Scientists have found dust from the asteroid that wiped out the dinosaurs inside the crater it left.
Earth has experienced five major mass extinction events - known as the big five - during which many species became extinct at the same time. Yet humans hold a particular grudge against the most recent one, which brought a sudden end to the 160-million-year history of the dinosaurs. This was the Cretaceous-Paleogene extinction and it happened 66 million years ago, wiping out about 75% of all species on Earth at the time. Except sea turtles and crocodiles, no four-legged animals bigger than 25kg survived.
After decades of heated debate, scientists settled on two leading theories about what caused this extinction. The first possibility is the impact of an asteroid which created the 180km wide Chicxulub impact crater in the modern day Yucatán Peninsula in Mexico. Second, a series of eruptions in a volcanic area known as Deccan Traps in India.
Now, finally, an international team of scientists with data from four independent laboratories has published a study claiming to have ended the debate. They say the 12km-wide asteroid was the one to blame.
The study looked at rock samples collected in the crater, which is now under water. They found a layer of terrestrial mud mixed with “space dust” containing the element iridium, which can be found in high concentrations in meteorites but is rare in the Earth’s crust. This layer was four times thicker in the impact crater than in the surrounding area.
Spikes of iridium in dust from this time have been found in over 100 places around the world from America, Asia, Europe, Oceania, all the way to Antarctica. These were first identified in findings from the 1980s, however they did not win a global consensus because the evidence couldn’t link the high iridium concentrations to the Chicxulub crater. But this new study provides this crucial link.