PERIODO: 66 MILIONI DI ANNI FA
AREA: DIDATTICA – ESTINZIONI DI MASSA
parole chiave: Dinosauri, estinzione, temperature, oceanografia, climatologia, geologia
Researchers found two warming spikes that coincide with extinction ‘pulses’. A reconstruction of ancient ocean temperatures sixty six million years ago has provided evidence to support the idea one of the planet’s largest mass extinctions was caused by a combination of volcanic eruptions and an asteroid impact. Researchers found two abrupt warming spikes in ocean temperatures that coincide with two previously documented extinction “pulses”, seen near the end of the Cretaceous Period. The first extinction pulse was tied to massive volcanic eruptions in India, the second to the impact of an asteroid or comet on Mexico’s Yucatan Peninsula. This ultimately led to the demise of the majority of dinosaur species. Both events were followed by a warming climate, evidenced by studying the chemical composition of fossil shells using a recently developed technique called the carbonate clumped isotope paleo thermometer.
This technique showed Antarctic ocean temperatures jumped around 14 degrees Fahrenheit during the first of the two warming events, likely the result of massive amounts of heat-trapping carbon dioxide gas released from India’s Deccan Traps volcanic region. The second warming spike was smaller and occurred 150,000 years later, around the time of the Chicxulub impact in the Yucatan.
To create their new temperature record, which spans 3.5 million years at the end of the Cretaceous and the start of the Paleogene Period, the researchers analysed the isotopic composition of 29 remarkably well-preserved shells of clam-like bivalves collected on Antarctica’s Seymour Island. These mollusks lived 65.5-to-69 million years ago in a shallow coastal delta near the northern tip of the Antarctic Peninsula. At the time, the continent was likely covered by coniferous forest, unlike the giant ice sheet that is there today.
As the two-to-five-inch-long bivalves grew, their shells incorporated atoms of the elements oxygen and carbon of slightly different masses, or isotopes, in ratios that reveal the temperature of the surrounding seawater. The isotopic analysis showed seawater temperatures in the Antarctic in the Late Cretaceous averaged about 46 degrees Fahrenheit, punctuated by two abrupt warming spikes.
“This new temperature record provides a direct link between the volcanism and impact events and the extinction pulses – that link being climate change,” said Sierra Petersen, a postdoctoral researcher in the University of Michigan Department of Earth and Environmental Sciences. “We find that the end-Cretaceous mass extinction was caused by a combination of the volcanism and meteorite impact, delivering a theoretical ‘one-two punch”.
The cause of the Cretaceous-Paleogene (KPg) mass extinction, which wiped out the non-avian dinosaurs and roughly three-quarters of the planet’s plant and animal species sixty six million years ago, has been debated for decades. Many scientists believe the extinction was caused by an asteroid impact; some think regional volcanism was to blame, and others suspect it was due to a combination of the two. Recently, there’s been growing support for the so-called press-pulse mechanism. The “press” of gradual changes in climate caused by Deccan Traps volcanism followed by the catastrophic “pulse” of the impact. The new record of ancient Antarctic ocean temperatures provides strong support for this theory, Petersen said. Pre-impact climate warming due to volcanism “may have increased ecosystem stress, making the ecosystem more vulnerable to collapse when the meteorite hit,” he added.
“A previous study found that the end-Cretaceous extinction at this location occurred in two closely timed pulses,” Petersen said. “These two extinction pulses coincide with the two warming spikes we identified in our new temperature record, which each line up with one of the two ‘causal events.‘”
Unlike previous methods, the clumped isotope paleothermometer technique does not rely on assumptions about the isotopic composition of seawater. Those assumptions thwarted previous attempts to link temperature change and ancient extinctions on Seymour Island.
The findings have been previously published in the journal Nature Communications.
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