Tonian paleogeographic change as a precondition for the Sturtian Snowball Earth

During the Cryogenian Period (ca. 720–635 Ma) Earth underwent two ‘Snowball’ glaciations in which marine terminating glaciation and sea ice reached the low latitudes, with the first glaciation, the Sturtian (ca. 717–660 Ma), being the more severe and longer lasting. The drivers of global cooling that led to the Sturtian remain uncertain, but it is believed that a key factor was a decline in atmospheric CO ₂ levels due to continental breakup and Large Igneous Province (LIP) emplacement, enhancing terrestrial silicate weathering. Here we use a new detailed palaeogeographic framework and climate-ice sheet modelling to quantify how palaeogeographic changes since the late Tonian (ca. 800–720 Ma) impacted silicate weathering and CO ₂ drawdown. We find that palaeogeography-driven enhancement of silicate weathering had the potential to reduce CO ₂ levels from ca. 4000 to <500 ppm, supporting an ice-house state with continental-scale glaciation reaching ca. 40 ° latitude by 720 Ma. In addition, we find that the Franklin-Irkutsk LIP complex was located within the Intertropical Convergence Zone, where prevailing maritime easterly winds enhanced moisture availability, which would enhance basalt weathering and further increase CO ₂ drawdown. We conclude that paleogeographic changes over the Tonian primed the Earth system for snowball glaciation initiation by the Franklin LIP.