Extreme Shock Pressures: Recovery and Detection of Microfossils.

In this thesis an experimental method is utilised to test the viability and

suitability of algal microfossils in the context of simulating the shock phase of lithopanspermia. Previously, the lunar surface has been suggested as a potential receptacle and store for ejected terrestrial material following a large impact on Earth. This has led to the moon being labelled in the literature as Earth’s attic. A two stage light-gas gun is used in a series of low velocity and hy

pervelocity impacts. These shot range from 0.388 to 5.11 km s-1.

These impact velocities experimentally map to computer simulations of ejecta originating from Earth

and impacting the lunar surface. Here microfossils are loaded into a sabot and frozen. They are then fired using the light-gas gun at pre-defined velocities at a water bag target. Following the impact the water is filtered and the filtrate analysed under a scanning electron microscope.

This thesis finds a shock pressure related size effect in terms of a number of size metrics. Peak shock pressure is calculated using the Planar Impact Approximation. With this, the maximum shock pressure induced by an impact was calculated to be 13.3 GPa. Microfossil fragments were recovered following each shot but intact examples became rarer as the shot velocity was ramped up.

This study also provides a solution to a methodological problem arising from evacuation of a light-gas gun, and the consequential evaporation of liquids within a sabot. Thus a projectile design that can contain liquid at low pressure is made available here.