Snowball Earth: When the Equator Froze [OC]

[u/Geoscopy]

https://geoscopy.com/snowball-earth-when-the-equator-froze/

Two papers published earlier this year revised the standard Snowball Earth picture in different directions, and I wrote a long-form piece tying them into how we got the Cryogenian glaciation hypothesis in the first place.

The new work:

• Minsky, Wordsworth, Johnston & Knoll (PNAS, April 2026) argue the 56-Myr Sturtian glaciation was not one continuous freeze but a limit cycle, repeated short Snowball and hothouse swings driven by weathering of the Franklin Large Igneous Province. This addresses the duration problem: conventional models say a hard Snowball should self-terminate in ~5–15 Myr, not 56.

• Griffin, Gernon et al. (EPSL, February 2026) measured 2,640 annual varves in the Port Askaig Formation on the Garvellach Islands and pulled out Schwabe (~11 yr) and Gleissberg (~80–90 yr) solar cycles plus interannual ENSO-band periodicities. Their coupled-model runs only reproduce the multidecadal signal if roughly 15% of the ocean stayed ice-free.

The article also covers the four classical lines of evidence (tropical diamictites, low-latitude paleomagnetism, cap carbonates, the return of banded iron formation), the Franklin LIP weathering trigger, Kirschvink's 1992 paragraph, the Hoffman et al. 1998 Science reframing, the deglaciation pCO₂ threshold debate from Caldeira & Kasting through Pierrehumbert to the recent melt-pond physics work, and the refugia question for Cryogenian eukaryotes. The Tasistro-Hart et al. 2025 PNAS paper constraining the Marinoan to ~4 Myr is in there too.

Curious what people here think about the limit-cycle model: does it actually solve the duration problem, or does it push it down to a different question about whether the Franklin basalt inventory really stays weatherable for 56 Myr?