MARS ROCKS! USING LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS) IN AN INTRODUCTORY GEOLOGY COURSE

We present a novel rock and mineral identification laboratory exercise designed to acquaint introductory geology students with analytical equipment, the scientific literature, and making geologic interpretations from a variety of data. This interdisciplinary exercise utilizes laser-induced breakdown spectroscopy (LIBS), a remote-sensing instrument similar to the one aboard Curiosity, the soon-to-launch Mars Science Laboratory rover. This instrument uses a pulsed neodymium YAG laser which is focused onto a sample surface. A short lived plasma is created, and when it cools it emits wavelengths characteristic of the elemental composition of the sample. A fiber optic spectrometer is used to collect and measure the emitted light, and wavelengths are compared with a database of known values to identify elements.

For this capstone exercise, teams of students investigated the geology of a specific location on the Martian surface. Each team was given location coordinates, a suite of unknown mineral and/or rock samples, and a list of scientific articles on Martian geology and mineralogy. One suite “from” Valles Marinaris contained anhydrite, halite, and basalt. Another suite “from” Eagle Crater contained basalt, magnesium sulfate dust, and hematite. A final suite “from” Olympus Mons contained basalt and zeolite. Students used identification techniques learned earlier in the semester, a mineralogy textbook, and several scientific articles to narrow down the possibilities, then used the “rover” (LIBS instrument) to confirm the sample identification. Undergraduate research students in the Chemistry Department (some of whom wrote the LIBS software) participated in teaching the geology students how LIBS works and helped generate and interpret the resulting spectra. Teams used their results to propose an interpretation for the geologic history of their site location. Students also used satellite and rover images to help with their interpretations.

Each team successfully identified their samples despite not having seen all of the minerals earlier in the semester. Each team also proposed a geologic history consistent with the mineralogy and geomorphology of the site. Students communicated their interpretations to their classmates as a formal PowerPoint presentation on the last day of class.