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September 2, 2016
3:00pm in PLS 1140
Amy Williams from Towson University
Physical and Molecular Biosignatures in Mars-Analogous Rocks from Iron Mountain, CA: Implications for Detection with NASA's Curiosity Rover

Abstract: Dr. Amy Williams is a geobiologist who studies the formation and preservation of physical and molecular biosignatures in Mars-analogous environments. She has worked in the extreme acid mine drainage system at Iron Mountain, CA, and with hydrothermal systems in Iceland and Alaska. For the past 8 years she has been a member of the NASA Curiosity rover science team, where she works to understand how preserved microbial organisms can be detected with the instrument suite onboard Curiosity. She is the current lead of the rover's SAM instrument thermochemolysis experiment, which can detect biogenic molecules.

September 16, 2016
3:00pm in PLS 1140
Brad Foley from Penn State
Early Earth geodynamics: Insights from convection models with grainsize evolution

Abstract: The style of Early Earth tectonics is strongly debated on both observational and theoretical grounds. From a geodynamics point of view, increasing the mantle temperature towards values representative of the Archean and Hadean is known to change mantle dynamics, and can potentially impact whether weak plate boundaries can form. Many studies find that a stagnant lid prevails on the early Earth because mantle convective stresses decrease with increasing mantle temperature. However, I use new convection models to show that this finding is a result of using an overly simplistic lithospheric rheology. With grain-damage, a theory for grainsize evolution that allows plate boundaries to form through grainsize reduction, hotter mantle temperatures do not induce stagnant lid convection. However, hotter mantle temperatures change the style and vigor of subduction, changes that may be important for explaining early Earth geochemical and petrological observations. Grainsize evolution leads to sluggish plate motions at high mantle temperatures, because higher temperatures cause rapid grain-growth. This effect can explain how early-formed mantle heterogeneities persist in the mantle for 1-2 Gyrs, as seen in observations of 142Nd and 182W from Archean rocks. The style of subduction predicted by the convection models may also be consistent with petrological observations, but future work is needed to test this.

September 23, 2016
3:00pm in PLS 1140
Melissa Trainer from NASA-GSFC
Insights on Titan's organic aerosol formation from the laboratory

Abstract: Saturn's moon Titan is enshrouded with a thick haze that is the product of the extensive organic chemistry that takes place in Titan’s N2/CH4 atmosphere. The organic aerosol that comprises the haze has been studied extensively through observation and experimental simulations, yet the exact nature of the composition or formation mechanisms are still not known. Laboratory studies in our group have explored the optical, chemical, and isotopic properties of photochemical Titan aerosol analogs to provide insight on the major components and formation mechanism that may influence aerosol production on Titan. I will review our findings and discuss implications for improved understanding of observations of Titan’s haze as well as the chemical cycle of CH4 and trace atmospheric species.

September 30, 2016
3:00pm in PLS 1140
Bob Craddock from National Air and Space Museum Smithsonian Institution
The Geologic History Of Water On Mars

Abstract: Features such as valley networks and outflow channels suggest that at one time in the ancient past Mars had liquid water on its surface. However, climate modelers have had difficulties explaining how the necessary surface conditions could have existed under "faint young sun conditions." This has led some investigators to pursue alternate interpretations of the geology, which are often ad hoc. There really is only one way to interpret the geology, and the evidence is very clear what happened. Recent analyses of lander and orbiter data have helped investigators piece together the geologic history of water on Mars, the types of climate Mars experienced through time, the amount of water that may have been present, where this water went, and even how thick the atmosphere must have been.

October 14, 2016
3:00pm in PLS 1140
Mike Ackerson from Carnegie Institution for Science
Low-temperature crystallization of granites recorded in quartz from the Tuolumne Intrusive Suite

Abstract: The granitic wet solidus is a curve in temperature, pressure and composition space below which silicate melt is not present. Based on the experimentally-determined solidus curves for granitic bulk compositions, it is often assumed that granitic mineral assemblages do not crystallize below ~650-700 °C. However, some experimental data indicate that hydrous peralkaline melts can exist in equilibrium with two feldspars and quartz to temperatures as low as 330 °C. It has yet to be demonstrated whether granitic melts exist in nature to such low temperatures. Ti-in-quartz thermobarometry of granitic rocks in the Tuolumne Intrusive Suite (TIS) of the Sierra Nevada Batholith indicates that quartz in the TIS records crystallization temperatures ~122-227 °C below the commonly accepted (traditional) granodiorite wet solidus. This observation agrees with two-feldspar thermometry of the TIS and demonstrates that for some granitic systems, the traditional granitic wet solidus is not the low-temperature limit of granitic magmatism.

October 21, 2016
3:00pm in PLS 1140
Peter Driscoll from Carnegie Institution for Science
The Evolution of the Core: Connecting Earth’s magnetic and thermal histories

Abstract: The geomagnetic field provides a unique view into the dynamics of Earth’s deep interior. Magnetic remanence preserved in ancient rocks reveals a surprisingly steady and continuous geomagnetic field as old as 4.2 Ga, with evidence for polarity reversals as far back as 2.7 Ga. We present analysis of a new paleomagnetic compilation that indicates Proterozoic reversal rates were surprisingly comparable to the Phanerozoic, including the occasional superchron period with little to no polarity change. We then model the geodynamo over the last 2 Gyr, a period that includes the nucleation of the solid inner core about 0.5 Ga, using a thermal history model as input to the dynamo model. We compare our predicted geodynamo evolution with paleomagnetic observations and discuss the implications for paleogeography at that time.

November 4, 2016
3:00pm in PLS 1140
Sarah Hörst from Johns Hopkins University
November 11, 2016
3:00pm in PLS 1140
Peter van Keken from Carnegie Institution for Science
November 18, 2016
3:00pm in PLS 1140
Ricardo Arevalo from NASA-GSFC

The coordinator for the Colloquium Series is Dr. Nicholas Schmerr. You can contact him at