ACT Science

Practice session

Scientist 1 argues that the mass extinction at the Cretaceous-Paleogene boundary (~66 million years ago) was caused primarily by a large asteroid impact. Evidence includes: a global iridium layer at the K-Pg boundary, shocked quartz grains found worldwide, and a large impact crater (Chicxulub) in the Gulf of Mexico. Scientist 2 argues the extinction was caused primarily by massive volcanic eruptions (Deccan Traps, India), which released CO2 and SO2 over hundreds of thousands of years, causing global cooling and acid rain. Which of the following findings would most strongly support Scientist 1's hypothesis?

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