Clues in the Arctic fossil record suggest that 3-5,000 years ago, the ice sheet was the smallest it has been in the past 10,000 years
The history of the geologic era called the Pleistocene, the Ice Age era that we currently live in (though the hopeful call it the Holocene in the hope that the ice will not return) is an oscillation of the climate between a long glaciated cold mode, and a short warm period on a 100,000 year cycle:
- Ice sheets are like bulldozers. As they grow, they push rocks, boulders, clams, fossils and other debris into piles called moraines.
- By dating ancient clams in moraines, scientists have come up with a new technique for determining when glaciers were smaller than they are today.
- The technique suggests that the Greenland Ice Sheet was at its smallest point in recent history 3-5,000 years ago — information that could improve our understanding of how ice responds to climate change.
So if a moraine contains fossils from 3,000 years ago, that means the glacier was growing — and smaller than it is today — 3,000 years ago.
This is exactly what the scientists saw in Greenland: They looked at 250 ancient clams from moraines in three western regions, and discovered that most of the fossils were between 3-5,000 years old.
The finding suggests that this was the period when the ice sheet’s western extent was at its smallest in recent history, Briner said.
“Because we see the most shells dating to the 5-3000-year period, we think that this is when the most land was ice-free, when large layers of mud and fossils were allowed to accumulate before the glacier came and bulldozed them up,” he said.
We are currently in a nice warm period, but recent geologic history suggests that this is not likely to be permanent state. It's not exactly good news for civilization that the Greenland Ice Cap has grown in the last 3-5,000 years.