Lecture 18: Human and Preindustrial Climate

1. Lecture 18: Human and Preindustrial Climate (Chapter 15)

2. Human evolution • 4-6 Myr: • Genus Australopithecus • Walk upright DNA

3. Early mammals (lemurs)

4. Human evolution 2) 2 Myr Genus Homo erectus Stone tools • 4-6 Myr: • Genus Australopithecus • Walk upright DNA

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

6. 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.

7. Human or apes? 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.

8. 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

10. Human Evolution Climate Hypothesis savanna hypothesisvariability hypothesis Social hypothesis Technology hypothesis

11. LGM Glacial cycles & variability hypothesis Drying trend & Savanna hypothesis Human evolution Modern man Stone tools Walk upright

12. Savanna hypothesis: Early humans evolved in Africa Highlands

13. 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

14. Atmospheric CO2 Evolution Why in 100 yr cycle? Uplift weathering BLAG spreading rate,

15. Cause of the dry trend (last 20 Mys) • Uplift of East Africa highland • Uplift of Tibet Plateau • Close of Indonesian Strait (cooler Indian Ocean)

17. 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 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)

18. 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)

19. 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

20. New stone age, LGM building painting

21. Did deglacial warming lead to early faming? The spread of agriculture: starting from the Fertile Crescent

22. Did climate affect early civilization? The Black Sea flood: 7600 years ago, Diluvial hypothesis, Old World

23. Climate: Motor of Africa’s Evolution Kuper and Kropelln, 2006, Science Lat Time <8500 8500-7000 7500-6300 6300-3500

24. The collapse of Mayan: drought? Drying?

25. 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?

26. 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

27. Did land clearance induces methane changes in the last 5000 yrs

28. Faming feedback on mathene, and in turn climate?

30. End of Lecture 18

31. 3. Anthropogenic CO2 Effect Preindustrial and anthropogenic CO2 Human production of CO2: Land clearance and fossil fuels

32. CO2 Sinks • Ocean sink: has not reached the deep ocean yet • Terrestrial sink: a) regrowth of forest, b) CO2 fertilization effect

33. Ocean carbon sources and sinks

34. 4. Human effect on other greenhouse gases Preindustrial and anthropogenic CH4

36. 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)

37. Preindustrial and anthropogenic sulfates

38. Volcanic cooling

39. Anthropogenic CFC increases

40. Decline in Antarctic ozone

41. Global Greening Trend (FPAR: Fraction of Photosynthetically Active Radiation) Total CO2 Physiology Carbon fertilization Radiation Obs. >1980 Obs. – crops

42. End of Lecture 18

44. 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.