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Humans and Pre-Industrial Climate Michelle Letendre, Evan Wise, Chance Snow, Mary James, Sara Smith, Cristy Echaves The black curve shows the northern.

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Presentation on theme: "Humans and Pre-Industrial Climate Michelle Letendre, Evan Wise, Chance Snow, Mary James, Sara Smith, Cristy Echaves The black curve shows the northern."— Presentation transcript:

1 Humans and Pre-Industrial Climate Michelle Letendre, Evan Wise, Chance Snow, Mary James, Sara Smith, Cristy Echaves The black curve shows the northern hemisphere temperature in a climate model.

2 Climate and Human Evolution Radiometeric dating Humans evolved in Africa

3 Evidence of Human Evolution 5 Distinctive Developments Onset of bipedalism Use of stone tools Initial branching off from primate ape Development of large brains Branching of the pre-human line into genus Homo

4 Human ancestors & chimpanzees branched off Humans evolved from a small shrew-like mammal Primitive apes evolved Appearance of Human Ancestors Molecular Biology

5 Walking Upright The development to walk is still argued today Hominins Hominidae 4.3 myr ago 3.6 myr ago

6 Use of Stone Tools A natural evolutionary development Used to butcher dead animals “killer ape” hypothesis Butchering = Diet change Cutting = Use of all the animal Stone = Digging

7 Appearance of Homo Ancestral australopithecines Paranthropus Homo erectus Stone tools and use of intellect & imagination = Frequent & vast movement

8 Brain Size Hominid Braincases Growth by Volume TypeAge (Myr ago)Braincase (cm 3 ) Homo sapiens0.2 – 01100 – 1500 Homo erectus2.4 - 1.8800 – 1000 Australopithecus4.1 - 3.1400 - 500 Braincase – part of the skull that houses the brain Braincase volume has 3x Unusually rapid compared to many evolutionary changes

9 Did Climate Change Drive Human Evolution? Savanna Hypothesis Sediments from Indian and Atlantic Ocean Support this Hypothesis


11 Atmospheric CO 2 A long term decrease in atmospheric CO 2 could have been a factor in the change in vegetation There was a change from C 3 to C 4 carbon on all continents

12 Volcanic Plateaus Vegetation shifted from forest to grassland Cooling of Western Indian Ocean

13 This may be more complicated than we think… Hominins lived in many different environments (woodlands, grasslands, river margins) This leads to a different Hypothesis… The The Variability Selection Hypothesis: Rapid evolution occurred because rapidly changing climate put new demands on our ancestors, which favored those who were more adaptable.

14 Links have been found between glaciation and the appearance of the genus Homo Pollen records from East Africa support this Hypothesis Records from the Eastern and Southern Plateaus of Africa support the hypothesis as well.

15 Problems with the Variability Selection Hypothesis… It is believed that the ice sheets would’ve had little effect on the African climate. Summer monsoons continued for millions of years. No trend toward larger or smaller oscillations.

16 Aliasing Different signals become indistinguishable when sampled, or aliases Also refers to distortions or artifacts that appear in signal reconstructions

17 Sparse Fossil Records Composed of easily dissolved calcium phosphate Bad preservation of remains in acid rich soils of rain forests Brief snapshots of human evolutionary history

18 Aliasing = Misrepresentation Specimens may not be representative of the population Depiction of inaccurate long-term trends

19 Aliasing = Misrepresentation

20 Aliasing is a Problem A formidable concern with just one sample every 100,000 years or so Erroneous indications of significant developments (e.g. first evidence of walking and use of tools) Complicates correlation of relative timing between climate changes and first use of new traits

21 Volcanic Plateaus Vegetation shifted from forest to grassland Cooling of Western Indian Ocean

22 First Evidence of Agriculture Fertile Crescent o Abandonment hunting/gathering o Domestication of: cattle, livestock, barley, etc.

23 Association of Deglaciation and Agriculture Hypothesis about cause and effect link =

24 Proposed Cause and Effect Links The changing conditions made agriculture more favorable The Younger Dryas – Climatic reversal


26 Climate change is hypothesized to be a major contributing factor to the deterioration of early civilizations

27 Changing Saharan Monsoons coincided with the movement of peoples throughout the Sahara and the development of the early Egyptian dynasties.

28 The Mayan Classic Period 300 AD-1,000 AD

29 Data Collected from lake beds and stalactites indicate severe drought events during the declining years of the Maya.


31 Anasazi

32 Climate Change and the Anasazi

33 Resource Depletion Coupled with Changing Climate

34 10,000 years ago there were fewer than 50 left 50,000 years ago more than 150 genera of mammals larger than ~100 pounds existed Megafauna comes from the ancient Greek word mega meaning “Large” and the new Latin word fauna meaning “animal” Did Humans Cause Megafaunal Extinction?

35 Australia During the most recent glaciation (est. 50,000 year ago) many marsupials and non- marsupials became extinct Just before the glaciation humans had first entered Australia through southeast asia because of the low seas The humans used fire to help hunt these animals and leads scientist to believe the humans were the primary cause of extinction

36 Climate One of the major explanation of the megafaunal extinction in North America is climate change The deglaciation caused strong summers Scientists have been critical of climate hypothesis because many of the mammals went extinct over 12,500 years ago

37 Overkill Hypothesis The idea that human hunting caused extinction of the megafauna The hunting could have been from the either from the first human arrival in America or by the first appearance of new hunting technology or strategy The first humans inhabited America 12,500 years ago. They crossed into Alaska by using land bring from Asia Around the same time, 12,500 years ago, a new technology appeared which allowed for humans to hunt bigger game

38 Criticism of the Overkill Hypothesis Were there enough people to cause extinction of the megafauna? o Large mammals have slow reproduction o Humans worked in team to drive animals to their death over step cliffs. So many animals died but only a fraction were used for food and clothing. Many carnivores went extinct but how? o With the prey that carnivores eat going extinct the carnivores would decrease their population. How did the megafauna we see today survive?

39 Black Sea Flood Hypothesis tries to explain the worldwide flood and the widespread deposit Diluvial Hypothesis

40 Early Anthropogenic Hypothesis  States that cyclic variations in CO 2 and CH 4 driven by Earth’s orbital changes during the 350,000 yrs predict a decrease in CO 2 and CH 4 but anomalies in the data show an increase in CO 2 occurring 8,000 yrs ago as well as a rise in CH 4 occurring 5,000 years ago.  Deforestation began 8,000 yrs ago leading to an increase of CO 2.  Large scale rice cultivation began in India and China 5,000 yrs ago producing higher levels of CH 4. Proposed by William Ruddiman

41 CO 2 & CH 4 Influences

42 Further Evidence for the Early Anthropogenic Hypothesis  5, 000 years ago the Monsoon weekend across the Sahara reducing CH 4 emissions from wetlands.  Arctic summers became cooler  England in 1086 was 85% arable land was pasture or crops, 15% remaining forest.  Rice irrigation began in SE Asia 7,000-6,000 years ago increasing considerably 5,000 years ago.  2,000 years ago 50 million people were living in China  Circulation Models support this idea indicating that a new glaciation would already be underway.

43 Critiques of the Early Anthropogenic Hypothesis  Argue that there were not enough humans to effect greenhouse gases in a substantial way.  Anomaly can not be accounted for even if all the forests in Southern Eurasia were cut down centuries before.

44 Chapter Highlights What are the 5 distinctive developments of humans? What issue does the effect of aliasing raise? Where was the first evidence of agriculture found? What was the main contributing factor to the abnormal high precipitation during the height of the classic Mayan period? What is the general idea of Early Anthropogenic Hypothesis?

45 What were the two hypothesis for the extinction of the megafauna? Evidence points more toward the support of the Savanna hypothesis rather than the Variability selection hypothesis. What is the main difference between the Savanna Hypothesis and the Variability Selection Hypothesis? Chapter Highlights

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