Around 65 million years ago, a massive asteroid crashed into the Gulf of Mexico. Photo / 123rf
The apocalyptic time that many believe wiped out the dinosaurs has been reconstructed by scientists in unprecedented detail.
They found tiny droplets of sulfuric acid formed high up in the air after the well-known impact of a large asteroid 66 million years ago, blocking the sunlight for several years.
They say this 'big chill' had far more catastrophic effects that first though, causing global temperatures to plummet for three years, even mixing oceans and killing off sea life.
"The big chill following the impact of the asteroid that formed the Chicxulub crater in Mexico is a turning point in Earth history,' says Julia Brugger from the Potsdam Institute for Climate Impact Research (PIK), lead author of the study to be published today in the Geophysical Research Letters.
"We can now contribute new insights for understanding the much debated ultimate cause for the demise of the dinosaurs at the end of the Cretaceous era."
Previous theories focused on the shorter-lived dust ejected by the impact.
Previous theories focused on the shorter-lived dust ejected by the impact.
The new computer simulations show that the droplets resulted in long-lasting cooling, a likely contributor to the death of land-living dinosaurs.
"These dramatic environmental changes suggest a pivotal role of the impact in the end-Cretaceous extinction," the team concluded.
Plants died, and death spread through the food web.
An additional kill mechanism might have been a vigorous mixing of the oceans, caused by the surface cooling, severely disturbing marine ecosystems.
To investigate the phenomenon, the scientists used computer simulations normally applied in different contexts, a climate model coupling atmosphere, ocean and sea ice.
It adds to previous research showing that sulfur- bearing gases that evaporated from the violent asteroid impact on our planet's surface were the main factor for blocking the sunlight and cooling down Earth.
In the tropics, annual mean temperature fell from 27 to 5 degrees Celsius.
"It became cold, I mean, really cold," says Brugger.
Global annual mean surface air temperature dropped by at least 26 degrees Celsius. The dinosaurs were used to living in a lush climate.
After the asteroid's impact, the annual average temperature was below freezing point for about 3 years.
Evidently, the ice caps expanded.
Even in the tropics, annual mean temperatures went from 27 degrees to mere 5 degrees.
"The long-term cooling caused by the sulfate aerosols was much more important for the mass extinction than the dust that stays in the atmosphere for only a relatively short time.
"It was also more important than local events like the extreme heat close to the impact, wildfires or tsunamis," says co-author Georg Feulner who leads the research team at PIK.
It took the climate about 30 years to recover, the scientists found.
The study of Earth's past also shows that efforts to study future threats by asteroids have more than just academic interest.
"It is fascinating to see how evolution is partly driven by an accident like an asteroid's impact - mass extinctions show that life on Earth is vulnerable," says Feulner.
"It also illustrates how important the climate is for all lifeforms on our planet. Ironically today, the most immediate threat is not from natural cooling but from human-made global warming."
Researchers studying the resulting Chicxulub crater recently created a stunning animation to show that the object that hit the planet may have slammed nearly all the way through the Earth's crust.
The animation shows how the impact caused the Earth's surface to slosh back and forth like a liquid.
The finding could help explain how impacts can change the faces of planets, and how collisions can create new habitats for life.
Speaking to Live Science, Sean Gulick, a marine geophysicist at the University of Texas at Austin, and co-author of the study, explained that while asteroids do occasionally hit the Earth, changes to the surface are largely the result of rain and wind, as well as "plate tectonics, which generate mountains and ocean trenches."
Other rocky planets in our solar system, such as Mars, differ, as weather and plate tectonics have little effect on the surface.
Mr Gulick said: "The key driver of surface changes on those planets is constantly getting hit by stuff from space."
The researchers, from Imperial College, London and the University of Texas at Austin, hoped to learn more about the impact effects found on other objects in the solar system.
Large craters often have rings of hills, known as 'peak' rings in their centre.
But studying these is difficult, as they mostly exist on extraterrestrial rocky bodies, and are hard to access.
To overcome this issue, the researchers look at the Chicxulub crater, in Mexico, which was the result of a huge asteroid crash, 66 million years ago.
The crater represents the only intact peak ring on Earth, which has not been eroded.
The researchers drilled 1,335 metres (0.8 miles) below the sea floor to examine rock samples at the impact site.
In the samples, they discovered granite, that was likely to have been buried deep for about 500 million years.
Mr Gulick said: "These deeply buried rocks rose up to the surface of the Earth within the first few minutes of the impact.
"They showed evidence they experienced a high degree of shock from the impact."
After the asteroid had hit, the researchers believe that the earth would have behaved like a 'slow-moving fluid.'
Mr Gulick said: "The stony asteroid would have opened up a hole probably almost the thickness of Earth's crust, almost 30 km [18 miles] deep, and on the order of 80 to 100 km [50 to 62 miles] wide."
The Earth would have then begun to flow to fill in the hole, collapsing the sides of the crater inwards, he said.
Mr Gulick said: "At the same time, the centre of this hole starts reaching upwards, like when you throw a rock in a pond and you get a water droplet rising in the middle.
"The centre would have risen up from the surface of the Earth as much as 15 km [9 miles], and then become gravitationally unstable, collapsing downwards and outwards."
The BBC has described the rock lifting as creating 'instant Himalayas', which is around 8,848 m.
This process would have resulted in the peak ring of mountains.
As well as understanding this process, the researchers also discovered that the rocks from the peak rings were more porous and less dense. This would have provided niches for simple organisms to take hold.
At the same time, nutrients would have been provided from water heated inside the Earth's crust.
Professor Joanna Morgan, lead author of the study from Imperial College's Department of Earth Science and Engineering, said the early surface of the earth was mainly solid granite - lacking spaces for life to evolve.
She said: "The impact created rocks that were highly fractured with a ridiculously high porosity. This was basically quite a good thing for early life.
"The little gaps in the rocks provided a habitat for tiny organisms to grow."
She added: "It is hard to believe that the same forces that destroyed the dinosaurs may have also played a part, much earlier on in Earth's history, in providing the first refuges for early life on the planet.
"We are hoping that further analyses of the core samples will provide more insights into how life can exist in these subterranean environments."
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