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Colloquia & Seminars

Physics Department Colloquium
Kelvin, Pascal, and mollusk shells
Time: 3:30 PM
Place: 2241 Chamberlin Hall (coffee at 430 pm)
Speaker: Pupa Gilbert, University of Wisconsin-Madison
Abstract: NacreaEuro"or mother-of-pearlaEuro"the tough, iridescent biomineral lining the inner side of some mollusk shells, is composed of aragonite (CaCO3) tablet layers alternating with organic sheets. New Polarization-dependent Imaging Contrast (PIC) maps revealed that nacre tablets are not co-oriented, but have a broad distribution of angular orientations, as shown by the Gilbert group (1) and subsequently by many others. The angle spread is the full-width of this distribution, and was found to vary across different species, and different shell growth environments. Most interestingly, we found strong correlation between nacre tablet angle spread and environmental temperature (2), and this has far-reaching consequences nacre angle spread could be used as a thermometer. Analysis of one shell with well-established stable oxygen isotope analysis and PIC-mapping validates the nacre thermometer in one modern shell. Once validated on more shells, modern and ancient, nacre-paleothermometry could be established as the first entirely-physical, as opposed to chemical, proxy for temperature (3). But the implications of this finding are more profound if T is the temperature at which the nacre formed and AS is the measured angle spread, then the equation T=26.826+0.051 AS links environment and bio-structure. This equation suggests that one could predict a biological structure based on the environment in which the organism forms it.
1. RA Metzler, M Abrecht, RM Olabisi, D Ariosa, CJ Johnson, BH Frazer, SN Coppersmith, PUPA Gilbert. Architecture of columnar nacre, and implications for its formation mechanism. Phys. Rev. Lett. 98, 268102, 2007.
2. IC Olson, R Kozdon, JW Valley, PUPA Gilbert. Mollusk shell nacre ultrastructure correlates with environmental temperature and pressure. J Am Chem Soc in press, 2012.
3. IC Olson, PUPA Gilbert. Nacre as a temperature proxy. RSC Faraday Discussions submitted, 2012.
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