmitz.