Sun-blocking dust from asteroid impact drove the dinosaur extinction

When a huge asteroid hit Earth 66 million years ago, clouds of dust from pulverised rocks blocked out the sun for 15 years. This dust may have been the primary driver of the mass extinction that saw off the non-avian dinosaurs and many other species, according to new research.

The Chicxulub impactor ejected plumes of sulphur-based gases into the atmosphere alongside vast amounts of silicate dust. The impact also triggered wildfires around the planet, which emitted soot and carbon dioxide into the air.

Soon after, the world fell into an “impact winter”, which wiped out 75 per cent of species on the planet.

“The research on this proposes the Chicxulub mass extinction was mainly governed by either sulphuric gas emissions or soot injections from global wildfires,” says Cem Berk Senel at the Royal Observatory of Belgium in Brussels.

However, previous research hasn’t considered whether the silicate dust could have had an effect too, he says.

To investigate further, Senel and his colleagues analysed fine-grained material deposited at a site in North Dakota at the time of the Chicxulub impact. The team found that the diameter of the grains ranged from 0.8 to 80 micrometres, with an average size of 2.88 micrometres.

Putting this information into a climate model, the team found that sulphur gases were the primary driver of global cooling initially, by blocking sunlight. However, these gases only stuck around in the atmosphere for about eight years.

Meanwhile, silicate dust lingered in the air for 15 years after the impact, which suggests that it must have played a large role in sustaining the global winter. The researchers found that the dust alone contributed to a 15°C drop in Earth’s surface temperature, and this effect gradually weakened after the first couple of years.

The dust was also more effective than the sulphur gases at blocking the wavelengths of light used for photosynthesis in plants and phytoplankton.

“Only the silica dust resulted in long-lasting photosynthetic shutdown after impact,” says Senel. This led to a lack of food for many species, setting off a series of extinctions on land and in the oceans.

Senel and his colleagues now hope to study the climatic effects of the asteroid impact on a much longer timescale. “There’s still so many big questions to uncover about what happened to life after one of the biggest mass extinction events,” he says.