GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 173-11
Presentation Time: 10:35 AM


PRATT, Lisa M., Earth and Atmospheric Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405

Images of Mars from orbiting spacecraft reveal rhythmic depositional sequences in ancient sedimentary strata and in young glacial ice. Stacked bundles of couplets are a conspicuous feature of the geological record in the Arabia Terra region where couplets range in thickness from 3 to 10 meters and each couplet consists of a resistant and a nonresistant sedimentary layer. Rhythmic laying in glacial ice appears to result from differences in dust content and ice crystallinity leading to distinctive surface textures after exposure and sublimation in canyon walls and along ice margins. Additional evidence of rhythmic ice accumulation comes from radar cross sections through the north polar residual ice cap. Computer models of variations in mean latitudinal temperature for surface Mars extend back several million years from the present time and reveal a characteristic 10-to-1 pattern in the tilt of Mar’s rotational axis. Bundled deposits containing 10 couplets are inferred to correspond with obliquity-driven climate change for ice deposited in the recent past and for lithified siliciclastic sediments deposited billions of years ago. Compared to Earth, Mars expresses extreme obliquity with tilt varying by tens of degrees over a roughly 120,000-year cycle. If life was present on Mars some 4 billion years ago and biotic evolution kept pace with rhythmic climate conditions and with long-term surface desiccation then extant life on Mars could be exceptionally well adapted to both the tempo and direction of climate change. Putative martian life could be confined to subsurface refugia most of the time but capable of switching metabolic strategy and growth morphology to rapidly utilize surface resources in response to seasonal warmth and local water chemistry at or near the surface. One can only imagine Al Fischer’s enthusiasm for extending his foundational studies of sedimentary obliquity records on Earth’s to understanding the evolution of climate and, possibly, life on Mars.