17.3 Ice Age

What is an Ice Age? Thousands of years ago ice sheets covered much more of the Earth’s surface. Thousands of years ago ice sheets covered much more of the Earth’s surface. Ice Age: a long period of climatic cooling during which the continents are glaciated repeatedly. Ice Age: a long period of climatic cooling during which the continents are glaciated repeatedly. Several Ice Ages in Earth’s history Several Ice Ages in Earth’s history Most recent began 4 m.y.a. Most recent began 4 m.y.a.

Glacial and Interglacial Periods Glacial Period: period of cooler climate characterized by Glacial Period: period of cooler climate characterized by advancement of glaciers. Interglacial Period: Interglacial Period: period of warmer climate characterized by the retreat of glaciers. What is Earth in What is Earth incurrently?

Glaciation in N. America Glaciers covered about Glaciers covered about 1/3 of Earth’s surface during last glacial period. Sea level was as Sea level was as much as 140 m lower than it is today. Canada and Canada and mountainous regions of Alaska were once buried Alaska were once buried under ice.

Causes of Ice Ages The Milakovitch Theory The Milakovitch Theory Noticed that ice ages occurred in cycles Noticed that ice ages occurred in cycles Linked cycles to the Earth’s movement relative to the sun Linked cycles to the Earth’s movement relative to the sun

Milankovitch Theory Changes in Earth’s orbit and in the tilt of Earth’s axis cause climatic changes Changes in Earth’s orbit and in the tilt of Earth’s axis cause climatic changes (1) Eccentricity-orbit changes from nearly circular to elongated (1) Eccentricity-orbit changes from nearly circular to elongated (2) Tilt of Earth’s axis-varies b/w 22.2 degrees and 24.5 degrees (2) Tilt of Earth’s axis-varies b/w 22.2 degrees and 24.5 degrees (3) Precession-axis changes position a.k.a. “wobble” (3) Precession-axis changes position a.k.a. “wobble”

Evidence of Multiple Ice Ages Discovered in the shells of dead marine animals found on the ocean floor Discovered in the shells of dead marine animals found on the ocean floor Sediments follows the cycle of cooling and warming Sediments follows the cycle of cooling and warming