Lec 9 - History, Humans, Climate Flashcards
What five major developments are there in human evolution?
- branching from other apes
- bipedalism (4mya)
- Use of stone tools (2.5mya)
- Emergence of Homo genus (2mya)
- Development of large brains (2mya)
What factors likely drove human evolution?
- social factors
- tool/innovation
- climate
What 2 hypotheses explain how climate may have impacted our recent evolution?
- Savannah Hypothesis
- Variability Selection Hypothesis
What is the Savannah Hypothesis?
- human evolution was driven by long-term drying of African climate
- tropical rainforests became semiarid grassland
- fragmentation meant greater need for travel over ground, resourcefulness
- drying began 4-6mya (dated by dust)
Savannah hypothesis: what drove long-term drying in Africa?
- volcanic plateaus block wet air from Indian Ocean
- cooling of Indian Ocean meant less moisture in air
- Tibetan plateau uplift = more monsoons, drives dry air into Africa
Why doesn’t the Savannah Hypothesis explain everything?
- hominids haven’t shown preference for one biome over another, no obvious preference for savannahs
What is the Variability Selection Hypothesis?
- rapid evolution was driven because rapid habitat change favoured individuals/groups that were adaptable
Why doesn’t the Variability Selection Hypothesis explain everything?
fossil record of human evolution is pretty sparse, hard to put together a timeline of the rate of evolution
(ie hard to test hypothesis!)
When is the first evidence of agriculture?
12kya
What impacts did climate change have on early civilization?
- deglaciation is associated with permanent settlements/agriculture
- Younger Dryas would have hindered this transition
Give an example of how the Younger Dryas period might have impacted human civilization
- low latitude regions where water was scarce, the dryness in the YD
- Egyptian dynasties relying on Nile floodplain
- Mayan civilization dispersing during drought
- Anasazi peoples abandoning cliff dwellings during drought
What impacts did early H. sapiens have on our environment?
- megafauna extinctions
- cliamte (CO2 and CH4 from forest clearing and agriculture)
What might explain the extinction of megafauna at the end of the LGM?
- major climate changes - large animals = susceptible to environmental unpredictability
- overkill hypothesis - improved hunting skills/increased human populations
What evidence is there for the Overkill Hypothesis?
- timing of megafauna extinctions in Americas and Australia lines up with humans crossing over
Are GHG levels post-LGM explained by human activity?
probably not - the increase in CO2 and CH4 was too big to be explained by deforestation, burning, agriculture, rice irrigation etc
What climate changes have happened in the last 1000yrs?
- Medieval Warm Period (1000-1300)
- Little Ice Age (1350-1850) - permanent snow fields and sea ice in Europe
How does the Walker Circulation affect the coast of South America?
warm waters are pushed westward, causing upwelling
- upwelling pulls up nutrients and cool water, bringing in animals and dry weather
How do El Nino years impact people?
-no upwelling = no plankton = no fish = no mammals or birds
- warm water = more moisture = warm rains = flash floods in deserts = breeding of mosquitoes/tropical diseases
What 4 factors have caused Northern temperature changes?
- Orbital forcing
- solar variability
- volcanic activity
- GHGs
How does solar variability affect the climate?
- small (decades/centuries) timescale
- more sunspots = more radiation output
- responsible for small change in radiation
How does volcanism influence our climate?
- explosive eruptions cool climates briefly, especially near where the eruption occurred
- tends to happen along converging plate margins (mountains, not ocean islands)
