1. Chapter 20
The Holocene

2. 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?

3. Present
11,600 ybp

4. 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

5. 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

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

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

8. 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

9. 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

10. 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

11. Migrations
Clovis hunters
Fluted spear point

12. 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

13. 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

14. 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

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

16. 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

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

18. Climate Fluctuations
Droughts also occurred
Dunes
Pine tree rings

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

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

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

22. Global Warming
CO2 has increased since the Industrial Revolution

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

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

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

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

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

28. Global Warming
Flooding in Venice
1990