GEOG 2RC3 Lecture Notes - Louis Agassiz, Ice Age, Geologic Time Scale
17 Jul 2014
School
Department
Course
Professor
Document Summary
Several advances (glacial periods) and retreats (interglacial periods) of continental ice sheets in northern hemisphere beginning one million ya. Bp (before present) up to 10,000 years bp. Holocene epoch- the current period on the geologic time sale; began 10,000 ya. Most recent glacial period known as the wisconsin ice age which began 67k ya and ended 12. 5k ya. Maximum extent of wisconsin ice sheet reached 18-25k ya. Scientific knowledge regarding ice ages is quite recent-early theories proposed by louis agassiz and charles lyell between 1830 and 1860. Theories regarding the causes of ice ages focus on the factors which cause variation in the amount and distribution of sunlight (solar energy) reaching the earth"s surface. In each case, these factors affect the earth"s orbit. Three cycles of the earth"s orbit: precession, tilt. Earth"s orbit around the sun changes from more elliptical to less elliptical (more oval) Affects the timing of the seasons: cycle lasts 19-23k years.
