Building 320, Geology Corner, Room 220 and Zoom
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Francis Macdonald's research focuses on the interactions of tectonics, climate, and biological evolution through Earth history. This work begins with geological mapping, and uses stratigraphic analysis, isotope geochemistry, geochronology, paleomagnetism, and paleontology to reconstruct paleoenvironments and tectonic histories. Recent projects have focused on Snowball Earth, the Great Unconformity, the impact of tropical mountains on global climate, and the tectonic evolution of the Americas, Africa, and Asia. Macdonald was awarded the GSA Young Scientist Award (Donath Medal) in 2014 and the AGU Early Career Award (Macelwane Medal) in 2019. He holds a B.S. in Geology from Caltech and a Ph.D. in Geology from Harvard University.
The Snowball Earth hypothesis predicts that the hydrological cycle was curtailed for millions of years, with ice-cover and low temperatures limiting silicate weathering of the continental crust. In this scenario, the deep ocean should have equilibrated with the mantle through hydrothermal exchange at mid-ocean ridges. Here we report the discovery of mantle-like Sr isotope values in marine carbonate and barite that rest directly above ca. 717-661 Ma Sturtian glacial deposits in Oman. These new data and geochemical modeling support an extreme Snowball Earth scenario with near complete ice-cover and reduced continental weathering for 56 Myr. The duration and extent of the Sturtian glaciation created a major bottleneck for the evolution of eukaryotes, clearing the way for the rise of algae and origin of animals.
For Zoom access, please email Xueyao Cheng <xc272@stanford.edu>