[colorado tanker]

I read several papers online and the consensus seems to be the Isthmus closed 3.5 to 2.5 million years ago. I found an outlier calling it at 5 million years ago, but they have to resort to some exotic speculation as to how the closing could first cause the Pliocene warm and then cause the Holocene glacial cycles. It makes most sense to me that the closing coincided with the ending of the Pliocene warm. A couple of papers make the excellent point that this likely was not a sudden occurrence, but likely for a time was intermittent, open during interglacial periods of high sea levels and closed during glacial lows.

[muawiyah]

Just reading my Science News ~ came in today's mail ~ they have an article about the Straits of Gibraltar. They formed 5.0 to 5.5 million years ago when the Atlantic cut through the uplift that'd earlier blocked the Mediterranean from the main body of the Ocean.

This lowered aggregate Ocean levels ~ and could have "cooled things down". The Ice Age started up 2.5 million years later ~