OCGC Seminar - Did the Franklin LIP cause Snowball Earth?


Dr. Francis Macdonald
Department of Earth and Planetary Sciences, 
Harvard University


Thursday, March 3rd
11:30 a.m.  

Gamble Hall
615 Booth Street
Geological Survey of Canada



The events that led to the initiation of Snowball Earth remain poorly understood. Proposed scenarios include the oxidation of a methane-rich atmosphere, a biological innovation that led to an increase in organic carbon burial and anaerobic remineralization, or an increase in global weatherability due to the break-up of the supercontinent Rodinia and a paleogeography with a preponderance of low latitude continents. I propose instead that the Sturtian Snowball Earth was initiated by the eruption of the Franklin Large Igneous Province (LIP), which caused an increase in planetary albedo from the conversion of volcanic SO2/H2S emissions to tropospheric and stratospheric sulfate aerosols.

The Franklin LIP is the largest preserved Neoproterozoic LIP and one of the largest in Earth History. Additionally, the Franklin LIP was emplaced at equatorial latitudes with associated sills that invaded epicontinental sulfur evaporite basins, potentially maximizing environmental effects. Sills associated with the Franklin LIP show evidence of massive sulfur entrainment. The most precise geochronological constraints on the Franklin LIP overlap with the onset of the Sturtian Snowball Earth glaciation, which began between 717.5 and 716.3 Ma and marked the first glaciation in over 1.5 billion years.

Mafic LIPs form fire fountains that can erupt for decades and drive turbulent, volatile-rich convective plumes with heights >15 km. Atmospheric modeling suggests that aerosols are more likely to penetrate the stratosphere when the background climate is cold. This means that a pre-Snowball climate where CO2 had already been drawn down to low levels would be more vulnerable to cooling via volcanic stratospheric aerosol injection, and that once a volcanic eruption began, a positive feedback would occur: surface cooling by aerosols lowers the tropopause height, making it easier for subsequent eruptions to penetrate the tropopause and hence recharge the aerosol content of the stratosphere. If a single, large fire fountain, or multiple overlapping fire fountains associated with the Franklin LIP, persisted at the equator over decades, the growth of sea-ice may have resulted in a run-away ice albedo event and initiated the Sturtian Snowball Earth.