Morocco fossils reveal astounding diversity of marine life just before the asteroid hit Premium
The Hindu
66 million years ago, the Cretaceous period ended. Dinosaurs disappeared, along with around 90% of all species on Earth. Was it a slow, inevitable decline, or did the end come quickly, driven by a disaster?
Sixty-six million years ago, the Cretaceous period ended. Dinosaurs disappeared, along with around 90% of all species on Earth. The patterns and causes of this extinction have been debated since palaeontology began. Was it a slow, inevitable decline, or did the end come quickly, driven by a sudden, unpredictable disaster?
Georges Cuvier, working in the early 19th century, was one of the first palaeontologists. He believed that geological catastrophes, or “revolutions”, drove waves of sudden extinction. In part, his ideas were formed by study of a giant sea lizard, Mosasaurus, that lived and went extinct at the end of the Cretaceous.
Charles Darwin saw the end of the Cretaceous rather differently. He thought extinctions happened gradually, driven by everyday processes working over many millions of years, just as sedimentation and erosion slowly reshaped the land.
The debate continued for over a century, but the idea of catastrophic extinction gained ground as palaeontologists collected more fossil species, timing species’ appearances and disappearances. Massive numbers of species disappeared near the end of the Cretaceous, rapidly, around the world, both on land and in the sea. These severe, rapid, worldwide extinctions implied a severe, worldwide, rapid cause – a catastrophe.
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Finally, in 1980 physicist Luis Alvarez identified a possible driver of the extinctions – a giant asteroid impact, later traced back to an enormous crater beneath the town of Chicxulub, in Mexico. Debris shot into the upper atmosphere by the impact blocked out the sun, causing photosynthesis to stop, and temperatures to plunge.
This didn’t end the debate, however. Some have argued that other events, like volcanic eruption, contributed, or even that the dinosaurs were already on their way out. In these scenarios, the asteroid impact was one of many factors driving the extinctions, or perhaps the final blow to groups in decline.