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Steven Jacobsen Awarded CAREER Grant

July 2, 2014

The Department of Earth and Planetary Sciences congratulates assistant professor Steven D. Jacobsen on receiving a National Science Foundation Faculty Early Career Development (CAREER) award, the agency's most prestigious grant for young scholars. Jacobsen is the third EPS junior faculty member awarded major grant support in recent months. In 2007, Suzan van der Lee also received a CAREER award while Andrew Jacobson won a Packard Fellowship.

Dr. Jacobsen received his five-year, half-million dollar CAREER award for a proposal entitled "Effects of hydration on the physical properties of Earth materials from atomic to geophysical scales". His project, which will rely on a scientific team composed of undergraduates, graduate students, and one postdoctoral fellow, will examine the influence of water on the physical properties of materials at conditions reflective of the Earth's mantle.

Jacobsen's work explores the possibility that several oceans worth of water may be stored in a deep, rocky layer of Earth's mantle called the transition zone, extending from about 250 to 400 miles beneath the surface. Jacobsen, an experimental geophysicist, studies the interaction between mantle materials and water inside presses made of gem-diamond anvils. The presses simulate high-pressure, high-temperature conditions characteristic of Earth's interior at depths up to 1800 miles while the diamond anvils, which are transparent to X-ray and laser probes, uniquely enable study of the run products. Under the extreme conditions Jacobsen simulates, some silicate minerals demonstrate a remarkable ability to absorb water, not as liquid H2O, but as dissolved hydroxyl (OH). In his laboratory experiments, carried out both on the Northwestern campus and at the Advanced Photon Source of Argonne National Laboratory, Jacobsen investigates the effects of this hydration on the physical properties--such as density and compressibility--of materials found in Earth's interior.

Results from Jacobsen's studies will allow seismologists to better interpret the seismic structure of the Earth's mantle, shedding light on its variations in temperature, mineralogy, and composition. Jacobsen notes that "Some regions of the mantle are anomalously slow to seismic waves passing through from large earthquakes. Though temperature anomalies can explain most of them, a few suggest the presence of relatively high water contents". One such anomaly beneath the eastern United States, imaged by seismologist and Northwestern colleague Suzan van der Lee, suggests substantial hydration. Merging laboratory and seismic data, the two scientists hope to detect possible variations in the mantle's water content, a discovery which, according to Jacobsen, could have broad implications for the scientific understanding of our planet's development in deep geologic time: "The present-day water content of the mantle would tell us a lot about how the Earth's mantle evolved, and how Earth's original water was lost, or retained, during early planetary evolution".

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