Chapter 20 The Holocene

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?

Present 11,600 ybp

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

Younger Dryas 14,680 years ago 13,000 years ago Climates warmed in a decade 13,000 years ago Rapid cooling Younger Dryas Lasted through 11,600 years ago

Global Warming Terminal moraine Southern New Zealand during the Younger Dryas cooling event

End of the Ice Age Prairie potholes Depressions formed from remnant mounds of ice

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

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

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

Migrations Clovis hunters Fluted spear point

Mass Extinction Large mammal extinction La Brea tar pits 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

Mass Extinction Overkill hypothesis Climate change Human hunting may have led to a mass extinction of large mammals Climate change Rapid change Younger Dryas Habitat change Grasslands changes to prairies

Agriculture Hypsithermal Interval Agriculture developed 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

Climate Fluctuations Tree rings Non-tropical areas Annual rings Bristlecone pine 4600 years old Methuselah

Climate Fluctuations Cooling: cold intervals Medieval Warm Period 5800–4900 years ago 3300–2400 years ago 900–700 years ago Medieval Warm Period Viking expansion

Climate Fluctuations Little Ice Age Glaciers expanded Short summers Ended ~1850

Climate Fluctuations Droughts also occurred Dunes Pine tree rings

Sea Level Coastlines changed Glaciers retreated Lithospheric rebound Great Britain Coasts uplifting

Sea Level Subsidence Peripheral bulge Produced by nearby glacier Southern Great Britain Northeastern US

Sea Level Transgression Regression Lagoonal complexes transgress over coastal plain sediments New Jersey Regression High sediment supply is causing coast to move offshore Texas

Global Warming CO2 has increased since the Industrial Revolution

Global Warming Temperatures have increased Models predict continued increase in temperature Increase depends on CO2 concentrations

Global Warming Warming leads to glacial melting Mt. Kilimanjaro, 1993 and 2000

Global Warming Many impacts Migration Change in precipitation Desertification Changes in plant communities Sea level change

Global Warming Sea level may rise 50 cm by 2100 Antarctic ice cap may expand from increased snowfall Or ice cap may collapse

Global Warming Would also flood wetlands Normally marsh would migrate with coastal change Blocked by barriers

Global Warming Flooding in Venice 1990