chapter 20
Post on 31-Dec-2015
15 Views
Preview:
DESCRIPTION
TRANSCRIPT
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?
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
– Climates warmed in a decade
• 13,000 years ago– Rapid cooling– Younger Dryas– Lasted through
11,600 years ago
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
12
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
13
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
14
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
15
Climate Fluctuations• Tree rings
– Non-tropical areas• Annual rings
– Bristlecone pine• 4600 years old• Methuselah
16
Climate Fluctuations• Cooling: cold intervals
– 5800–4900 years ago
– 3300–2400 years ago
– 900–700 years ago
• Medieval Warm Period– Viking expansion
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
– Lagoonal complexes transgress over coastal plain sediments
– New Jersey
• Regression– High sediment supply is causing coast to move offshore
– Texas
23
Global Warming
• Temperatures have increased
• Models predict continued increase in temperature– Increase depends on
CO2 concentrations
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
top related