humans and pre-industrial climate
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Humans and Pre-Industrial Climate. The black curve shows the northern hemisphere temperature in a climate model. . Michelle Letendre, Evan Wise, Chance Snow, Mary James, Sara Smith, Cristy Echaves. Climate and Human Evolution. Humans evolved in Africa. Radiometeric dating . - PowerPoint PPT PresentationTRANSCRIPT
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.
Climate and Human Evolution
Radiometeric dating
Humans evolved in Africa
Evidence of Human Evolution5 Distinctive Developments
Onset of bipedalism
Use of stone tools
Initial branching off from primate ape
Development of large brainsBranching of the pre-human
line into genus Homo
Human ancestors & chimpanzees branched off
Humans evolved from a small shrew-like mammal
Primitive apes evolved
Appearance of Human Ancestors
Molecular Biology
Walking Upright
The development to walk is still argued today
Hominins
Hominidae
4.3 myr ago
3.6 myr ago
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
Appearance of Homo
Ancestral australopithecines
Paranthropus
Homo erectus
Stone tools and use of intellect & imagination = Frequent & vast movement
Brain Size
Hominid Braincases Growth by Volume
Type Age (Myr ago) Braincase (cm3)
Homo sapiens 0.2 – 0 1100 – 1500
Homo erectus 2.4 - 1.8 800 – 1000
Australopithecus 4.1 - 3.1 400 - 500
Braincase – part of the skull that houses the brain
Braincase volume has 3x
Unusually rapid compared to many evolutionary changes
Did Climate Change Drive Human Evolution?
• Savanna Hypothesis• Sediments from Indian and Atlantic Ocean
Support this Hypothesis
Atmospheric CO2
• A long term decrease in atmospheric CO2 could have been a factor in the change in vegetation
• There was a change from C3 to C4 carbon on all continents
Volcanic Plateaus
• Vegetation shifted from forest to grassland
• Cooling of Western Indian Ocean
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.
• 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.
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.
Aliasing
• Different signals become indistinguishable when sampled, or aliases
• Also refers to distortions or artifacts that appear in signal reconstructions
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
Aliasing = Misrepresentation
Specimens may not be representative of the population
Depiction of inaccurate long-term trends
Aliasing = Misrepresentation
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
Volcanic Plateaus
Vegetation shifted from forest to grassland
Cooling of Western Indian Ocean
First Evidence of Agriculture
•Fertile Crescent
oAbandonment hunting/gathering
oDomestication of: cattle, livestock, barley, etc.
•
Association of Deglaciationand Agriculture
Hypothesis about cause and effect link
=
Proposed Cause and Effect Links
• The changing conditions made agriculture more favorable
• The Younger Dryas– Climatic reversal
Early Civilizations and Climate Change
Climate change is hypothesized to be a major contributing factor to the deterioration of
early civilizations
Changing Saharan Monsoons coincided with the movement of peoples throughout the Sahara and the
development of the early Egyptian dynasties.
The Mayan Classic Period 300 AD-1,000 AD
Data Collected from lake beds and stalactites indicate severe drought events during the declining years of the Maya.
Anasazi
Climate Change and the Anasazi
Resource Depletion Coupled with Changing Climate
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?
AustraliaDuring 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
Climate
One of the major explanation of the megafaunal extinction in North America is climate change
The deglaciation caused strong summersScientists have been critical of climate hypothesis because many of the mammals went extinct over
12,500 years ago
Overkill HypothesisThe 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
Criticism of the Overkill HypothesisWere there enough people to cause extinction of the megafauna?
o Large mammals have slow reproductiono 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?
Black Sea Flood Hypothesis
tries to explain the worldwide flood and the widespread
deposit
Diluvial Hypothesis
Early Anthropogenic Hypothesis
States that cyclic variations in CO2 and CH4 driven by Earth’s orbital changes during the 350,000 yrs predict a decrease in CO2 and CH4 but anomalies in the data show an increase in CO2 occurring 8,000 yrs ago as well as a rise in CH4 occurring 5,000 years ago.
Deforestation began 8,000 yrs ago leading to an increase of CO2.Large scale rice cultivation began in India and China 5,000 yrs ago
producing higher levels of CH4.
Proposed byWilliam Ruddiman
CO2 & CH4 Influences
Further Evidence for the Early Anthropogenic Hypothesis
5, 000 years ago the Monsoon weekend across the Sahara reducing CH4 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.
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.
Chapter HighlightsWhat 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?
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