Chapter 5 - Archean Lakes as Analogues for Habitable Martian Paleoenvironments

Abstract

Early in Mars’ history, life may have flourished in lacustrine environments developed during a comparatively warmer and wetter climate regime. Sustained subaqueous environments are high priority landing sites for the Mars 2020 mission, which is likely to focus on in situ analysis of geological features present in these environments, and on sample return. However, the community lacks experience investigating ancient, microbially dominated lacustrine environments, in part due to their rarity. Among the rocks that were formed during the Archean and that host biosignatures, only the Fortescue Group (2775–2630 Ma) is known to contain well-preserved lake deposits. Intervals within this group preserve extensive fluvio-lacustrine depositional facies and several categories of biosignatures recording the presence of early, microbially dominated ecosystems. The broader depositional environment of lacustrine units within the Fortescue Group, which formed on plateaus renewed by episodes of ongoing basaltic volcanism, is analogous to the broader depositional setting of paleolakes that may be encountered on Mars. Repeated lake high stands and drying events provide an analogue for climate change related to obliquity variations in early Martian environments, insights into the effect of climate changes on the lacustrine microbial biosphere, and an exploration model for taphonomic windows preserving microbial biosignatures in elements of these systems.