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THE ICE AGE

A. INTRODUCTION

Last ice age began ~2.5 MYBP

Image credit: NOAA Paleoclimatology Program/Department of Commerce

B. GLACIALS AND INTERGLACIALS

Image credit: Robert A. Rohde, Global Warming Art

Numerous large temperature changes

• glacials: cold periods of ice sheet growth

• interglacials: warm periods of ice sheet retreat

Evidence

• ocean sediment cores: marine oxygen isotope record

• ice cores

Events

• Wisconsin glacial - most recent; 115,000 YBP - 10,000 YBP

• Late Wisconsin - 25,000 YBP - 10,000 YBP

• Sangamon interglacial - 130,000 - 115,000 YBP

• Illinoian glacial

• all earlier glacials/interglacials referred to by their isotope stage

C. POSSIBLE CAUSES OF CLIMATE CHANGE

Plate Tectonics

• changing geographic location of the continents

Uplift of the Himalayas

• changes in atmospheric circulation

• intensification of Asian monsoon

• increased chemical weathering - change in atmospheric composition

Changes in Atmospheric Composition

Data source: Barnola, J.M. D. Raynaud, C. Lorius & N.I. Barkov (2003) Historical CO2 record from the Vostok ice core. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

Astronomical Theory

• shape of the earth's orbit

Images: NASA Earth Observatory

• tilt of the earth's axis

Image credit: NASA Earth Observatory

• "wobble" of the earth's axis

Image credit: NASA Earth Observatory

Changes in Ocean Circulation

Image credit: NASA

D. SUMMARY

• climate - externally driven force

• drives processes of degradation:

  • weathering: weakens the resisting framework

  • water & ice: erode & deposit material, sculpting, and ultimately wearing down the continental surface