What exactly happens during and immediately after the impact of a meteorite? That was the question posed by a team of geologists from the research group Archaeology, Environmental Changes & Geo-Chemistry (AMGC) at Vrije Universiteit Brussel. The Chicxulub crater in Mexico is best known because of the extinction of the dinosaurs at the end of the Cretaceous period 66 million years ago. However, it is also a natural laboratory for studying the consequences of processes linked to a meteorite impact. Using a new chemical method, the team were able for the first time to carry out temperature measurements deep in a meteorite crater. The first seconds after the violent impact remain elusive because most material simply evaporated, but in the moments after, lumps of limestone, with newly formed calcite minerals, rained down. “These are ideal for applying the new measurement techniques,” says lead author of a new study and geologist Pim Kaskes, who carried out his PhD in 2023. “We used carbonate clumped isotope thermometry, a new technique that allows us to accurately define the temperature at which calcite minerals and fossils are formed.”
Palaeoclimatologists and co-authors Marta Marchegiano and Marion Peral of AMGC explain: “These analyses are normally used to reconstruct water temperatures from ancient sea deposits, with the aim of detecting changes in the climate. Usually, we find temperatures in the range 10-30° Celsius. In this case, we wanted to see if we could test these techniques on meteorite impacts where processes take place related to very high temperatures.”
Kaskes: “We concentrated on carbonate fragments in several drill cores across the entire Chicxulub crater and found elevated temperatures, up to 327° Celsius. The highest temperatures we came across could not be explained simply by the effect of hot liquids in a large hydrothermal system within the crater. When I inspected the samples under the microscope, I found small, cuboid calcite crystals. Due to the intense shock of the meteorite impact, the carbonate rocks emitted CO2, but a large part of the CO2 likely remained inside the crater, where it formed calcite crystals with the highly reactive CaO (quicklime). These crystals look very similar to those from an experimental study in which we used a hot laser to break down carbonates, so that was an interesting analogy for us.”
Previous climate models have therefore overestimated the total CO2 emissions of the impact, because a large amount of the CO2 would have remained in the crater. This insight has implications for understanding of the short- and long-term effects of the Chicxulub impact on the climate and on life on Earth. Despite the lower CO2 emissions, the impact still had catastrophic effects on the end of the Cretaceous period, like those recently demonstrated in a study on fine particulate matter involving Kaskes and VUB professors Philippe Claeys and Steven Goderis, among others.
The new chemical technique has proved to be a versatile paleothermometer capable of addressing diverse scientific questions. Particularly in the field of planetary geology: Kaskes believes this study is only the beginning of unravelling rapid and extreme processes resulting from meteorite impacts. “Our findings open up many new possibilities for future research, because we can now also apply this thermometer to fragments and ejecta from other impact craters around the world, provided there is sufficient well-preserved carbonate material available,” he says.
The findings were published on 11 January 2024 in the Proceedings of the National Academy of Sciences (PNAS) Nexus: https://doi.org/10.1093/pnasnexus/pgad414