Icy Worlds

Four-million-year Marinoan Snowball Shows Multiple Routes To Deglaciation

By Keith Cowing

Status Report

PNAS

April 22, 2025

Filed under Climate change, glacier, global cooling, gobal warming, Ice Age, Marinoan Snowball Glaciation, Neoproterozoic, PNAS, snowball earth, Sturtian glaciation

Four-million-year Marinoan Snowball Shows Multiple Routes To Deglaciation — Idealized ice growth and stratigraphy at onset of snowball Earth. Note vertical exaggeration. (A) Marine-terminating terrestrial ice sheet with calving ice front prior to ice-albedo runaway into snowball glaciation. The green band shows accumulation of airfall tuff. (B) Schematic of a terrestrial ice sheet at its furthest advance flowing into the snowball sea glacier shortly after the ice-albedo runaway onset of snowball glaciation. The earliest glaciomarine sediments (dark purple) accumulate beyond the furthest advance of the ice down the foreslope. Also shown is entrainment of volcanic ash from the accumulation zone of the ice sheet to the base of the sea glacier. (C) Later in the snowball, ice has thinned due to gradual global warming. In this scenario, local sea-level fall from glacioisostatic rebound and loss of ice gravity has balanced ice thinning and tectonic subsidence, maintaining a fixed grounding line. Sediments accumulating since panel (B) are shown in light purple. (D) Idealized stratigraphies at three sections in panel (C). In 1, the lowest stratigraphic dropstones only provide a minimum constraint on onset. In 2, a conformable and unambiguous record of initial ice advance is preserved. In 3, the initial ice advance has introduced hiatus via erosion and nondeposition, precluding a direct sedimentary record of onset. — PNAS

Twice during the Neoproterozoic Era, Earth experienced runaway ice-albedo catastrophes that resulted in multimillion year, low-latitude glaciations: the Sturtian and Marinoan snowball Earths.

In the snowball climate state, CO₂ consumption through silicate weathering collapses, and atmospheric CO₂ accumulates via volcanic outgassing until a sufficiently strong greenhouse causes deglaciation.

The duration and extent of ice cover are critical for planetary habitability, both on exoplanets and on Earth where animals emerged between the two glaciations. Radioisotopic ages have defined the duration of the Sturtian glaciation to 56 Myr, but the duration of the Marinoan glaciation (4 to 15 Myr) currently has 11 Myr of uncertainty.

Here, we show that the Marinoan glaciation in Namibia lasted ca. 4 Myr with less than 10 m of vertical ice grounding line motion through glacial advance-retreat cycles. The stability of a low-latitude ice grounding line is consistent with the strong hysteresis of a hard snowball state.

The disparity in durations demonstrates different routes to deglaciation, through slower CO₂ accumulation for the longer Sturtian and radiative perturbation for the Marinoan. The short duration of the Marinoan glaciation may have been essential for the survival and evolution of animals and illustrates an additional path toward habitability on exoplanets.

Four-million-year Marinoan snowball shows multiple routes to deglaciation, PNAS (open access)

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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