What global climate factors affect glaciation?
Glaciers can be found anywhere when the snows and frozen precipitation of long, cold winters are not completely melted during the short, mild summers. What controls the glaciation is not how much snow falls during the winter, but how much ice remains after the seasonal melting. • How have patterns of glaciation changed over Earth’s history? How do we know? ANSWER: Over the last 1 billion years, large parts of the planet were covered by glacial ice that has advanced and shrunk in cyclic periods. In fact, in the last 1.5 million years, there have been at least 20 cycles during which Earth’s ice sheets have grown to twice the size they are today and then shrunk back, depending upon global average temperatures. Large or small, glaciers leave abundant evidence of their presence, even after they have melted and the ice has disappeared. Their imprints are everywhere: the spires, or horns, of mountains such as the Matterhorn; the Great Lakes of North America; and, the boulder fields of New Eng
