Asteroid dust helps solve the mystery of dinosaur extinction


Over 99% of all organisms that have ever lived on Earth are now extinct. Most of them died quietly. However, in Earth’s history there have been five major mass extinction events – known as the Big Five – in which many species have gone extinct at the same time.

Each of the five great events caused at least a 40% loss of all species on Earth. Yet humans hold a particular grudge against the most recent, which brought the 160-million-year-old dinosaur story to a sudden end. It was the Cretaceous-Paleogene extinction, and it happened 66 million years ago, wiping out about 75% of all species on Earth at the time. With the exception of sea turtles and crocodiles, no four-legged animal over 25 kg survived.

After decades of heated debate, scientists have decided on two main theories about the causes of this extinction. The first possibility is the impact of an asteroid that created the 180 km-wide Chicxulub impact crater in Mexico’s Yucatán Peninsula. Second, a series of eruptions in a volcanic area known as the Deccan Traps in India.

Last week, an international team of scientists with data from four independent laboratories published a study claiming to have ended the debate. They say the 12 km-wide asteroid is to blame.

A closed case?

The study examined rock samples collected from the crater, which is now underwater. They found a layer of earth mud mixed with “space dust” containing the element iridium, which can be found in high concentrations in meteorites but which is rare in the earth’s crust. This layer was four times thicker in the impact crater than in the surrounding area.

The team found a 5cm layer of sediment immediately below the limestone of the Early Paleogene, the geological period that began immediately after the extinction. This thin layer of sediment exhibited iridium concentrations of one part per billion, compared to 0.04 part per billion in the earth’s crust.

A map showing the location of the Chicxulub crater, in the Yucatán Peninsula.