HR: 1340h
AN: B33B-0267    [Abstracts]
TI: Laboratory Studies of Survival Limits of Bacteria During Shock Compression: Application to Impacts on the Early Earth
AU: * Willis, M J
EM: mjwillis@gps.caltech.edu
AF: Seismological Laboratory (252-21), California Institute of Technology, Pasadena, CA 91125 United States
AU: Ahrens, T J
EM: tja@gps.caltech.edu
AF: Seismological Laboratory (252-21), California Institute of Technology, Pasadena, CA 91125 United States
AU: Bertani, L E
EM: lebert@its.caltech.edu
AF: Division of Biology (156-29), California Institute of Technology, Pasadena, CA 91125 United States
AU: Nash, C Z
EM: nascz@gps.caltech.edu
AF: Division of Geological and Planetary Sciences (170-25), California Institute of Technology, Pasadena, CA 91125 United States
AB: Shock recovery experiments on suspensions of 10$^{6}$ mm$^{-3}$ {\it E. coli} bacteria contained in water-based medium, within stainless steel containers, are used to simulate the impact environment of bacteria residing in water-filled cracks in rocks. Early Earth life is likely to have existed in such environments. Some 10$^{-2}$ to 10$^{-4}$ of the bacteria population survived initial (800 ns duration) shock pressures in water of 219 and 260 MPa. TEM images of shock recovered bacteria indicate cell wall indentations and rupture, possibly induced by inward invasion of medium into the cell wall. Notably cell wall rupture occurs dynamically at $\sim$0.1 times the static pressures {\it E.coli} have been demonstrated (Sharma et al., 2002) to survive and may be caused by Rayleigh-Taylor instabilities. We infer the invading fluid pressure may exceed the tensile strength of the cell wall. We assume the overpressures are limited to the initial shock pressure in water. Parameters for the Grady & Lipkin (1980) model of tensile failure versus time-scale (strain rate) are fit to present data, assuming that at low strain rates, overpressures exceeding cell Turgor pressure require $\sim$10$^{3}$ sec. This model, if validated by experiments at other timescales, may permit using short loading duration laboratory data to infer response of organisms to lower shock overpressures for the longer times (10$^{0}$ to 10$^{3}$ s) of planetary impacts. An Ahrens & O'Keefe (1987) shock attenuation model is then applied for Earth impactors. This model suggests that Earth impactors of radius 1.5 km induce shocks within water-filled cracks in rock to dynamic pressure such that stresses exceeding the survivability threshold of {\it E. coli} bacteria, to radii of 1.7-2.6$\times$10$^{2}$ km. In contrast, a giant (1500 km radius) impactor produces a non survival zone for {\it E. coli} that encompasses the entire Earth.
UR: http://www.gps.caltech.edu/$\sim$mjwillis/research/bugbuster.html
DE: 9619 Precambrian
DE: 5420 Impact phenomena (includes cratering)
DE: 3944 Shock wave experiments
DE: 1630 Impact phenomena
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting