The anthropogenic influence on the Earth’s climate today is profoundly intimidating – but long before these mankind-induced problems existed, the earth was forced to content with similar experiences on a number of occasions.
Researchers at Northwestern University investigating the condition of the earth at the time of the asteroid impact that brought a wretched end to the reign of the dinosaurs 66 million years ago confirmed that the earth was doomed to imminent destruction due to unruly surge of carbon levels in the oceans.
By examining the calcium isotope composition of fossilized clam and snail shells from the Cretaceous-Paleogene mass extinction event, they found that – leading up to the extinction event – soaring carbon dioxide (CO2) levels greatly affected the shells’ chemistry.
This influx of carbon dioxide in the atmosphere was likely due to sustained eruptions from the Deccan Traps – one of the largest volcanic provinces stretching an area of roughly 200,000 square miles – located in modern India. Immense amount of carbon dioxide (CO2) expelled from the province completely engulfed the atmosphere, and what followed was acidification of the oceans, making the lives there uninhabitable.
Put simply, the Earth was already unstable and under stress even before asteroid Chicxulub strike.
“Our data suggest that the environment was changing before the asteroid impact,” explained Benjamin Linzmeier, the lead author of the study and a postdoctoral researcher at the Institute for Sustainability and Energy at Northwestern, in a news release. “Those changes appear to correlate with the eruption of the Deccan Traps.”
“The Earth was clearly under stress before the major mass extinction event,” said Andrew D. Jacobson of Northwestern’s Weinberg College of Arts and Sciences. “The asteroid impact coincides with pre-existing carbon cycle instability. But that doesn’t mean we have answers to what actually caused the extinction.”
Earlier investigations to establish the correlation between the Deccan Traps eruptions and the mass extinction event couldn’t really get a clear picture of what really led to extinction as it was based on examining bulk sediments and use of chemical tracers. But this time, the team drew on seashells and gained a more comprehensive understanding on chemical composition of the ocean.
The reason the team centered their attention towards the shells is that its main composition is calcium carbonate, the same compound you find in chalks, limestone and marvel. Carbon dioxide present in the water dissolves it, but in the process of formation of the shells, it affects only the shell composition rather than breaking them down. And, because they grow quickly and live for such a short period of time, they provide a snapshot of the ocean’s chemistry during a particular point in time.
For the study, the team turned to shells found in the Lopez de Bertodano Formation, a region on the west side of Seymour Island in Antarctica known for its rich collections of well-preserved fossils of flora, dinosaurs and birds. Analyzing the shell’s calcium isotope compositions, they found that shells’ chemistry already shifted following the spate in the levels of carbon in the oceans long before the Chicxulub asteroid struck the planet.
To examine the shells’ calcium isotope composition, researchers used a cutting-edge technique developed in Jacobson’s laboratory at Northwestern. Apparently, it requires shell samples to be dissolved in order to segregate calcium from other elements, then running a mass spectrometry experiment.
“We can measure calcium isotope variations with high precision,” Jacobson said. “And those isotope variations are like fingerprints to help us understand what happened.”
“We expected to see some changes in the shells’ composition, but we were surprised by how quickly the changes occurred,” Linzmeier said. “We also were surprised that we didn’t see more change associated with the extinction horizon itself.”
Understanding how the Earth responded to previous bouts of climate change and how it managed to recuperate from CO2 inundation, researchers say, can help us stay prepared for how the planet will respond to the present, mankind-inflicted climate crisis.
“To some degree, we think that ancient ocean acidification events are good analogs for what’s happening now with anthropogenic CO2 emissions,” Jacobson said. “Perhaps we can use this work as a tool to better predict what might happen in the future. We can’t ignore the rock record. The Earth system is sensitive to large and rapid additions of CO2. Current emissions will have environmental consequences.”
The study will be published in the January 2020 issue of the journal Geology.