Salt may have helped turn Earth into a frozen world 700 million years ago
Earth may have been pushed deeper into a global deep freeze by something surprisingly ordinary: salt. Around 700 million years ago, Earth entered periods of extreme glaciation known as Snowball Earth, when ice is thought to have spread across much or potentially all of the planet's surface. Scientists have long known that expanding ice could have helped drive this transition: As bright ice…
Around 700 million years ago, Earth experienced extreme glaciation periods known as Snowball Earth, with ice potentially covering much or all of the planet's surface. Researchers from the University of Tromsø in Norway found that salt could have played a role in amplifying the cooling during these periods. As seawater freezes, salts do not all become part of the ice.
Instead, they become increasingly concentrated in the remaining liquid trapped within the sea ice. When the ice sublimates, leaving behind salt crystals, these can accumulate in a thin layer on the surface. Laboratory experiments have shown that salt crusts on cold sea ice can reflect about 93% of incoming sunlight, compared to about 83% for fresh snow and roughly 67% for melting bare sea ice.
The researchers suggest this creates a salt-albedo feedback. High-albedo surfaces reflect more sunlight, absorb less energy, and make it easier for temperatures to fall. This process works similarly to the ice-albedo feedback, where ice spreads, reflecting more sunlight than the darker ocean it replaces, leading to further cooling.
The study, published in Climate of the Past, used a simplified climate model to explore how Earth's climate could settle into different stable states during a Snowball Earth event. The model showed that salt deposits could have led to two possible stable states: one with salt deposits and one without. The state with salt deposits was substantially colder.
Once the planet became cold enough, the process could have accelerated, making the transition to a fully frozen planet harder to stop.
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