[Keith_McClary]

In another thread

The Earth has two naturally stable states, massive glaciation about -10C from today's temperatures and ice free Hothouse +10C from today's temperatures. Those numbers are not exact because today's temperature is a moving target. When the world is in one of those two states it tends to stay there for periods of not less than 100,000 years and frequently for millions of years or even tens of millions of years.

Our climate depends a lot on the current peculiar arrangement of the continents, with an enclosed Arctic sea and some land at the south pole to anchor the ice cap. Over time scales of tens of millions of years this has changed

so it is not clear that we can make such inferences about stable states from the geological record.

Suppose for example that the earth's 25% land was around the poles with ocean between the 49th parallels. Or alternatively, suppose the land was all between the 15th parallels. SciFi scenarios perhaps, but it can be instructive to consider extreme cases. In the latter case it's hard to see how the glaciation state could arise.

[Tanada]

I suggest you read up on Snowball Earth, when very little land was at the poles and the world froze over almost completely.

[dorlomin]

I suggest you read up on Snowball Earth, when very little land was at the poles and the world froze over almost completely.

The sun was producing about 10% less light.

[Tanada]

I suggest you read up on Snowball Earth, when very little land was at the poles and the world froze over almost completely.

The sun was producing about 10% less light.

Current research indicates it might have happened three different times. The last time was about 600 million years ago when the sun was about 4% dimmer than today, not 10%.