Loophole for snowball Earth

A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA

“…The refugia hypothesis contends that eukaryotes and prokaryotes survived in some unknown refugia where conditions remained more equitable and repopulated the postsnowball Earth from those refugia (3,5). On the basis of the available paleontological data from the Death Valley region, we do not consider the refugia hypothesis tenable.…”

“…Therefore, the microbiota must have existed during or just after the peak of ''snowball'' glaciation rather than during some ''presnowball'' glacial buildup (2,3) because the ice had reached low latitudes by this time. The fossil evidence does not support a major mass mortality, extinction of benthic or planktonic organisms (1,2,5,37), or any other dramatic changes in the biosphere. The carbonate unit microbiota is similar to microbiotas found in the strata that immedi- ately predate the glaciation (Fig.…”

“…5) and elsewhere (4). It is well known that several key clades of eukaryotic autotrophs (e.g., algae) and heterotrophs (e.g., testate amoebae) predate the first severe Neoproterozoic glaciation (known as the Sturtian glaciation, Ϸ750-700 Ma) and postdate the last glaciation (commonly termed the Marinoan or Varanger glaciation, Ϸ600 Ma) (7,8).…”

“…3) in concert with the global precipitation of the unusual cap carbonates and perturbations in the biogeochemical cycling in the ocean. Suggested effects on the biosphere range from the speculation that most eukaryotic lineages went extinct (3) to the notion of life surviving in refugia (3,5,6).…”

Geochemical constraints on the origin of Doushantuo cap carbonates in the Yangtze Gorges area, South China

“…One of the most intriguing is the Marinoan glaciation that extended into equatorial latitudes (Evans, 2000;Hoffman and Schrag, 2002;Hoffman and Li, 2009). Most Marinoan glacial deposits are directly overlain by "cap carbonates" with peculiar sedimentary features and negative carbon isotope signatures (Kennedy, 1996;Hoffman et al, 1998;James et al, 2001;Hoffman and Schrag, 2002;Jiang et al, 2003a;Frimmel and Folling, 2004;Shields et al, 2007a, b;Zhou and Xiao, 2007;Shen et al, 2008), implying severe and rapid climatic changes which are thought to serve as an 'environmental filter' for biological evolution (Hoffman et al, 1998;Runnegar, 2000;Hoffman and Schrag, 2002). Strata above these postglacial cap carbonates contain the Earth's earliest multi-cellular organisms interpreted as early Metazoans (Xiao et al, 2002;Xiao, 2004;Yin et al, 2007;McFadden et al, 2008;Yuan et al, 2011).…”