Why was there a Neoproterozoic Snowball Earth?

Snowball Earth is a nickname for the Cryogenian Period, 717 to 635 million years ago, when glaciers extended well into tropical latitudes. Such extreme planetary chilling has been blamed on increased carbon sequestration by life in the sea, by chemical weathering of volcanic rocks, and by life on land. Discovery of pre-Cryogenian paleosols containing a diverse eukaryotic soil microbiome including fungi and testate amoebae suggests that glacial expansion was caused by increased carbon consumption due to evolutionary advances in life on land. Microfossils in paleosols of the 776-729 Ma Chuar Group of Arizona include cyanobacterial microfossils (Siphonophycus typicum and Polytrichoides linearis), fungal hyphae (Tortotubus protuberans and Mucorites ripheicus), fungal vesicles (Palaeoglomus strotheri), and testate amoebae (Cycliocyrillium torquatum, Trigonocyrillium hor-odyskii, Melanocyrillium hexadiadema, Bonneia dachrychares, and Carabinia granosa). Also found were fragments of enigmatic lichen-like, multicellular thalli described here as Porterra dehlerae gen. et sp. nov. A few fossils by themselves did not change the world, but Chuar and other paleosols reveal transition from low productivity Gypsids to high productivity Calcids. Increased biomass, soil respiration, and nutrient depletion documented from chemical analyses of paleosols accelerated silicate weathering and carbon consumption, diminishing CO2 greenhouse, and ushering in Snowball Earth.

Automated summary

Snowball Earth, also known as the Cryogenian Period, refers to a time period from 717 to 635 million years ago when glaciers covered even tropical latitudes. The extreme cooling of the planet has been attributed to increased carbon sequestration by marine life, chemical weathering of volcanic rocks, and advances in life on land. The discovery of pre-Cryogenian paleosols containing a diverse eukaryotic soil microbiome suggests that glacial expansion was driven by increased carbon consumption due to evolutionary advances on land. This transition from low productivity Gypsids to high productivity Calcids, as revealed by paleosol analysis, led to accelerated silicate weathering, carbon consumption, and a decrease in CO2, ultimately resulting in Snowball Earth.