In choosing where to pursue a doctoral degree, Betsey Pettitt said she looked for a “graduate school program that would challenge me and make me step out of my comfort zone.” Pettitt, a native of Ashland, New Hampshire, found just that at Rensselaer Polytechnic Institute.
She worked with two professors and simultaneously developed two sets of skills in their different lab environments. Not only did she earn her doctorate in geology, she developed a new instrument that is making ground-breaking measurements of ancient atmospheric gases trapped in rocks and minerals.
“I’ve always been intrigued by earth sciences,” Pettitt said. “Why am I driving over mountains right now? Why is this river here? Why do the waves crash the way they do? That’s what drew me to geology.”
Pettitt came to Rensselaer with a bachelor’s degree in geology from the University of New Hampshire and undergraduate research experience that earned her access to the low-temperature geochemistry lab of Morgan Schaller, an assistant professor of earth and environmental sciences, and the high-temperature geochemistry lab of Bruce Watson, an Institute Professor of earth and environmental sciences. The concept she devised with these co-advisers marries technology from one lab to answer questions in another.
“I was tasked with the idea of trying to develop and design an instrument that would be able to measure gas in different geological materials to ultimately try to reconstruct past atmospheric compositions,” Pettitt said.
Working with Watson, an expert in solid-Earth geochemistry, Pettitt studied methods for calculating the rates at which gases diffuse in various geological materials in order to understand the retentiveness of the material. With that understanding, she worked with Schaller to measure the atmospheric gases in materials found at the surface of the Earth, like soil carbonate nodules found in both modern and ancient soils and sedimentary quartz-bearing rocks, that were formed millions of years ago. Locations where ancient soils and microcrystalline quartz-bearing rocks were formed and persist at the surface to the present day can date back hundreds of millions — and even billions — of years old.
“Right now, we’re going back to the Triassic, which is about 215 million years ago, but our hope is to use this method to determine levels of atmospheric gases as far back as the Archean period, which ranges from 2.5 to 4 billion years ago,” Pettitt said.
To do so, Pettitt developed a custom instrument that includes a crushing device, where the samples are introduced, then attached to a high-vacuum system to achieve very low pressures and subsequently crushed to release the trapped gases. The resulting gases are measured using a quadrupole mass spectrometer. She corrects the unknowns and uses a calibration curve to determine the amount of gas released from a particular sample.
“What makes this system so powerful and unusual is that we’re measuring extremely small quantities of the atmospheric gases, from pico- to femto-moles. That hasn’t been rigorously done in the past,” Pettitt said.
Having completed her degree, Pettitt is considering job opportunities, with particular interest in a position at a national laboratory.