The dinosaur extinction 66m years ago was most likely caused by a comet or big asteroid hitting the Earth. But given that asteroids don’t actually hit our planet very often, could this really be the whole story? Many scientists are now asking whether some sort of cosmological event could have boosted the number of comets at the time, making such a collision more likely.
In a recent book, American cosmologist Lisa Randall suggests that a huge disk of “dark matter” – a type of invisible matter that is five times more common than “normal” matter – could have been responsible. When sweeping past our solar system such a disk would cause a tiny perturbation in space, amounting to a flicker in the gravitational force that can knock comets out of the solar system’s Kuiper belt or the Oort cloud just outside and send them towards the Earth.
But how credible is this theory? And are there other cosmological events that could explain the issue?
A tricky question
Mounting astrophysical and cosmological evidence suggests that there is a lot more dark matter in our galaxy than normal matter. Although it is invisible, we know it is there because of the gravitational pull it has on objects surrounding it.
The fact that it is dark simply means that it does not emit or absorb light, which makes it difficult to spot. Most cosmologists believe this matter, which is after all part of our galaxies and galaxy clusters, moves slowly, and is “cold” (because fast-moving particles are hot).