Roughly 66 million years ago, an asteroid some 6-9 miles in diameter slammed into the Yucatan peninsula. Researchers have a fairly good idea what happened next. The impact delivered roughly the same force as 10 billion A-bombs (each equivalent to what we dropped on Hiroshima), and would have punched a hole into the Earth some 100 km (62 miles) wide and 30km (19 miles) deep. Kilometers of solid rock were vaporized in an instant. Tsunamis and fires swept the land, drowning and burning huge swathes of the entire planet.
This event is known as the Cretaceous–Paleogene extinction event. The reason we first theorized its existence is thanks to a layer of iridium-rich deposits found all over the planet at the same geologic moment in time. In the aftermath of the Chicxulub impact, some 75 percent of life on Earth died. We have a pretty good idea what happened in the immediate aftermath of the event — after the flames, global temperatures plunged, as soot and sulfur greatly reduced the amount of sunlight reaching the Earth’s surface. But these conditions would have begun to right themselves in a few years as the level of particulates in the atmosphere dropped.
What would have happened after? Climatologists haven’t been sure. The theory has been that after a relatively short-lived temperature drop, temperatures soared again thanks to the huge increase in atmospheric carbon brought on by both the vaporized miles of rock and the enormous burning that circled the globe. But it’s been difficult to find precise fossil record that could speak to the situation (unsurprisingly, the era immediately following the death of much of the life on Earth tends to be chaotic).
The Chicxulub anomaly. The white line is the modern coastline. The degraded crater ring is clearly visible.
New research from Ken Macleod at the University of Missouri suggests that global temperatures did indeed spike immediately following this period. Sixty-six million years ago, parts of Tunisia were covered in warm, shallow seas. And best of all, the fossil beds found at El Kef are full of fish fossils that show evidence of a 5C rise in temperatures following the impact that lasted for 100,000 years. As the temperature rises, the ratio of oxygen-16 isotopes to oxygen-18 isotopes within the fish fossils changes, because the amount of each isotope present in the original environment had changed. Shifts in these isotope ratios is one way we measure whether the climate was warming or cooling across time.
The research team examined roughly 350,000 years of history across the 9-meter long core sample, and discovered the sharp deviation on top of a bed of clay. The clay layer represents the chaotic and turbulent impact itself. The isotope ratios above and below it are sharply different, representing the conditions that existed before and after the impactor struck.
One of the interesting aspects to this study that backs up work we’ve seen done overall is the idea that surges of this sort take time to return to baseline conditions, even if the initial source is removed. The wave of destruction caused by the Chicxulub impact event would’ve happened in a manner of minutes to hours, but it took the climate a hundred thousand years to return to baseline. There are also implications for how long it could take humans on Earth to reverse the impact of our own climate shifts.
“The atmosphere was loaded for a very brief interval of time, and the consequences of that change in atmospheric composition lasted for 100,000 years,” MacLeod told NPR. “So it illustrates, I think, really strongly, even if we went back to 1850 levels of carbon dioxide emission, it’s going to take a 100,000 years for the carbon dioxide that we’ve already put in the atmosphere to cycle through the Earth’s systems.”