Snowball Earth theory: Weak tides contributed to long ice ages and glaciation – study | Science | News

The Earth has endured many drastic periods of change in its 4.5-billion-year history, including changes to its climate and at least five extinction events. Two such periods occurred between about 715 to 630 million years ago when scientists have proposed a blanket of ice and snow covered the globe. This is popularly known as the Snowball Earth, although and how the planet’s climate reversed from it.

A team of scientists, including researchers from the University of Bangor in the UK, the University of Lisbon in Portugal, and Oregon State University and Northwestern University in the US, have now explored the impact of tides on this icy period.

The researchers employed a numerical tide model to reconstruct what the planet may have looked like 725 million years ago.

Their findings were presented on December 4 in the journal Nature Communications.

At the time of the prolonged ice ages, their study found ocean tides were much weaker than they are today.

On average, the tides were between 10 and 20 percent lower than today.

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“The lack of tidal energy may therefore have been one process leading to the very long duration of the glaciations.

“The research pushes back the limits for our understanding of the tides, providing the first explicit estimate of tidal energetics during the period, the team has opened doors for further investigations into a very different time in Earth’s history.”

Scientists have proposed at least two Snowball Earths have occurred during the Cryogenian period 715 to 630 million years ago.

By some estimates, the first period – the Sturtian – lasted for 57 to 58 million years while the other – the Marinoan – lasted about 15 million years.

The hypothesis is based on geological evidence of glaciers found near the planet’s equator.

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Because of the curvature of the planet and how it bulges at the equator, this region receives more energy from the Sun than locations north or south of the line.

Scientists have, therefore, proposed that if glacial ice was once present around the equator, then it must have been present everywhere else at some point.

But there are problems with the theory. Scientists have, for instance, been unable to crack how the planet left this icy state.

Physicist Richard Peltier of the University of Toronto said: “The suggestion that the Earth was once entirely covered by ice – the continents by thick ice sheets and the oceans by thick sea ice – remains somewhat contentious.”

An alternative theory to the “hard” Snowball Earth is the “Slushball Earth”.

In this case, swaths of the planet are still covered by ice but a ring of open water runs around the equator.

However, Geologist Paul Hoffman at the University of Victoria in British Columbia contested this, saying: “In the Slushball scenario, carbon dioxide would start building up very quickly, so the glaciation would be short-lived and the ice would retreat gradually. This is not what we see in the geologic record.

“We now know that the first Snowball lasted for 58 million years and that is completely inconsistent with the Slushball idea.

“Also, we see the Snowball glaciations terminate extremely abruptly and they are followed by clear evidence of a complete and abrupt climate reversal, a very hot period. That is not explained by the Slushball model.”

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