Palaeothermometer: Determining the temperature of the Chicxulub Crater left by asteroid that killed the Dinosaurs

A novel technique made it possible to establish the temperature inside the Chicxulub crater shortly after the asteroid impact that ended 75% of life on Earth about 66 million years ago.

Crater asteroid
The asteroid that fell on Earth about 66 million years ago ended with 75% of the life on the planet. The crater that left such an impact is located north of the Yucatan Peninsula, in Mexico.

A group of researchers has determined using a "palaeothermometer" the temperature of the Chicxulub crater just after the asteroid that killed the dinosaurs created it 66 million years ago. They relived the history of that moment that completely changed the planet. According to a study published on January 11 in the journal PNAS Nexus, the rocks sampled inside the crater reached about 330 ºC at the end of the Cretaceous period, between 145 and 66 million years ago.

The impact crater is located north of the Yucatan peninsula, near the Chicxulub population, to which it owes its name. It was found in the late 1970s while oil deposits were being searched in the area, but it was associated with this catastrophic event for the planet several years later.

The new research also suggests that the impact of the asteroid did not release as much carbon dioxide as was thought, which could change the way scientists consider the mass extinction event that followed, as referred to by Live Science. The Chicxulub crater was formed when a space rock 12 kilometres wide and traveling at about 43,000 km/h crashed into the Earth, creating a bowl about 200 kilometres wide in what is now the Gulf of Mexico.

The violent waves of the tsunami helped fill most of the crater with sediment in the minutes and hours after the impact, and then it was buried under layers of rock deposited in the millions of years since the impact. The main author of the study, Pim Kaskes, a geologist at the Free University of Brussels, explained that "it is not so easy to access it, but, on the other hand, it is very well preserved. You just have to find the right rocks, the appropriate material, and apply the right techniques to unravel their mysteries."

The chemistry of the paleothermometer

The team of researchers studied samples taken in 2016 in the region of the peak ring of the centre of the crater. They applied a thermometry of grouped carbonate isotopes, or "palaeothermometer" to the rocks. This method reconstructs old temperatures by detecting the abundance of heavy isotopic bonds of carbon-13 and oxygen-18 in carbonate minerals.

The temperature initially generated by the impact of the asteroid would have been between thousands and tens of thousands of degrees Celsius, but Kaskes pointed out that they could not measure it because those rocks were probably vaporised. However, they were able to look for the temperatures recorded in the rocks right after the initial impact. These observations have important climatic implications for the Cretaceous-Paleogene mass extinction event, since current numerical models probably overestimate the release of carbon dioxide (CO2) from the Chicxulub impact event.

The value obtained of 333 °C, came from rocks collected more than 700 meters below the ocean floor. After the impact of the asteroid, these rocks were much warmer than the maximum temperature of the late Cretaceous ocean of about 35.5 °C and what researchers would expect from the burial and the known hydrothermal activity below the crater, in the range of 50 to 200 °C, suggesting that something else was happening. "If you have temperatures above that range and the isotopic values are outside the known hydrothermal values, it is most likely that there is another process involved," Kaskes said.

Less CO2 was released than previously thought

The second process involved may have been a thermal decarbonation and a rapid reverse reaction, in which the highly reactive calcium oxide is recombined with the carbon dioxide released from the vaporised rock, forming new calcium carbonate crystals, according to Kaskes and his team. If that is the case, then less carbon dioxide entered the atmosphere than previously thought after the impact of the asteroid because a large amount was quickly reused to produce calcium carbonate.

crater structure
Location of the Chicxulub crater and vertical cut of its structure. Image: PNAS Nexus.

This evidence leads us to think that less carbon dioxide in the atmosphere could have reduced global warming and the acidification of the oceans during the subsequent mass extinction that killed 75% of all species, including non-avian dinosaurs, although researchers are still debating how the climate changed at the end of the Cretaceous, as reported by Live Science.

The "palaeothermometer" used in the new research sheds light on the events that occurred 66 million years ago. It can also be applied to other impact craters around the world, which opens up opportunities to learn more about the impacts of asteroids. Knowing in detail how these processes work is crucial so that the history of our planet and the history of our species can be understood. But it is also evidence that we are much more vulnerable to the forces of the universe than we believe.