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Featured Scientists

Jennifer McElwain, Ph.D.
Geology Department
Curator, Fossil Plants

Fossil plants allow paleobotanist Jennifer McElwain to reconstruct the Earth’s past climate—from 400 million years ago to the present. By studying the shape and size of a fossilized leaf, she can determine the average temperature and precipitation of the atmosphere in which it grew. By looking at the number of stomata, or tiny pores, on its surface, she can determine the concentration of carbon dioxide (CO2) in the atmosphere at the time.

Utilizing the more than 80,000 fossil plants in The Field Museum’s collections, McElwain is looking at how levels of atmospheric CO2 have changed over time—and how these atmospheric changes have affected Earth’s biodiversity.

In the summer of 2002, she led a National Geographic Society-funded expedition to Greenland, where she and colleagues collected 200-million-year-old plant fossils. The fossils date back to a geological time period known as the Triassic-Jurassic boundary, when 95 percent of all plant species and 70 percent of coral reefs went extinct.

The researchers have already shown that rapid increases in CO2 contributed to this mass extinction when global temperatures rose by 42 to 44 degrees Fahrenheit higher than the present. Carbon dioxide is a greenhouse gas that many scientists believe plays an important role in climate change.

“The whole subject of climate change is very contentious,” says McElwain. “We know we’re burning fossil fuels and, in doing so, Earth is heating up. What we are uncertain about, however, is the role atmospheric CO2 plays in large-scale climate and biotic change. By looking back in time at the relationships between CO2, climate, and biodiversity, we can gain a greater understanding of their interactions and use this information to make better predictions of possible climatic and biodiversity responses in a future higher CO2 world.”

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