The decline of the dinosaurs, the rise of mammals and, ultimately, the origins of humans were even more unlikely than previously thought, according to new research. The huge asteroid collision that sparked this change in the Earth’s diversity was already a highly improbable roll of the celestial dice. But a new study suggests the mass extinction that followed it was only so severe because of where the asteroid struck.
Scientists believe the dinosaurs were largely wiped out 66m years ago when an asteroid collision released a huge dust and soot cloud that triggered global climate change. The researchers, from Tohoku University in Japan, claim that the soot necessary for such a global catastrophe could only have come from a direct impact on rocks especially rich in hydrocarbons.
Rocks like this would only have been found on about 13% of the Earth’s surface. Add to this the need for a liberal dose of toxic sulphurous compounds in the rocks, and the odds that an impact of the same size (an already astronomically rare event) would have such devastating consequences lengthen to just one in 100.
The impact crater created by the 10km-diameter asteroid is located close to Chicxulub on Mexico’s Yucatán peninsula, and was only identified as recently as 1991. Before then, it was hidden to scientists because it lay partly under a blanket of sediment on the seabed.
The underlying rocks were composed of gypsum (rich in sulphur) and also contained large reserves of hydrocarbons. Had the impact occurred a few hundred miles away, or indeed at most locations on the globe, then the consequences of the collision may have been vastly less severe. Terrestrial dinosaurs and many other groups may never have been driven to extinction, and their survival may have hindered or completely prevented the later spread of mammals – and, of course, humans.