New computer analysis suggests that it was volcanism, not an asteroid that may have caused the demise of the dinosaurs.

For decades, scientists have engaged in a vigorous debate over whether the demise of the dinosaurs 66 million years ago could be attributed to an asteroid strike or massive volcanic eruptions. This catastrophic event marked the termination of the Cretaceous Period, resulting in the extinction of approximately three-quarters of all life on Earth, including nonbird dinosaurs.

In a ground-breaking approach, researchers have introduced a novel methodology to determine the true perpetrator responsible for the dinosaurs' demise: employing computers to analyse the evidence.

According to the team's findings published in Science on September 29, the computational analysis indicates that the extinction event was primarily triggered by massive emissions of gas generated by the Deccan Traps volcanic eruptions. Spanning a duration of around one million years, these eruptions released vast quantities of gas-laden lava, enveloping what is now western India.

"Instead of approaching it with a perspective of assigning blame to volcanoes or asteroids and attempting to explain the reasons behind their actions, our objective was to minimize human influence and bias in the process," states Alexander Cox, a computational geologist from Dartmouth.

The aim was to retrace our steps by utilizing evidence obtained from the crime scene. Scientists possess persuasive evidence: cores extracted from deep-ocean sediments contain geological data that indicate the release of hazardous gases into the atmosphere, specifically carbon dioxide, which contributes to global warming, and sulphur dioxide, which leads to ocean acidification.

However, Cox suggests that these gases could have originated from either the asteroid impact, which would have incinerated rocks on the Earth's surface, or the eruptions at the Deccan Traps.

Previous attempts to ascertain the origin of the gases have predominantly concentrated on timing, specifically investigating the occurrences of lava emplacement during the Deccan Traps eruptions, as indicated by Cox (SN: 2/21/19). However, our knowledge regarding the quantity of initial gas contained within the lava remains purely speculative. According to Cox, estimated levels of carbon dioxide concentrations in the lava have exhibited a considerable degree of variation, differing by a factor of ten. Consequently, our approach to this matter has been cantered on a gas-emissions standpoint, an alternative to the conventional lava-flow perspective.

To disentangle the relative contributions of each potential culprit, Cox and Dartmouth geologist C. Brenham Keller utilized a statistical model known as a Markov chain Monte Carlo approach. This meticulous approach systematically evaluates the likelihood of various scenarios pertaining to gas emissions from different sources. As the simulation outputs gradually converge with geologic observations, possible solutions come into focus.

The researchers' method gained significant strength through the utilization of 128 distinct processors that operated concurrently, as highlighted by Cox. "At the end of each model run, all the processors compared their performance, akin to classmates comparing answers." Through this parallel computing strategy, computations that would have originally required a year were completed within only a few days.

The data utilized by Cox and Keller in their study constituted observations derived from three deep-sea sediment cores, each spanning a period approximately 67 to 65 million years in the past. Within these sediments, foraminifera, microorganisms inhabiting the ocean, possessed carbonate shells containing diverse isotopes of carbon and oxygen. The composition of these shells serves as an archival record of past oceanic chemistry and enables inferences regarding historical global temperatures, marine biodiversity, and carbon exchange between the atmosphere, ocean, and land (SN: 1/16/20).

The computer simulations determined that the quantity of gas emitted into the atmosphere solely from the volcanic activity was sufficient to explain the observed variations in temperature and carbon cycling as indicated by the data obtained from the drill cores of foraminifera.

According to the analysis conducted, it is unlikely that the asteroid strike, which resulted in the formation of the extensive Chicxulub crater in present-day Mexico, caused a significant surge in carbon dioxide or sulphur dioxide levels (SN: 1/25/17).

Many scientists remain unconvinced that these findings offer the definitive answer to this enduring and intricate question. According to Sierra Petersen, a geochemist at the University of Michigan in Ann Arbour, this approach represents an elegant means of tackling the problem. By employing this modeling technique, it becomes possible to ascertain the consensus solution by considering multiple proxy records. However, Petersen acknowledges that the output of the model is contingent upon the input, as is the case with any model.

Petersen also points out that foraminifera shells are not an ideal proxy for ancient temperatures. Changes in the oxygen isotope ratios within these shells can be attributed not only to temperature variations but also to alterations in seawater composition. As a result, different temperature proxies would likely yield differing patterns of gas release when replicated in models, notes Petersen.

Regarding the suspected culprit behind the mass extinction event, Petersen expresses her scepticism about the study's conclusion that the impact was not responsible for the extinction. Although she agrees that the study indicates the impact likely did not result in a significant release of gas, she believes it is too much of a leap to completely discount the impact's role. According to Petersen, the asteroid may still have had other detrimental consequences on the planet's environment.

Furthermore, Clay Tabor, a paleo climatologist from the University of Connecticut in Storrs, emphasizes that the Chicxulub impact triggered numerous catastrophic effects that extend beyond the scope of the carbon dioxide and sulphur dioxide emissions explored in this study. Tabor highlights the formation of vast clouds of soot and dust, resulting from the pulverization of rocks caused by the impact. Previous research has suggested that this dust may have significantly reduced the amount of sunlight reaching the Earth, potentially inducing a frigid winter that swiftly eliminated plant life and destroyed habitats (SN: 7/17/20).

Moreover, the recent study indicates that the asteroid collision had no lasting impact on the planet's carbon cycle, as determined by the carbon isotope data gathered from foraminifera shells spanning one million years after the extinction event. Nonetheless, Tabor asserts that there was a sudden decline in the abundance of these organisms corresponding to the time of impact. He suggests that the rapid and drastic changes caused by the Chicxulub impact likely played a significant role in its effects on life.

Tabor explains, "Numerous geochemical records spanning the extinction event, in addition to this modelling research, fail to adequately capture the rate of changes associated with the Chicxulub impact. While the impact may have released considerably less CO2 and SO2 than the Deccan Traps, it did so almost instantly." Thus, even if the asteroid impact emitted fewer gases overall, Tabor reaffirms that the speed of their release could have been tremendously catastrophic nonetheless.