This video is called Cretaceous: Links in the Food Chain.
From CBC in Canada:
Fossils reveal cooler side of scorching Cretaceous era
Scientists discover proof of glaciers in ‘super greenhouse’ period
Last Updated: Friday, January 11, 2008 | 4:53 PM ET
One of the warmest periods in the Earth’s history wasn’t quite warm enough to keep large ice sheets from forming, scientists have discovered.
Researchers from the U.S., U.K., Germany and the Netherlands have found evidence of a 200,000-year period of widespread glaciation during the “super greenhouse” period of the Cretaceous era.
“Our research from tropical marine sediments provides strong evidence that large ice sheets indeed did exist for short periods of the Cretaceous despite the fact that the world was a much hotter place than it is today, or is likely to be in the near future,” Thomas Wagner of the U.K.’s Newcastle University said in a news release.
Earth was so warm during this period that tropical surface ocean temperatures hit highs of 37 degrees, and alligators lived in the Arctic.
The research team studied sediments found on the ocean floor near Suriname, in the northern region of South America. The sediments contained chemical-infused fossils that allowed the scientists to gather data about the seawater’s Cretaceous-era temperature.
Other researchers studied the organic molecules in the same sediments, deriving information about the water’s surface temperature.
They determined that the temperature and chemical trends in the ocean were consistent with periods of glacial formation.
The historical ice sheets are believed to have been as big as roughly 60 per cent of the size of a modern Antarctic ice cap, though the scientists said they can’t pinpoint exactly where they were located.
See also here: Ice Remained Even When Earth Was Hot.
An active volcano could be warming the West Antarctic Ice Sheet: here.