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Smith in STRIDE

An occasional Gate series focusing on the work of STRIDE Scholars.

STRIDE Scholar Gets a Piece of the Rock

By Jennifer DeBerardinis ’11

Katie Castagno ’12 calls it “the rock,” a shiny black chunk of sediment she displayed recently in her geology research lab.

Formed around 720 million years ago, it offers much more than aesthetic appeal. It’s full of what geologists call “roll-up structures”: light, thin lines folded on top of each other throughout the fist-sized sediment sample, an extremely rare geologic configuration.

It may not seem like much to the non-geologist, but these unusual folding structures can provide valuable insight to a time period called Snowball Earth, when the entire globe is believed to have been entombed in ice, said Sara Pruss, assistant professor of geology. 

The small rock is so important, in fact, that Pruss and Castagno, who is working alongside Pruss as a STRIDE (Student Research in Departments) program scholar, are devoting at least a year to its study. 

STRIDE scholarships are paid research assistantships with Smith professors in a variety of disciplines. The two-year scholarships are offered each year to promising first-year students to provide valuable experience in academic discovery. In the past two years, the program has matched 96 students with professors in more than 30 academic areas.

As a STRIDE Scholar, Castagno’s job this semester involves constructing a three-dimensional model of her rare rock “to get a full picture of the roll-up structures,” she explained. Pruss collected the sample a couple years ago from the Republic of Namibia, a country in coastal southwestern Africa. A post-doctoral fellow in geo-biology at Harvard University at the time, Pruss had in mind the rock’s future potential for use in an undergraduate research project.  

This fall, in a fulfillment of Pruss’ planning, Castagno spends her afternoons grinding down the rock a few millimeters at a time in 20 separate steps, snapping photos at each stopping point. Castagno will need the pictures to create a three-dimensional model of the rock before the end of the semester.

Ultimately, she and Pruss are trying to figure out how the structures formed, Castagno said, and that will allow for better understanding of the time period that produced them.

The grinding process, which takes about 15 minutes each step, can be tedious, Castagno said as she showed off the spinning rock grinder. And the procedure involves some trial and error. Since the rock has to be flat, she’s had to carefully trim off the edges a few times.

But the payoff is enormous, she added. Not only is she learning about how the earth looked millions of years ago. She is also gaining hands-on experience in the lab.  “You can see the results,” she said.

Next semester, the project will move to chemical analyses of the rock, said Pruss, more specifically dissolving the sediment and looking for organic material.

Pruss believes that microbial mats—large communities of tiny single-celled organisms—were responsible for forming the “roll-up” structures. Seven hundred and twenty million years ago the microbes and sediment existed as a doughy substance, resembling something like Play-doh, she said.

Since fold-up structures are rare—formed just before and after the Snowball Earth period—they provide valuable information about “how the climate was changing and how sediments were being formed,” Pruss said.

Though she doesn’t yet know what exactly caused the roll-up formation—perhaps earthquakes that made microbial mats shake or sloped sediment deposition—she hopes to find the answer as part of Castagno’s project.

Discovering more about the roll-up structures also allows for a better understanding of the remarkable time period when they were formed, during which the global climate transitioned from one like present-day Greenland more to that of the Bahamas within a few thousand years, Pruss said.

Despite the rock’s ancient formation, the roll-up structure project is vital to current climate studies, said Pruss. “We are in this midst of climate change, and this gives us a better perspective on what’s going on right now.” Information from past climactic changes can be used to determine how the oceans may respond to current global climate change, she said.

Her research, said Castagno, will “definitely help figure out what exactly is going on.”
Castagno, a self-described “non-science person,” said her STRIDE research has turned her on to a field she originally hadn’t considered. Also enrolled in the department’s Geology in the Field course, she’s realized just how much she enjoys the study of sediments.

Castagno will continue grinding the rock until she has enough images to send off for three-dimensional model construction. The project could go on for a while, Pruss said. “These formed once in geologic history . . .there’s so much to understand.”