Cell count data from the Chicxulub crater. Grant abstract: The deep subsurface is recognised to be an environment that supports a large and diverse microbial biosphere, and yet we still know very little about how microorganisms grow in this environment, what their spatial diversity is and how this diversity is controlled by subsurface geochemical conditions. Previous research has primarily focused on deep-ocean sediments. Work in these environments has shown that geochemical interfaces are important for determining the diversity of the subsurface biosphere. Little is known about how the subsurface biosphere in marine environments compares to that in continental subsurface environments. Our laboratory will acquire core samples collected from the peak ring of the 66 million-year old Chicxulub impact structure buried beneath the Gulf of Mexico in April-May 2016 during IODP Expedition 364. This end-Cretaceous impact structure is hypothesised to have been responsible for causing the extinction of the dinosaurs and ~75% of all other life at this time. The drill core will be retrieved with microbiological contamination control to ~1.5 km depth. Thus, the drill core offers the opportunity to investigate the subsurface microbiology of a continental site and also how the microbial diversity relates to a unique, but well-defined subsurface lithologic sequence. In this project we propose to use these cores to gain new insights into the diversity of microorganisms in the subsurface. In this project we will: 1) Quantify the biomass of microorganisms through the core and correlate it to the lithologies to understand how microbial life in the continental deep subsurface is influenced by lithology, 2) Specifically investigate how microbial abundance and diversity is correlated to impact lithologies to understand how impacts can disrupt the deep subsurface biosphere, 3) Culture and use '-omics' methods such as metagenomics to understand how the functional capabilities and metabolisms of organisms correlate to the environment and lithology through the core to gain a better understanding of microbial biogeochemical processes in the deep subsurface in general and specifically in an impact crater, 4) Use the above data to understand more generally how life recolonises impact craters and how craters might provide a habitat for life despite otherwise catastrophic effects on large surface dwelling life.