Adrian Broz, Greg Retallack, Briony Horgan, Lucas Silva, and Matt Polizzotto
Sequence of ~33 million year old clay-rich fossil soils (paleosols) at the Painted Hills, John Day Fossil Beds National Monument, Oregon (Photo: Jamie Francis). These paleosols are similar in mineral composition (lots of hydrated clays) and stratigraphic distribution to clay-rich areas on Mars at Mawrth Vallis, Nili Fossae, Oxia Planum, and elsewhere. Importantly, the ExoMars 2020 rover is going to Oxia Planum, which is a westward extension of the Mawrth Vallis clay layers.
Across ancient surface environments of Mars, Where are the best places to search for past signs of life? Where are you most likely to find something interesting, if it is there?
Mars offers the tantalizing prospect of being the most immediate and accessible location to test the hypothesis that life has existed elsewhere. Current and planned missions to Mars are investigating clay-rich areas (dioctahedral and trioctahedral phyllosilicate clay-rich rocks), but it is not well understood which types of clays (there are many types) are best at preserving organic matter or other biosignatures over geological time scales.
This research seeks to prioritize locations for in-situ biosignature detection (Curiosity and Mars 2020) and Mars Sample Return. Our approach is to examine clay-rich paleosols on Earth that are strikingly similar in clay mineralogy and stratigraphy to clay sequences that have been detected on Mars. Stay tuned for future updates.
Sticky, slimy stuff….
Clays are cool because:
1) Their mineralogy can record the aqueous history of a given location by constraining the temperature, pH and water:rock ratio during clay formation.
2) they have been implicated in many origin-of life theories (especially 2:1 phyllosilicates) because they facilitate spontaneous polymerization of complex macromolecules (like RNA) and provide the structural framework for concentration and preservation of these macromolecules;
and 3) They can preserve organic matter from oxidation and radiation, possibly over billions of years…