Reconstructing Earth’s early subaerial environments via process-informed comparative sedimentology

Right after it cooled off in the Hadean, Earth is thought to have been mostly an ocean planet. The first substantial record of emerging land dates to the early Archean, with the recognition of sedimentary rocks laid down in subaerial environments. Deciphering that record is paramount to our understanding of how plate tectonics and life came to be. However, it is minuscule and fragmentary: only 3% of Earth’s sedimentary archive formed in the first 90% of Earth’s history. So how do we even begin to read that archive? In this presentation, I will illustrate how understanding the mechanics of sedimentary processes through modern and planetary analogs can help us fill some fundamental knowledge gaps. First, I will demonstrate that meandering rivers - which have long been hypothesized to have first evolved with the rise of land plants on Earth - have likely gone unnoticed in the pre-vegetation archive because their deposits resemble those of sandy braided rivers. Second, I will apply a lesson learned from exploring our planet’s neighbor - Mars - to windblown bedform mechanics, and leverage this new knowledge to estimate the density of Earth’s atmosphere 2.64 Gy ago from observations of aeolian strata of the Vryburg Formation (Schmidtsdrift Subgroup) in South Africa. These two vignettes highlight how much sedimentary processes have evolved throughout Earth’s history, but they have always followed the laws of physics. Together, modern environments and other planets can be used as analog experiments to better grasp the mechanics of sedimentary processes and decipher the highly fragmentary archive of Earth’s early environments.

Speaker: Mathieu Lapotre, Stanford University

Editor's Note: Stanford's listing does not show a location.  This seminar is usually held in Geology Corner, Room 220.  Please confirm before attending.