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Published in Macalester Today
Cosmochemistry students unravel the mysteries of the solar system from behind a scanning electron microscope in Olin-Rice. “Most geology focuses on the evolution of the earth,” says geology professor Karl Wirth, who taught this new class. “This course extends that inquiry to the origin and evolution of the solar system.”
In developing the course, Wirth asked the Smithsonian Museum of Natural History if he could borrow samples of some of their 35,000 meteorites. From their list he chose a variety of meteorites, which students studied and identified over the course of the semester.
Rather than chunks of rock, the meteorites arrived as slices on slides, roughly one inch in diameter. In the first weeks students learned about the formation of the elements and their abundances in the solar system. Then came the major project: Each student received a meteorite to study and, in groups of two, the 18 students began their investigations.
The class drew students from chemistry, physics and astronomy, and economics as well as from geology. According to Wirth, a collaborative approach is not only more effective for learning, it’s more similar to the ways in which modern scientists actually work.
“I was drawn to this class because I wanted to learn the chronology of our solar system—what formed when and how do we know these ages? I find it fascinating how much information can be extracted from a small rock that landed on the Earth’s surface,” says Clara Thomann ’13 (Corvallis, Ore.), who majored in geology and physics/astronomy.
“I was drawn to this class because I wanted to learn the chronology of our solar system—what formed when and how do we know these ages? I find it fascinating how much information can be extracted from a small rock that landed on the Earth’s surface.”
Using an optical microscope with up to 400x magnification, students imaged the meteorites and identified regions for further investigation. By employing polarized light to differentiate the minerals by color, the students ended up with samples resembling stained glass windows. In the Keck lab—a well-equipped Macalester facility open to students and faculty in all the sciences—students used a scanning electron microscope to produce maps of the mineral compositions, with the amount of a given element—say, aluminum—reflected in the height of its graphed peak. The electron beam that scans the meteorite surface produced x-rays that enabled students to identify the elements present in the specimen.
A portion of meteorite that is only 1 mm x1 mm can be seen as a 10x10-inch image. Wirth spent hours with each student team, familiarizing them with equipment and helping them interpret results.
In designing this course allowing students hands-on experience with Cosmochemistry concepts and techniques, Wirth was inspired by his graduate work with noted astronomer Carl Sagan, says geology major James Lindgren ’15 (Marshalltown, Iowa), who adds, “Cosmochemistry is a unique and wonderful course that I wish everyone could take.”