University of Southern California People At USC

View All
Catherine Powers
Catherine Powers

Catherine Powers

Doctoral Student in Earth Sciences
USC College of Letters, Arts and Sciences

USC doctoral candidate Catherine Powers is conducting research that not only challenges our view of ancient mass extinctions, but also may help scientists predict the effects of climate change on marine life today.

Powers has traveled to fossil sites around the world to analyze the distribution and diversity of bryozoans, a group of marine invertebrates that live in colonies. In the process, she has uncovered evidence that these tiny organisms may have served as a grim bellwether of the greatest mass extinction in Earth’s history.

Some 10 million years before the Great Dying – which saw the disappearance of 90 percent of marine creatures and 70 percent of terrestrial species at the end of the Permian era, about 250 million years ago – bryozoans in the deep ocean began to disappear. They were followed by those on ocean shelves and reefs, and finally those living near shore.

According to Powers’ data, these organisms were the victims of creeping environmental stress. In a deadly sequence of events, massive volcanic eruptions released carbon dioxide and methane into the atmosphere, triggering rapid global warming. As the warmer seawater lost some of its ability to retain oxygen, water rich in hydrogen sulfide – a gas emanating from anaerobic bacteria at the ocean’s floor – welled up from the deep. It was this that killed the bryozoans.

In turn, if large amounts of hydrogen sulfide escaped into the atmosphere, the gas would have killed many forms of terrestrial life. It also would have damaged the ozone shield, increasing the level of harmful ultraviolet radiation reaching the planet’s surface.

What’s more, Powers and her adviser, David Bottjer, a professor of earth sciences at USC College, believe that this same gradual process repeated itself for another major extinction 200 million years ago, at the end of the Triassic era.

Powers and Bottjer reported their findings in the journal Geology in November 2007.