A giant asteroid is credited for killing off the dinosaurs, but it wasn’t the rock alone – the cascading effects of the impact destroyed Earth’s livability for millennia. Now scientists have identified a new factor, in fine silicate dust that hung in the atmosphere for well over a decade, blocking sunlight and drastically cooling the planet.
About 66 million years ago, an asteroid at least 10 km (6.2 miles) wide slammed into Earth and released the energy equivalent to about 4.7 billion times that of the bomb dropped on Hiroshima. Needless to say, that’s a pretty bad day for any living thing anywhere near that spot, with the fossil record showing a mass grave some 3,000 km (1,865 miles) away where fish were launched from the water by shockwaves and buried by mud, debris and burning hot bullets of glass raining down from the molten rock in the sky.
This burning rain also sparked huge wildfires, while tsunamis up to a mile high circled the world’s oceans, and mega-quakes rumbled for months afterwards. Sulfuric acid would have rained down, making oceans too acidic for life. And material gathering in the atmosphere would have blocked out sunlight for well over a year, cooling the planet drastically, killing off photosynthesizing plants and triggering the collapse of food webs. It’s no wonder that around three quarters of all life on Earth was wiped out.
In the new study, scientists have identified an overlooked factor in that most devastating of doomsdays.
Previously, it was thought that the impact winter – a period of extreme cold – that followed was mostly due to vaporized sulfur from the impact itself, and from soot emitted by the widespread wildfires. Most other scientists ignore the contributions of silicate dust, also ejected from the ground, but this study found that might not be wise.
The researchers examined the minerals preserved in rock at a fossil site in North Dakota, USA – the same one with all the unlucky fish. To their surprise, they found that there were far more fine particles of silicate dust than expected.
When they punched in the concentration of dust they found, as well as the size distributions of the particles, into a climate model, they found that these tiny fragments could have hung in the atmosphere for up to 15 years after the impact, cooling the Earth’s surface by as much as 15 °C (27 °F). That’s a huge climate shift, considering the projected impacts we’re currently facing as a result of 2 °C (3.6 °F) of warming.
Every new piece of information adds to our understanding of just how bad an impact of this size was for the planet, and highlights the importance of keeping a vigilant watch on the skies in future.
The research was published in the journal Nature.