We are all aware of the fact that climate change and global warming are issues highly related to human activity. But new evidence shows that similar kinds of activities happened long before humans existed.
The study is led by Northwestern University and the researchers investigated the state of the Earth during the times when dinosaurs disappeared because of an asteroid. They found that the condition of Earth was already unstable due to the increase of carbon in the oceans.
This study is the first to measure the calcium isotope composition of fossilized clam and snail shells. The researchers found out that the shell's chemistry changed because of a surge of carbon in the oceans.
This increase in carbon was probably caused by long-term eruptions from the Deccan Traps, which is one of the largest volcanic features on Earth. Before the asteroid impact, the Deccan Traps spewed a huge amount of carbon dioxide into the atmosphere.
The study's first author Benjamin Linzmeier said, "Our data suggests that the environment was changing before the asteroid impact. Those changes appear to correlate with the eruption of the Deccan Traps."
Andrew D. Jacobson, a senior author of the paper, said, "The Earth was clearly under stress before the major mass extinction event. The asteroid impact coincides with pre-existing carbon cycle instability. But that doesn’t mean we have answers to what actually caused the extinction."
Linzmeier also said, "Shells grow quickly and change with water chemistry. Because they live for such a short period of time, each shell is a short, preserved snapshot of the ocean’s chemistry."
Researchers examined shells collected from the Lopez de Bertodano Formation which is a fossil-rich area in the Seymour Island in Antarctica; they analyzed the shells' calcium isotope compositions in Jacobson's laboratory at Northwestern.
Dr. Linzmeier said, "We expected to see some changes in the shells’ composition, but we were surprised by how quickly the changes occurred. We also were surprised that we didn’t see more change associated with the extinction horizon itself."