LIFE ORIGINATED ON THE EARLY EARTH SOMETIME PRIOR TO 3.5 BILLION YEARS AGO A PERIOD WHEN THE TERRESTRIAL PLANETS IN OUR SOLAR SYSTEM EXPERIENCED BOMBARDMENT BY MANY IMPACTORS THAT PRODUCED CRATERS WITH DIAMETERS>150 KM (1). SUCH IMPACTS FACILITATE THE DEVELOPMENT OF VAST SUBSURFACE HYDROTHERMAL SYSTEMS WITHIN CRATERS WHEN WATER IS PRESENT IN THE CRUST (AS EXPECTED FOR THE EARLY EARTH MARS AND EARTH-LIKE EXOPLANETS) (2). IMPACT HYDROTHERMAL SYSTEMS HAVE BEEN SUGGESTED AS A HABITAT FOR THE ORIGIN AND EVOLUTION OF EARLY LIFE BECAUSE THEY CAN PROVIDE MICROORGANISMS WITH ENERGY SOURCES LIQUID WATER AND NUTRIENTS LEACHED FROM ROCKS OVER POTENTIALLY MILLIONS OF YEARS (3). THE 200-KM DIAMETER CHICXULUB CRATER IS EXCEPTIONALLY WELL-PRESERVED MAKING IT AN IDEAL ANALOG FOR OTHER LARGE CRATERS IN THE SOLAR SYSTEM. ITS SUBSURFACE WAS STERILIZED AT THE TIME OF IMPACT BUT NOW HOSTS A DIVERSE MICROBIAL COMMUNITY SUGGESTING LIFE INITIATED IN IMPACT CRATERS CAN PERSIST BEYOND THE TIMESCALE OF THE GENERATED HYDROTHERMAL SYSTEM (4). INTERNATIONAL OCEAN DISCOVERY PROGRAM (IODP) AND INTERNATIONAL CONTINENTAL SCIENTIFIC DRILLING PROGRAM (ICDP) EXPEDITION 364 DRILLED INTO THE CHICXULUB PEAK RING AND SAMPLED IMPACT BRECCIAS MELT ROCKS AND UPLIFTED CRYSTALLINE BASEMENT. OUR PRIOR WORK SHOWS THESE LITHOLOGIES EXHIBIT HIGH (10-30%) POROSITIES AND SECONDARY MINERALS SUCH AS CLAYS CALCITES AND FE-OXIDES/SULFIDES THAT FORMED DURING THE COOLING OF AN INITIALLY HOT (300-400 C) HYDROTHERMAL SYSTEM THAT LIKELY PERSISTED FOR>10^5 YEARS. WE WILL CONDUCT TWO TASKS TO EVALUATE THE HABITABILITY OF THE CHICXULUB CRATER HYDROTHERMAL SYSTEM (AS AN ANALOG FOR OTHER TERRESTRIAL AND EXTRATERRESTRIAL IMPACTS): UNDERSTAND THE PLUMBING AND CHEMICAL EVOLUTION OF THE HYDROTHERMAL SYSTEM AND HOW THESE FACTORS FACILITATE HABITAT DEVELOPMENT. PRELIMINARY PETROGRAPHIC OBSERVATIONS AND ELEMENTAL X-RAY MAPPING (EDS AND WDS) INDICATE THAT HYDROTHERMAL FLUIDS PERCOLATED THROUGH CRATER ROCKS VIA NARROW (SOMETIMES<100 M WIDE) FINGER-LIKE CONDUITS. WE WILL CONDUCT -CT IMAGING AND ADDITIONAL ELECTRON MICROSCOPY TO VISUALIZE FRACTURES AND PORES. IMAGING COMBINED WITH ADDITIONAL EDS WDS AND ELEMENTAL MAPPING TARGETING HYDROTHERMAL MINERALS WILL PERMIT US TO CHARACTERIZE FLUID PATHWAYS ON A MICROSCALE. OBSERVED PATHWAY SIZES WILL BE UTILIZED TO COMPUTE THERMAL GRADIENTS FROM ACTIVE CHANNELS INTO SURROUNDING ROCKS TO UNDERSTAND MICRO-TEMPERATURE DISTRIBUTIONS. ELEMENTAL MAPPING TARGETING RELATIONSHIPS BETWEEN FE-OXIDES AND SULFIDES WILL ALSO CONSTRAIN THE REDOX EVOLUTION OF THE HYDROTHERMAL SYSTEM AND ITS EFFECTS ON BIOGEOCHEMISTRY. DETERMINE WHEN REGIONS WITHIN THE CRATER BECAME THERMALLY HOSPITABLE TO LIFE. -CT ANALYSIS PROVIDES A FIRST ORDER PERMEABILITY ESTIMATE BASED ON INTERCONNECTED PORES. WE WILL BUILD ON THIS BY CONDUCTING LABORATORY PERMEABILITY MEASUREMENTS FOR REPRESENTATIVE PEAK RING LITHOLOGIES. WE WILL USE THE OBTAINED VALUES IN COMBINATION WITH OBSERVATIONS FROM TASK 1 TO MODEL THE COOLING OF THE POSTIMPACT HYDROTHERMAL SYSTEM AT NESTED SCALES. MODELED COOLING TIMESCALES WILL BE COMPARED TO TIME-TEMPERATURE CONSTRAINTS OF CRATER COOLING OBTAINED FROM PALEOMAGNETIC MEASUREMENTS AND THERMOCHRONOLOGY. THIS RESEARCH IS RELEVANT TO THE HABITABLE WORLDS PROGRAM BECAUSE IT WILL ADDRESS THE SOLICITATION GOAL OF USING EARTH HISTORY AS A GUIDE FOR DETERMINING THE PROCESSES AND CONDITIONS THAT CREATE AND MAINTAIN HABITABLE ENVIRONMENTS AND WILL ALSO IMPROVE OUR UNDERSTANDING OF THE POTENTIAL FOR [CRATER HYDROTHERMAL SYSTEMS] TO SUPPORT LIFE.

The Leland Stanford Junior University

Investigators