SBU’s Troy Rasbury: geology and ancient extinctions

Enormous and powerful though they were, dinosaurs didn’t appear on the Earth and muscle out other animals — mostly reptiles. Somehow, many of those reptiles, who were eating, sleeping and reproducing for about 50 million years during the Triassic period, died during a major extinction event, making it possible for dinosaurs to dominate during the Jurassic period.

What, scientists have wondered, caused such a major shift from one set of creatures to another?

In a new paper in the prestigious journal Science, researchers from Stony Brook University, Columbia, MIT, Rutgers and Université Mohammet Premier in Oujda, Morocco believe they may have the answer.

These scientists, including Associate Professor Troy Rasbury from SBU, looked at rocks in Newark, N.J., and Hartford, Conn., that were a part of an area called the Central Atlantic Magmatic Province, which is likely the largest of the Large Igneous Provinces. These rocks suggest that a large outpouring of gases and aerosols may have been responsible for the extinction.

The lava and gases were released in four pulses over 600,000 years, which is a relatively short time frame for such violent environmental changes.

Scientists had known about the extinction and the lava flows, but they hadn’t been able to pinpoint the time frame over which the Earth may have been less habitable. During the Triassic period, the Earth was just starting to break apart from a period when it was the supercontinent called Pangaea.

The researchers used a process called uranium-lead dating using zircon. Zircon crystals that are millions of years old are extremely resistant to lead. They do, however, include uranium. The only way lead, however, can become embedded in the crystals is if it starts out as an isotope of uranium and decays slowly into lead.

This dating technique, coupled with others that examine the periodic effect of other celestial bodies like the planets in our milky way, has greatly enhanced the ability to narrow down the time span during which these major events occurred.

“There’s definitely rocks contemporaneous with extinction,” said Rasbury. “We can imagine that there’s a lot of gases that come with that, as they’re being erupted. There’s an out-gassing and an environmental deterioration. That’s the link.”

Rasbury praised the work of her colleagues, who have done “a tremendous job” by analyzing samples that were collected from the surface.

“That’s what makes this such a special study. The ages are demonstrating that it’s plausible,” she said. The coincident timing of the presence of these gases and the animal turnover suggests there may be a causal link between the mass extinction and the relatively sudden environmental change.

Rasbury’s main role in this study is to bring the team together. She put together the National Science Foundation proposal that provided some of the funding for this research.

Rasbury and her colleagues at Stony Brook will soon be able to do some of the same research on other rock samples. The university received funding for a mass spectrometer. The lab had a grand reopening on April 19.

“The equipment is here and there’s a lot of hard work in front of us to make sure we can do the high-precision analysis,” she said. “It requires an enormous amount of attention to details.”

Born in North Carolina but raised in Texas, Rasbury speaks at a rapid pace.

“I had a professor at the University of New Orleans who said he didn’t know it was possible to have a Texas accent and talk that fast,” she laughed.

Her identical twin Sidney Rasbury Hemming, who was born 27 minutes before Troy, is also a geologist and attends some of the same professional gatherings.

“I was at a meeting and everybody was calling me Sidney because we talk and laugh the same,” she said.

Rasbury is married to Department of Geosciences Professor William Holt. The couple, who live in East Setauket, have two daughters. Rebecca, 12, is in sixth grade at Setauket School while Virginia, who will be 9 next month, is in third grade.

The house is filled with rocks, although Rasbury said her daughters bring many of them in from the beaches. Her daughters also love to go to gem and mineral shows.

She and her husband talk about geology at home “as long as our kids will let us.”