3Section ObjectivesDescribe the climatic cycles that exist during an ice age.Identify and summarize the theory that best accounts for the ice ages.Climate during ice ages.Glacial periods.Cause of ice ages.Ice ageInternal plastic flowKettleLateral moraineMedial moraineMeltwaterMilankovitch theoryOutwash plainRoche moutonneeSnowfieldSnowlinestratified driftTerminal moraineTillValley glacier
4Climate During Ice Ages An ice age is thought to start when the average global temperatures are lowered.Studies show many cycles of advance and retreat of the continental ice sheets. Ice sheets advance during an ice age during glacial periods. Warmer temperatures in between glacial periods are called interglacial periods.
5Glacial PeriodsGlaciers cover nearly one-third of the earths land surfaces during one of the last glacial periods. Most of the glaciers were located in North America and Eurasia.Since most of the water in North America was locked up inside the ice the sea level was 140 meters lower than it is today. Canada and some mountain regions in Alaska were completely buried in ice. Large ice sheets formed all over the world and later combined and moved around the world. Various land features that were formed by the last ice age are still visible today.
6Causes of Ice AgeScientists have many theories as of why the ice ages occurred. Each theory shows how the gradual cooling and increase of precipitation caused an expansion of the glaciers.A theory now widely accepted is the Milankovitvh theory. Milutin Mulankovitch said that small normal changes in the earths orbit and tilt caused the ice ages.There are three types of periodic changes that occur to changes the path in which the earth moves around the sun. One of these three changes happen once every 100 thousand years. Milankovitch was able to calculate these three periodic changes the distribution of solar energy reaching the earths surface. Evidence from the ocean floor inside dead marine animals shells proves his theory. Scientists have found that these animal shells closely follow the cycle of cooling and warming predicted by this theory.There are many other theories , which all portray the same idea, that the ice age resulted from a change in the amount of solar energy that touched the earths surface.
7Continued…The explanations for some of these changes vary. Some theories say that these changes could have been caused by varying amounts of heat coming from the sun. Other theories say that volcanic dust blocked the suns rays from the earth etc…