Welcome to... Presented by Rod Benson Earth Science Teacher Helena High School

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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

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

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 Snowball Earth Web Site Next: Quick history

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

When were there ice ages? 4 Graph courtesy of snowballearth.org

Courtesy of Scientific American Magazine

Dan Schrag Paul Hoffman dropstone layer Courtesy of snowballearth.org

Glacier Mud ocean

Snowballearth.org

Vapor Clouds Rain + CO 2 (Acid Rain) Dissolves Rock (calcium, etc. into ocean) Calcium Carbonate forms Water Ice Snowball atmosphere: Cold, dry, clear... CO 2 builds up

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

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

Global Cooling Starts ~50 million yrs. ago

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

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

Map Courtesy of Chris Scotese PALEOMAP Project NEXT Polson Moraine Laurentide Ice Sheet

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

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

Courtesy of U.S.G.S. NEXT: Central Park Little Ice Age ? ?

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

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

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 CO 2 in atmosphere?D. Reduced CO 2 in atmosphere? –Not well-understood NEXT:. How do we know “when”?

Wisconsinan Illinoian KansanNebraskan One theory

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

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.

Tilt of Axis Varies from 22.1 degrees to Graph

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

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

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

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? BACK

Land at pole contributes to the onset of an ice age mya

When were there ice ages? 4

BACK to causes This is favorable today.

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

Microscopic shelled critters “Foraminifera”

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

JOIDES Resolution

Last Polar Reversal 790,000 years ago

NEXT Feedback Cycles

The Uplift-Weathering Hypothesis

Formation of the Himalayas Higher land better sustains glaciers Alters global weather patterns (jet streams, etc.) Increases precipitation Increases chem. weathering Removes CO 2 From air Weakens Earth’s Greenhouse Effect BACK

Change in Eccentricity (100,000 year Cycle) Change in Carbon Cycle (less CO 2 ) Global Cooling ? NEXT: Does global cooling change the carbon dioxide levels? Do carbon dioxide levels change Earth’s temperature?

Ice Grows Drier air Stronger ice age winds More dust in air Fertilize algae Algae remove CO 2 Decreased Greenhouse effect Also, colder water can dissolve more CO 2

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

More CO 2 Global warming More evaporation More precipitation CO 2 scrubbed from atmosphere Increases weathering More calcium in ocean CO 2 in ocean ends up as CaCO 3 On ocean floor

BACK Change in Eccentricity (100,000 year Cycle) Change in Carbon Cycle (less CO 2 ) Global Cooling ? Finally

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