Welcome to . . .

1. Welcome to . . . • Presented by Rod Benson • Earth Science Teacher • Helena High School Confused about ice ages?

2. 1 The Little Ice Age? Confused about Ice Ages? Wisconsinan Ice Age? Milankovitch Cycles? Snowball Earth?

3. 4 days at Helena High • Glaciers presentation . . .the basics • Snowball Earth Video (BBC) with WS • Presentation: Ice Ages • Snowball Earth • Ice Ages . . .When? and Why? • Presentation: Impact on Montana • Glacial Lake Missoula • Flathead Lake • Path of the Missouri River

4. 1. Sources 2. Brief Intro to the Snowball Theory 3. When were there ice ages? 3. Possible causes? 4. How do they know (evidence)? 5. Feedback Cycles 2 Today’s Presentation NEXT: Sources

5. Primary Sources • Ice Ages: Solving the Mystery (1979) • The Two-Mile Time Machine (2000) • Snowball Earth (2003) • Frozen Earth (2004) • Ice Ages and Astronomical Causes (2000) • Maureen Raymo of Boston University • www.moraymo.us/ • Snowball Earth Web Site • www.snowballearth.org Next: Quick history

6. Theories about Ice Ages • 1800s . . . Agassiz • Consensus that there were ice ages • 1900’s • Consensus that Milankovitch Cycles influence the timing of ice ages. • Today • Snowball Earth Theory • Many unsolved mysteries, new questions NEXT: Snowball Earth

7. 4 When were there ice ages? The Snowball Earth Theory Graph courtesy of snowballearth.org

8. Courtesy of Scientific American Magazine

10. Paul Hoffman dropstone layer Dan Schrag Courtesy of snowballearth.org

11. Glacier ocean Mud

12. Snowballearth.org

13. Clouds Snowball atmosphere: Cold, dry, clear. . . CO2 builds up Rain + CO2 Vapor (Acid Rain) Dissolves Rock (calcium, etc. into ocean) Ice Water Calcium Carbonate forms

14. Carbonate layer For more about the Snowball Earth Theory go to snowballearth.org NEXT: more recent ice ages

15. 4 When were there ice ages? When were there "ice ages"? NEXT: the past 50 my

16. Global Cooling Starts ~50 million yrs. ago

17. The most recent ice epoch • Began ~3 mya • Cooling started ~50 mya (Himalayas?) • 15-20+ glaciations (“ice ages”) • About once every 100,000 years (recently) • Currently in an “interglacial period” NEXT: the last 4 glaciations

18. Kansan • The last 4 glaciations (“ice ages”) • Thousands of yrs. to develop (ice grew southward) • Last one peaked about 20,000 years ago. Nebraskan Illinoian Wisconsin • We have enjoyed 8,000 years of warm, stable climate. NEXT: 18,000 years ago

19. Laurentide Ice Sheet NEXT Polson Moraine Map Courtesy of Chris Scotese PALEOMAP Project www.scotese.com

20. Courtesy of William Bowen Cal Tech Polson Moraine (not caused by the ice sheet)

21. Many Glacier area Courtesy of Google Earth NEXT: Little Ice Age moraine

22. NEXT: Central Park Little Ice Age 1250-1850? 1650-1850? Courtesy of U.S.G.S.

23. NEXT: spreading centers Striations caused by the ice sheet a.k.a. “continental glacier”

25. Deglaciation of the Laurentide Ice Sheet This was our last “glacial cycle” (a.k.a. “ice age”)

26. What causes ice ages? • A. Position of Continents • B. Uplift of land • especially the formation of Himalayas • C. Changes in Earth-Sun relationship? • Called “Milankovitch Cycles” • D. Reduced CO2 in atmosphere? • Not well-understood NEXT:. How do we know “when”?

27. One theory Nebraskan Kansan Wisconsinan Illinoian

28. Milutin Milankovitch 1879-1958 • He “did the math”. • Started calulations in 1912 • Published in 1930 • Consensus since the 1970’s

29. Wobble of axis He calculated how much sunlight was received at various latitudes at various times of the year. Experts think summer insolation at 65 N is the key.

30. Tilt of Axis Graph Varies from 22.1 degrees to 24.5.

31. Matches obliquity cycle. Not so simple; controversial. Courtesy of Globalwarmingart.com NEXT: Eccentricity

32. This doesn’t make sense to scientists. Currently near A minimum. Muller’s idea “The 100 kyr problem” Next: 1976

33. Graph of isotopic measurements made on two Indian Ocean cores in 1976 led to confirmation of the astro- nomical theory of the ice ages (Imbrie) BACK to causes

34. Richard Muller is “rocking the boat” • Professor of Physics at UC Berkeley • Author of Ice ages and Astronomical Causes • 1993: Tilt of Earth’s orbit changes over 100,000 year cycle (varies by 2.5 degrees) • Does Earth enter area where ET dust blocks some of Sun’s energy? • http://muller.lbl.gov • BACK

35. Land at pole contributes to the onset of an ice age 250-350 mya

36. 4 When were there ice ages? Alfred Wegener's Evidence

37. BACK to causes This is favorable today.

38. Evidence that tells when . . . • Geology • Ice cores • Sea-floor sediment cores • Isotope analysis is huge in both types of cores • Coral reefs (Barbados)

39. Microscopic shelled critters • “Foraminifera”

40. Isotope Analysis 99.8 % of Oxygen is O-16 00.2 % is O-18 0-16 is higher here during Ice Age * O-16 O-18 * O-18 is higher than normal in shells during Ice Age

41. JOIDES Resolution

42. Last Polar Reversal 790,000 years ago

43. NEXT • Feedback Cycles

44. The Uplift-Weathering Hypothesis

45. Formation of the Himalayas Higher land better sustains glaciers Increases precipitation Alters global weather patterns (jet streams, etc.) Increases chem. weathering Removes CO2 From air Weakens Earth’s Greenhouse Effect BACK

46. Do carbon dioxide levels change Earth’s temperature? Change in Eccentricity (100,000 year Cycle) ? Change in Carbon Cycle (less CO2 ) Global Cooling NEXT: Does global cooling change the carbon dioxide levels?

47. Drier air Stronger ice age winds Ice Grows More dust in air Decreased Greenhouse effect Fertilize algae Algae remove CO2 Also, colder water can dissolve more CO2

48. BACK

49. Feedback Mechanisms(some examples) A simple feedback mechanism: Global cooling starts an ice age White ice reflects more sunlight atmosphere Gets colder Opposite?

50. More CO2 Global warming CO2 in ocean ends up as CaCO3 On ocean floor More evaporation More precipitation More calcium in ocean CO2 scrubbed from atmosphere Increases weathering