Lecture%2018:%20Human%20and%20Preindustrial%20Climate

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Lecture 18 Human and Preindustrial Climate

• (Chapter 15)

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Human evolution

• 4-6 Myr
• Genus Australopithecus
• Walk upright

DNA
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Early mammals (lemurs)
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Human evolution
2) 2 Myr Genus Homo erectus Stone tools

• 4-6 Myr
• Genus Australopithecus
• Walk upright

DNA
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Footprints from 3.6 myr ago on fresh volcanic
ash, East Africa
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Lucy 3.2 million years ago
Lucy in the Earth Discovered in 1974 by Donald
Johanson in Ethiopia, Lucy is special because
she lived so long ago (3.2 millions years) and
because almost half of her skeleton was found.
(Most fossil finds are just fragments --
sometimes a tooth or a piece of a skull.)
Johanson named her after the Beatles' song, "Lucy
in the Sky with Diamonds." Not far from the Lucy
site, another significant find was made, this one
also by Donald Johanson. Known as "The First
Family," the find consisted of many fossils that
originated from at least thirteen individuals.
The evidence indicates that the thirteen died
together some 3.2 million years ago, possibly in
a flash flood. This is the first evidence of an
ancient species living in groups.
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How do we know if an early ape-man or woman
walked upright? An examination of certain bones
-- a tibia (leg bone) or a pelvis, for example --
can reveal the answer. So can fossilized
footprints. In 1976, members of a team led by
Mary Leakey discovered the fossilized footprints
of human ancestors in Laetoli, Africa. The
footprints were formed 3.5 million years ago when
at least two individuals walked over wet volcanic
ash. The wet ash hardened like cement and was
then covered by more ash. The footprints show
that the individuals had perfect, two-footed
strides. They also reveal that one hominid was
larger than the other. And because the footprints
fall next to each other, they indicate that the
two hominids were walking side by side and close
enough to each other to be touching. Apes
sometimes walk on two legs. How, then, can we be
sure that the footprints weren't left by a couple
of apes that decided to walk upright for a few
yards? When an ape walks upright, weight is
transmitted from the heel, along the outside of
the foot, and then through the middle toes. A
human foot transmits weight from the heel, along
the outside of the foot, across the ball of the
foot, and finally through the big toe -- this is
a much more efficient way to transfer energy when
walking upright. The imprints left behind at
Laetoli clearly show the weight distribution of
true upright walkers. The footprints also look
remarkably like a human's. In fact, they looked
so human-like, some scientists had a hard time
believing that they were made by Australopithecus
afarensis (Lucy's species), the only human
ancestor known to have lived at the time.
Human or apes?
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Human evolution
3) 200 kyr Genus Homo sapiens Modern man
2) 2 Myr Genus Homo erectus Stone tools

• 4-6 Myr
• Genus Australopithecus
• Walk upright

DNA
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Climate Hypothesis savanna hypothesis
variability hypothesis
Human Evolution
Social hypothesis
Technology hypothesis
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Human evolution
Modern man
Stone tools
Walk upright
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Savanna hypothesis Early humans evolved in
Africa Highlands
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• Early Drying Trend 10 Myr
• Fragmented forest habitats into areas of trees
  interspersed with open grasslands

Long term change in Africa dust and
vegetation Drying, cooling, grass replace trees
Savanna hypothesis
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Atmospheric CO2 Evolution
Why in 100 yr cycle?
Uplift weathering BLAG spreading rate,
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• Cause of the dry trend (last 20 Mys)
• Uplift of East Africa highland
• Uplift of Tibet Plateau
• Close of Indonesian Strait (cooler Indian Ocean)

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Generally, the drying trend and human evolution
in E. Africa is consistent with Savanna
hypothesis,Butearly human were found in widely
different placesquestioning the Savanna
hypothesisThis leads to the variability
selection hypothesis

• Glaciation created cycles of cooling and drying
  in Africa, further harsh conditions
• CO2 reduction leads to a change from C3 (trees,
  shrubs) to C4 (warm grasses)

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2) Variability selection hypothesis 2 Myr

• Glaciation created cycles of cooling and drying
  in Africa, further harsh conditions
• CO2 reduction leads to a change from C3 (trees,
  shrubs) to C4 (warm grasses)

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• Early Drying Trend 10 Myr
• Fragmented forest habitats into areas of trees
  interspersed with open grasslands

Variability hypothesis
Long term change in Africa dust and
vegetation Drying, cooling, grass replace trees
Savanna hypothesis
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New stone age, LGM
building
painting
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Did deglacial warming lead to early faming? The
spread of agriculture starting from the Fertile
Crescent
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Did climate affect early civilization? The Black
Sea flood 7600 years ago, Diluvial hypothesis,
Old World
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Climate Motor of Africas Evolution
lt8500
8500-7000
7500-6300
6300-3500
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The collapse of Mayan drought?
Drying?
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Early impacts of human on climate
North America, Human impact on large
mammals. Abrupt extinction at 12,500 years
ago. Climate hypothesis? Overkill hypothesis? New
tool?
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Did land clearance induces methane changes in the
last 5000 yrs
Potential feedback High lat albedo Low lat
evaptranspiration
Disagree Why?
Agree
How early has human affected climate? Ruddiman
hypothesis
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Did land clearance induces methane changes in the
last 5000 yrs
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Faming feedback on mathene, and in turn climate?
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End of Lecture 18
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3. Anthropogenic CO2 Effect
Preindustrial and anthropogenic CO2
Human production of CO2 Land clearance and
fossil fuels
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CO2 Sinks

1. Ocean sink has not reached the deep ocean yet
2. Terrestrial sink a) regrowth of forest, b) CO2
   fertilization effect

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Ocean carbon sources and sinks
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4. Human effect on other greenhouse gases
Preindustrial and anthropogenic CH4
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Sources of Sulfate (SO2) aerosol
Generation smokestacks emit gas sulfur dioxide
(SO2) as a by-product of smelting operations in
furnaces and from burning of coal. SO2 reacts
with water vapor and is transformed ionto sulfate
particles, called sulfate aerosols, saying in the
lower atmosphere Direct effect block incoming
radiation as a cooling effect Indirect effect
acts as nuclei for cloud formation, net effect
uncertain (cooling for shortwave, but warming for
long wave as a cloud)
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Preindustrial and anthropogenic sulfates
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Volcanic cooling
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Anthropogenic CFC increases
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Decline in Antarctic ozone
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Global Greening Trend
(FPAR Fraction of Photosynthetically Active
Radiation)
Total CO2
Physiology Carbon fertilization
Radiation
Obs. gt1980
Obs. crops
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End of Lecture 18
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Lucy 3.2 million years ago
Lucy in the Earth Discovered in 1974 by Donald
Johanson, Lucy is special because she lived so
long ago (3.2 millions years) and because almost
half of her skeleton was found. (Most fossil
finds are just fragments -- sometimes a tooth or
a piece of a skull.) Johanson named her after the
Beatles' song, "Lucy in the Sky with Diamonds."
Not far from the Lucy site, another significant
find was made, this one also by Donald Johanson.
Known as "The First Family," the find consisted
of many fossils that originated from at least
thirteen individuals. The evidence indicates that
the thirteen died together some 3.2 million years
ago, possibly in a flash flood. This is the first
evidence of an ancient species living in groups.