Greater than 99% of all organisms which have ever lived on Earth are actually extinct. Most of those simply died out quietly. Nonetheless, in Earth’s historical past there have been 5 main mass extinction occasions – referred to as the large 5 – throughout which many species turned extinct on the identical time.

Every of the large 5 occasions induced at the very least a 40% lack of all species on Earth. But people maintain a specific grudge towards the latest one, which introduced a sudden finish to the 160-million-year historical past of the dinosaurs. This was the Cretaceous-Paleogene extinction, and it occurred 66 million years in the past, wiping out about 75% of all species on Earth on the time. Apart from sea turtles and crocodiles, no four-legged animals greater than 25kg survived.

After many years of heated debate, scientists have settled on two main theories about what induced this extinction. The primary risk is the affect of an asteroid that created the 180km large Chicxulub affect crater within the modern-day Yucatán Peninsula in Mexico. Second, a collection of eruptions in a volcanic space referred to as Deccan Traps in India.

Final week, a world crew of scientists with knowledge from 4 impartial laboratories revealed a research claiming to have ended the controversy. They are saying the 12km-wide asteroid was the one accountable.

A case closed?

The research checked out rock samples collected within the crater, which is now underwater. They discovered a layer of terrestrial mud combined with “house mud” containing the ingredient iridium, which might be present in excessive concentrations in meteorites however is uncommon within the Earth’s crust. This layer was 4 instances thicker within the affect crater than within the surrounding space.

The crew discovered a 5cm layer of sediment instantly beneath the limestone from the earliest Paleogene, the geologic interval that started instantly after the extinction. This skinny layer of sediment had iridium concentrations of 1 half per billion, in comparison with the 0.04 components per billion within the Earth’s crust.

A map showing where the Chicxulub crater is, in the Yucatán Peninsula.