When the dinosaurs were wiped off the face of the planet, how did they leave? Was it a slow, plodding decline or a short sharp bang? Back in the 1960s and 1970s, debate about this question was mainly taking place on the ground, at fossil sites in places like Montana. Paleontologist Robert Sloan and his colleagues documented evidence for the long-term decline of dinosaurs over a 10m to 20m-year period. Dinosaurs had been losing out, ever so slowly, to the rising mammals, mainly as a result of cooling climates.
The asteroid thought to have killed the dinosaurs smashed into the Earth with a billion times more energy than the atomic bombs dropped on Hiroshima and Nagasaki. Many believe the impact caused a mass extinction, wiping out the dinosaurs on land and numerous lifeforms in the oceans. But one of the difficulties in knowing exactly whether and how this happened is that the Chicxulub crater left by the asteroid is buried below a thick layer of sedimentary rock.
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.