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Earth was stressed before dinosaur extinction

Fossilized seashells show signs of global warming, ocean acidification leading up to asteroid impact

  • Shells’ chemistry shifted to respond to influx of carbon into the oceans, corresponding with Deccan Traps eruption
  • Researchers studied clam and snail shells collected from Seymour Island, Antarctica
  • Study is first to examine the shells’ calcium isotope composition across this interval
  • Researcher: ‘Each shell is a short, preserved snapshot of the ocean’s chemistry’

EVANSTON, Ill. — New evidence gleaned from Antarctic seashells confirms that Earth was already unstable before the asteroid impact that wiped out the dinosaurs.

The study, led by researchers at Northwestern University, is the first to measure the calcium isotope composition of fossilized clam and snail shells, which date back to the Cretaceous-Paleogene mass extinction event. The researchers found that — in the run-up to the extinction event — the shells’ chemistry shifted in response to a surge of carbon in the oceans.

This carbon influx was likely due to long-term eruptions from the Deccan Traps, a 200,000-square-mile volcanic province located in modern India. During the years leading up to the asteroid impact, the Deccan Traps spewed massive amounts of carbon dioxide (CO2) into the atmosphere. The concentration of CO2 acidified the oceans, directly affecting the organisms living there.

“Our data suggest that the environment was changing before the asteroid impact,” said Benjamin Linzmeier, the study’s first author. “Those changes appear to correlate with the eruption of the Deccan Traps.” 

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Fossil samples and field work landscape

Please credit all images to Northwestern University

A Northwestern University researcher holds a fossilized clam shell, collected during a field research trip to Seymour Island, Antarctica.
A Northwestern University researcher holds a fossilized clam shell, collected during a field research trip to Seymour Island, Antarctica.
A Northwestern University researcher stands on the Lopez de Bertodano Formation, a well-preserved, fossil-rich area on the west side of Seymour Island in Antarctica.
A Northwestern University researcher stands on the Lopez de Bertodano Formation, a well-preserved, fossil-rich area on the west side of Seymour Island in Antarctica.
A view of the Lopez de Bertodano Formation, a well-preserved, fossil-rich area on the west side of Seymour Island in Antarctica.
A view of the Lopez de Bertodano Formation, a well-preserved, fossil-rich area on the west side of Seymour Island in Antarctica.
Ben Linzmeier stands in the laboratory at Northwestern University.
Ben Linzmeier stands in the laboratory at Northwestern University.
A fossilized snail shell, ready to be analyzed in the laboratory.
A fossilized snail shell, ready to be analyzed in the laboratory.
A fossilized shell is readied for analysis in the laboratory.
A fossilized shell is readied for analysis in the laboratory.
A fossil, collected from Antarctica, in the laboratory at Northwestern University.
A fossil, collected from Antarctica, in the laboratory at Northwestern University.

Interview the Experts

Andrew D. Jacobson

Professor of Earth and Planetary Sciences
Weinberg College of Arts and Sciences

Benjamin Linzmeier

Postdoctoral fellow, University of Wisconsin-Madison
Department of Geoscience