Mbad extinctions are not fun times. There is a reason (usually more than one, actually) species that disappear en mbade. That makes unraveling these reasons a challenge. The investigation of the geological crime scene is difficult since the clues can be difficult to reach after millions of years, and the events are complex.
The extinction that annihilated (most of) the dinosaurs, for example, had a great impact on asteroids and lived volcanic eruptions that covered most of what is now India in lava flows. Although the impact would have darkened the sky, bringing with it a permanent winter for several years, the injection of greenhouse gases into the atmosphere by volcanoes would have produced a rapid change in the direction of warming when the sky cleared.
The record of that however, the warming in the geological record is not very good. The problem has been finding an adequate climate record in the rocks that were deposited fast enough to show relatively short periods of time in detail. To get that kind of record, a team led by Kenneth MacLeod of the University of Missouri scraped rocks in Tunisia in search of pieces of crushed fossil fish.
The researchers mark both boxes – a good climatic record and many details – resorting to Tunisian rocks with fish bones. The rocks that date from the time of the mbad extinction of the Late Cretaceous have been well studied, with the ages and characteristics of several layers nailed quite accurately. At the time of the extinction event 66 million years ago, the sediments in these rocks were being deposited in a shallow ocean in the tropics. Many fossils of creatures made of calcium carbonate were altered over time, making them unreliable sources of information. But these fish parts are made of more resistant calcium phosphate.
It is the oxygen atom in that calcium phosphate that keeps the secrets, as it does in the H 2 O of the glacial ice or the calcium carbonate of other bugs The oxygen ratio more Heavy -18 to lighter isotopes of oxygen-16 change with temperature. Then, when descending through an ice core or through a layer of rock, changes in this ratio of isotopes indicate heating or cooling.
In this case, the researchers made measurements on 9 meters of rock, covering about 350,000 years of Earth history. At 40 points in time, they collected dozens of small pieces of fish fossils to badyze the oxygen isotopes. The results show a change in the impact moment of the Chicxulub asteroid that lasted 100,000 years.
The oxygen isotope ratio was displaced by an amount representing water that was approximately 5 ° C warmer than it had been. After about 100,000 years of that, the temperatures are more or less where they were before the impact, although the samples are a bit scarce here to say more than that.
It is expected that the tropical ocean heats less than the world average, so it represents more than 5 ° C of global warming. (By comparison, unrestricted greenhouse gas emissions could cause global warming caused by humans at about 5 ° C by the year 2100). This is aligned with some estimates of the expected warming. A 2002 study that estimated the change in CO 2 from plant fossils, for example, put average global warming at the 7.5 ° C stage. The most interesting thing here is to see how it lasted that warmer climate: 100,000 years also fits with the simulations of climate models of this era. Then, while the world changed in the blink of an eye, misery took a while to go.
All estimates of the drivers of short-term cooling and long-term warming still have fairly large error bars. It is data like this that helps reduce some of that uncertainty: a small piece of fish fossil crushed at once.
Science 2018. DOI: 10.1126 / science.aap8525 (About DOIs).