Lecture 18: Human and Preindustrial Climate

(Chapter 15)

1) 4-6 Myr:

Genus Australopithecus

Walk upright

DNA

Human evolution

Early mammals (lemurs)

1) 4-6 Myr:

Genus Australopithecus

Walk upright

2) 2 Myr

Genus Homo erectus

Stone tools

DNA

Human evolution

Footprints from 3.6 myr ago on fresh volcanic ash, East Africa

Lucy: 3.2 million years ago

Lucy in the EarthDiscovered 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.

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?

Human evolution

1) 4-6 Myr:

Genus Australopithecus

Walk upright

2) 2 Myr

Genus Homo erectus

Stone tools

3) 200 kyr:

Genus Homo sapiens

Modern man

DNA

Climate Hypothesis

savanna hypothesis variability hypothesis

Human Evolution

Technology hypothesis

Social hypothesis

Human evolution

Walk upright

Stone tools

Modern man

Glacial cycles &

variability hypothesis

LGM

Drying trend &

Savanna hypothesis

Savanna hypothesis:Early humans evolved in Africa Highlands

1) 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 S

avann

a hyp

othesis

Atmospheric CO2 Evolution

Uplift weatheringBLAG spreading rate,

Why in 100 yr cycle?

Cause of the dry trend (last 20 Mys)

1) Uplift of East Africa highland2) Uplift of Tibet Plateau 3) Close of Indonesian Strait (cooler Indian Ocean)

Generally, the drying trend and human evolution in E. Africa is consistent with Savanna hypothesis,Butearly human were found in widely different places…questioning the Savanna hypothesis

This 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)

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)

1) 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

Variab

ility h

ypoth

esis

Savan

na h

ypoth

esis

New stone age, LGM

buildingpainting

Did deglacial warming lead to early faming?

The spread of agriculture: starting from the Fertile Crescent

Did climate affect early civilization?

The Black Sea flood: 7600 years ago, Diluvial hypothesis, Old World

Climate: Motor of Africa’s Evolution

<8500 8500-7000 7500-6300 6300-3500

Kuper and Kropelln, 2006, ScienceTime

Lat

The collapse of Mayan: drought?

Drying?

North America, Human impact on large mammals.

Abrupt extinction at 12,500 years ago.

Climate hypothesis?

Overkill hypothesis?

New tool?

Early impacts of human on climate

Potential feedback:

High lat: albedo

Low lat: evaptranspiration

Agree

Disagree

Why?

How early has human affected climate? Ruddiman hypothesis

Did land clearance induces methane changes in the last 5000 yrs

Did land clearance induces methane changes in the last 5000 yrs

Faming feedback on mathene, and in turn climate?

End of Lecture 18

Human production of CO2:

Land clearance and fossil fuels

Preindustrial and

anthropogenic CO2

3. Anthropogenic CO2 Effect

CO2 Sinks

1. Ocean sink: has not reached the deep ocean yet

2. Terrestrial sink: a) regrowth of forest, b) CO2 fertilization effect

Ocean carbon sources and sinks

Preindustrial and anthropogenic CH4

4. Human effect on other greenhouse gases

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)

Preindustrial and anthropogenic sulfates

Volcanic cooling

Anthropogenic CFC increases

Decline in Antarctic ozone

Global Greening TrendGlobal Greening Trend

Total CO2

Physiology

Carbon fertilization

Radiation

Obs. >1980

Obs. – crops

(FPAR: Fraction of Photosynthetically Active Radiation)(FPAR: Fraction of Photosynthetically Active Radiation)

End of Lecture 18

Lucy: 3.2 million years ago

Lucy in the EarthDiscovered 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.