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Chapter 20The Holocene

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Guiding Questions

• Did Earth move directly from the last glacial maximum to the present glacial minimum?

• Did species that form modern plant communities evolve together?

• Have climatic changes been gradual during Holocene time?

• When did humans migrate from Eurasia to North America?

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Present

11,600 ybp

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End of the Ice Age

• Glaciers began to retreat around 15,000 years ago– Waters drained to lakes– Sea level rose– Tundra shifted northward– Deciduous trees migrated

northward

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Younger Dryas• 14,680 years ago

– Climates warmed in a decade

• 13,000 years ago– Rapid cooling– Younger Dryas– Lasted through

11,600 years ago

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Global Warming• Terminal moraine

– Southern New Zealand during the Younger Dryas cooling event

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End of the Ice Age• Prairie potholes

– Depressions formed from remnant mounds of ice

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End of the Ice Age• Vegetation changes occurred

– Southern floras were very different than today– Trees species shifted at different times– Led to changes within communities

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End of the Ice Age• Corals provide gauge for sea level changes

– Acropora palmata– Grows with sea level

• Radiocarbon, U-Th determined timing

• Corrected for tectonic change

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Migrations• Humans colonized North America

– Clovis people• Approximately 11,000 years ago

– Relied on elephants· Woolly mammoth · Mastadon

- Tundra - Eastern forests- Small ears, short trunk - Curved molars

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Migrations• Clovis hunters

– Fluted spear point

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Mass Extinction• Large mammal extinction

– 12,000–10,000 years ago– All three American

elephants– Large beavers– 5 species of horses– North American camel– Giant ground sloths– Giant armadillos

• La Brea tar pits– Preserved fauna

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Mass Extinction

• Climate change– Rapid change

• Younger Dryas

• Habitat change

– Grasslands changes to prairies

• Overkill hypothesis– Human hunting

may have led to a mass extinction of large mammals

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Agriculture• Hypsithermal Interval

– 9000–6000 years ago

– 2°C warmer than today

• Agriculture developed– Zagros Mountains

• First site

– Greek islands

• 8000 years ago

– Europe

– Northern Europe

• 6000 years ago

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Climate Fluctuations• Tree rings

– Non-tropical areas• Annual rings

– Bristlecone pine• 4600 years old• Methuselah

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Climate Fluctuations• Cooling: cold intervals

– 5800–4900 years ago

– 3300–2400 years ago

– 900–700 years ago

• Medieval Warm Period– Viking expansion

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Climate Fluctuations• Little Ice Age

– Glaciers expanded– Short summers– Ended ~1850

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Climate Fluctuations• Droughts also occurred

– Dunes– Pine tree rings

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Sea Level• Coastlines changed

– Glaciers retreated• Lithospheric

rebound

• Great Britain

– Coasts uplifting

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Sea Level• Subsidence

– Peripheral bulge• Produced by nearby

glacier

• Southern Great Britain

• Northeastern US

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Sea Level• Transgression

– Lagoonal complexes transgress over coastal plain sediments

– New Jersey

• Regression– High sediment supply is causing coast to move offshore

– Texas

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Global Warming• CO2 has increased since the Industrial Revolution

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Global Warming

• Temperatures have increased

• Models predict continued increase in temperature– Increase depends on

CO2 concentrations

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Global Warming• Warming leads to glacial melting

• Mt. Kilimanjaro, 1993 and 2000

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Global Warming• Many impacts

– Migration– Change in

precipitation• Desertification

– Changes in plant communities

– Sea level change

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Global Warming• Sea level may rise

50 cm by 2100• Antarctic ice cap

may expand from increased snowfall– Or ice cap may

collapse

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Global Warming• Would also

flood wetlands

• Normally marsh would migrate with coastal change– Blocked by

barriers

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Global Warming• Flooding in Venice

– 1990

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