Don’t underestimate the value of a spring break field trip.
For noble gas geochemist Marissa Tremblay, a geology field trip to Death Valley when she was a freshman at Barnard College set her scientific career in motion. While other students slept in the van on the long drives through the desert, she sat up front asking her professor questions, mesmerized by geological time scales.
“Being able to interpret things by looking at the rock record is something that I had never seen or heard of before,” she recalls. “I thought it was really fascinating and I wanted to know more about how you do that.”
Now, 12 years later, Tremblay combines that passion for geology with noble gases – the six inert gases on the far-right side of the periodic table – in her new Thermochronology Lab at Purdue University. Her achievements led to Tremblay being one of four recipients of the 2021 Marion Milligan Mason Awards from AAAS, which recognizes and supports women starting their careers in chemical science research.
“I honestly was surprised I was selected because I do geochemistry, which is not within the conventional realm when you imagine what chemistry is and what chemists do,” Tremblay says.
Specifically, Tremblay works with noble gases, including helium, neon and argon, to reveal secrets of a rock’s past. Secrets like: how long the rock was on the Earth’s surface, roughly when it was at the surface, and how hot it was at the time.
Tremblay began working with noble gases in geochemistry labs as an undergrad. For her Ph.D. work at UC Berkeley, she helped develop a new technique to estimate past climates of the Earth, using cosmogenic noble gases, which form inside rocks and minerals after nuclear reactions with cosmic rays, which are high-energy particles from space. The reactions producing cosmogenic helium and neon only occur on the Earth’s surface or a few meters deep, so the gases are useful for studying erosion rates, landform ages, and past surface temperatures.
The new technique relies on diffusion rates – how fast the gases leak out of the rocks – which is directly caused by temperature. By finding out how much gas remains in the rock, Tremblay can infer how hot it was when the rock lay at the surface.
“We have lots of great ways to look at how past ocean temperatures have changed, but on land we have fewer proxies available to us,” Tremblay says.
Tremblay and her colleagues are using the technique, formally called cosmogenic noble gas paleothermometry, to investigate a variety of paleoclimate questions, including recent glacial retreat and temperature change in the Alps. She also applies more established noble gas methods to study volcanic activity around the time dinosaurs went extinct, and the impact history of the Moon. She hopes to expand even further, looking at past surface temperatures on Mars.
“That’s what I love about what I do – my toolbox enables me to work on many different questions,” Tremblay says.
Once travel to Antarctica is reopened, she will head down to collect rock samples from the McMurdo Dry Valleys near McMurdo Station. The goal is to see if the valleys were indeed colder 3 million years ago, as geologists argue, or if the temperatures were much higher, as climate models suggest.
“We don’t have any ice cores that go that far back in time,” she says. “So, we don’t have records on land in Antarctica that tell us information about how warm it was. I am really excited to apply this technique there.”
The insights could contribute to understanding how ice sheets melted and sea levels rose during the last time the Earth’s atmosphere contained similar levels of carbon dioxide as projected for this century.
She had been scheduled to go this past research season, but of course the COVID-19 pandemic delayed those plans. The pandemic has also slowed getting her lab fully up and running. She had just begun building it out in March 2020 when everyone had to go home. While it’s been challenging to finalize renovations and have equipment installed and calibrated, she’s making progress.
“I am excited for the lab to be functional and for my students to start working with me,” Tremblay says. “I can see it on the horizon.”
In the meantime, she has been enjoying opportunities to build scientific community through social media and through AAAS, especially with the other Marion Milligan Mason Award Winners who come from different chemistry backgrounds. “The more I am interacting with AAAS, the better it is,” she says. “I’m learning a lot, and it’s good to get your science out there.”
She encourages women, regardless of discipline, to not shy away from networking. Tremblay said she was lucky to have two female role models who became her mentors. “Having key mentors willing to support me, be a champion for me, was essential for my success,” she says.
But, she notes, sometimes finding those champions requires outreach.
“Build that network,” she says, “make it as strong as you can, and don’t be afraid to put yourself out there to ask for mentorship.”