Abstract: 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.

Bio: Dr. Lapôtre is an Assistant Professor in Earth & Planetary Sciences at Stanford. His research focuses on the mechanics of sedimentary and geomorphic processes that shape planetary surfaces, and aims to unravel what landforms and rocks tell us about past hydrology, climate, and habitability. He earned a BS in Geophysics, MS in Environmental Science & Engineering, and MS in Geophysical Engineering from the U. Strasbourg, France, and a MS in Planetary Science and PhD in Geology from Caltech. During his PhD, he was part of the NASA Curiosity rover team. Before joining Stanford, he was a John Harvard Distinguished Science Fellow at Harvard. He was the 2021 recipient of the American Geophysical Union Luna B. Leopold Early Career Award.