When Were the Ices Ages and Why Are They Called That?
The Ice Ages began 2.4 million years ago and lasted until 11,500 years ago. During this time, the earth’s climate repeatedly changed between very cold periods, during which glaciers covered large parts of the world (see map below), and very warm periods during which many of the glaciers melted. The cold periods are called glacials (ice covering) and the warm periods are called interglacials.
There were at least 17 cycles between glacial and interglacial periods. The glacial periods lasted longer than the interglacial periods. The last glacial period began about 100,000 years ago and lasted until 25,000 years ago. Today we are in a warm interglacial period.
How do we know?
When a glacier (or ice sheet) grows and moves across the landscape, it pushes rocks and sediments. When the glacier melts, it leaves piles of these rocks behind. The rock piles are called moraines. These moraines provide evidence that glaciers once covered large parts of the world.
Scientists also study the chemicals in ice cores from Greenland (a country in the far north) and rock deposits from the ocean floor. Those chemicals indicate what the climate was like when the ice or rocks were formed.
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