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

Right after it cooled off in the Hadean, Earth is thought to have been mostly an ocean planet, with perhaps a few relatively small islands. 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? Historically, interpretations of the sedimentary record have largely relied on the assumption that ancient environments function like modern ones. But is this a good assumption? In this presentation, I will illustrate why it is not always the case, and how understanding the mechanics of surface 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—not only existed for most of Earth’s history but have likely gone unnoticed in the pre-vegetation archive because their deposits resemble those of 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 ancient aeolian strata. These two vignettes highlight how much surface 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 surface processes and decipher the highly fragmentary archive of Earth’s early environments.