First day of dinosaur extinction recorded in rocks at asteroid impact site

Researchers probing the impact that wiped out the dinosaurs find evidence of wildfires and tsunami in the rocks at ground zero.

An international team led by University of Texas and including Imperial College London researchers analysed more than 130 metres of rock that had built up over just one day - the day after the asteroid struck.

At least 325 billion metric tons of sulphur would have been released by the impact. That’s about 10,000 times more than the amount of sulphur released during the 1883 eruption of Krakatoa Professor Joanna Morgan

By analysing the rocks, they found evidence that a resurging ocean and tsunami swept material back into the crater formed by the asteroid. They also found charcoal from wildfires, which along with soot, sulphur and dust blasted into the atmosphere, blocked the sun and caused global cooling.

This scenario has long been suggested by scientists investigating why the dinosaurs, and 75 per cent of all life on Earth, were wiped out by the asteroid - but this is the first direct evidence from the crater itself.

The team’s results are published today in Proceedings of the National Academy of Sciences .

At ground zero

Professor Sean Gulick , from the University of Texas Institute for Geophysics (UTIG), who led the latest study said: “It’s an expanded record of events that we were able to recover from within ground zero. It tells us about impact processes from an eyewitness location.”

Most of the material that filled the crater within hours of the strike was produced at the impact site, offshore of the Yucatan Peninsula in Mexico, or was swept in by seawater pouring back into the crater from the surrounding Gulf of Mexico.

In just one day, nearly 130 metres of material built up inside the crater — a rate that’s among the highest ever encountered in the geologic record. This rate of accumulation means that the rocks recorded what was happening in the environment within and around the crater in the minutes and hours after impact, and can also give us clues about the longer-lasting effects of the impact.

Researchers estimate the asteroid hit with the equivalent power of 10 billion atomic bombs of the size used in World War II. The impact event ignited trees and plants that were thousands of miles away and triggered a massive tsunami that reached as far inland as Illinois, 2000 km away.

Cooling climate

Inside the crater, researchers found charcoal and a chemical marker associated with soil fungi that shows signs of being deposited by resurging waters. This suggests that the charred landscape arrived at the crater at the same time as the receding waters of the tsunami.

Professor Joanna Morgan , from the Department of Earth Science and Engineering at Imperial, who co-led the project to drill into the crater and co-authored the new study, said: “At least 325 billion metric tons of sulphur would have been released by the impact.

"That’s about 10,000 times more than the amount of sulphur released during the 1883 eruption of Krakatoa, which cooled the Earth’s climate by an average of 1.2°C for five years.”

Although the asteroid impact created mass destruction at the regional level, it was the change in global climate that caused a mass extinction, killing off the dinosaurs along with most other life on the planet at the time.

‘ The First Day of the Cenozoic ’ by Sean P. S. Gulick et al. is published in Proceedings of the National Academy of Sciences. Photos and graphics subject to third party copyright used with permission or Imperial College London.

Hayley Dunning
Communications and Public Affairs