Snowball Earth

[lpetrich]

 Snowball Earth
The story of Snowball Earth - interview with geologist Paul Hoffman

The name describes its appearance from outer space — a glistening white ball. The ice surface is mostly coated with frost and tiny ice crystals that settled out of the cold dry air, which is far below freezing everywhere. Gale-force winds howl in low latitudes. Beneath the floating ice shelf, a dark and briny ocean is continually stirred by tides and turbulent eddies generated by geothermal heat slowly entering from the ocean floor.

• 650 - 635 Mya:  Marinoan glaciation
• 715 - 680 Mya:  Sturtian glaciation (may be more than one)
• 2.5 - 2.1 Gya:  Huronian glaciation, a possible earlier snowball phase

The evidence for these glaciations is characteristic glacial deposits at low latitudes, deposits that include "dropstones" released by melting glaciers and icebergs.

On top of the glacial deposits is thick layers of carbonate rocks.

Here is the most likely scenario.

It started when the Earth suffered a runaway Ice Age. More ice and snow means brighter land which means more light reflected away. This makes the Earth colder and gives it more snow and ice. The process stops when the Earth is entirely iced over.

Volcanoes still released carbon dioxide into the atmosphere. But no liquid water meant no weathering and no CO2 removal. So this CO2 accumulates in the air and makes a stronger and stronger greenhouse effect until the ice melts. When it does, some of this CO2 gets deposited as carbonate rocks.

Snowball Events for Tidally Locked Planets? noting No Snowball on Habitable Tidally Locked Planets with a Dynamic Ocean - IOPscience - they won't go into a snowball state.

 

[Loren Pechtel]

We snowballed three times? I was only aware of one.

 

[DBT]

 Snowball Earth
The story of Snowball Earth - interview with geologist Paul Hoffman

The name describes its appearance from outer space — a glistening white ball. The ice surface is mostly coated with frost and tiny ice crystals that settled out of the cold dry air, which is far below freezing everywhere. Gale-force winds howl in low latitudes. Beneath the floating ice shelf, a dark and briny ocean is continually stirred by tides and turbulent eddies generated by geothermal heat slowly entering from the ocean floor.

• 650 - 635 Mya:  Marinoan glaciation
• 715 - 680 Mya:  Sturtian glaciation (may be more than one)
• 2.5 - 2.1 Gya:  Huronian glaciation, a possible earlier snowball phase

The evidence for these glaciations is characteristic glacial deposits at low latitudes, deposits that include "dropstones" released by melting glaciers and icebergs.

On top of the glacial deposits is thick layers of carbonate rocks.

Here is the most likely scenario.

It started when the Earth suffered a runaway Ice Age. More ice and snow means brighter land which means more light reflected away. This makes the Earth colder and gives it more snow and ice. The process stops when the Earth is entirely iced over.

Volcanoes still released carbon dioxide into the atmosphere. But no liquid water meant no weathering and no CO2 removal. So this CO2 accumulates in the air and makes a stronger and stronger greenhouse effect until the ice melts. When it does, some of this CO2 gets deposited as carbonate rocks.

Snowball Events for Tidally Locked Planets? noting No Snowball on Habitable Tidally Locked Planets with a Dynamic Ocean - IOPscience - they won't go into a snowball state.

Tidally locked planets orbiting red dwarfs, etc, may have trouble holding onto an atmosphere because of a weak or absent magnetic field?

 

[lpetrich]

Tidally locked planets orbiting red dwarfs, etc, may have trouble holding onto an atmosphere because of a weak or absent magnetic field?

That can indeed be a problem for such planets, but that's a separate issue.

There is also the issue of why our planet has its amount of water and atmosphere on its surface. That is because some exoplanets have densities that are consistent with their having superdeep oceans - a couple hundred or even a couple thousand kilometers deep. The Earth's average ocean depth is 3.7 km, and averaged over the Earth's entire surface, it is 2.6 km. The Earth is about 71% covered by its ocean. The Earth's highest elevation above sea level is of Mt. Everest's peak, at 8.8 km, and its lowest depth is of the lowest spot of the Mariana Trench, or 11 km.

Venus and Mars started out with roughly similar amounts of surface water, though they have lost much of it. Estimates of the Earth's interior water are very hand-wavy, and I've seen estimates like roughly 10 times the surface water, and that is likely also true of Venus and Mars.