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Transcript
Early Humans and Climate
•Evolution & Extinction – Process of the rise and fall of species
•Important moment in human evolution
•4 mya: First hominids (our distant ancestor)
•200 kya: Homo Sapiens (us) appear
•12 kya: Human become farmers
•200 years ago: Industrial Revolution begins – fossil fuel burning
•Important events in recent climate history
•30 mya: Global cooling begins (Himalayas forming)
•2.75 mya: Enter ongoing Ice Age
•8000 years ago: CO2 deviates from “normal” trend
•6000 years ago: CH4 deviates from “normal” trend
•Are these changes in Humans and Climate related? Almost certainly
and in both directions.
Evolution
• “Remodeling not New Construction”
• Natural Mechanism – Natural Selection
– Survival of the Fittest, but who is the “fittest”?
– Fitness is determined by environmental situation
• Speciation – appearance of a new species
– Species – group of organisms whose member can
interbreed
– Speciation usually caused by isolation of a small
group in a region with different environmental
stresses
The Evolutionary Path to Humans 1
The Evolutionary Path to Humans 2
The Evolutionary Path to Humans 3
The Evolutionary Path to Humans 4
1 HOMO HABILIS ~ NICKNAME: Handyman LIVED: 2.4 to 1.6
mya HABITAT: Tropical Africa DIET: Omnivorous – nuts,
seeds, tubers, fruits, some meat
2 HOMO SAPIEN ~ NICKNAME: Human LIVED: 200,000 years
ago to present HABITAT:All DIET: Omnivorous - meat,
vegetables, tubers, nuts, pizza, sushi
3 HOMO FLORESIENSIS ~ NICKNAME: Hobbit LIVED: 95,000
to 13,000 years ago HABITAT: Flores, Indonesia
(tropical) DIET: Omnivorous - meat included pygmy
stegodon, giant rat
4 HOMO ERECTUS ~ NICKNAME: Erectus LIVED: 1.8 million
years to 100,000 years ago HABITAT: Tropical to temperate Africa, Asia, Europe DIET: Omnivorous - meat, tubers, fruits,
nuts
5 PARANTHROPUS BOISEI ~ NICKNAME: Nutcracker
man LIVED: 2.3 to 1.4 mya HABITAT: Tropical
Africa DIET: Omnivorous - nuts, seeds, leaves, tubers, fruits,
maybe some meat
6 HOMO HEIDELBERGENSIS ~
NICKNAME: Goliath LIVED: 700,000 to 300,000 years
ago HABITAT: Temperate and tropical, Africa and
Europe DIET: Omnivorous - meat, vegetables, tubers, nuts
7 HOMO NEANDERTHALENSIS ~
NICKNAME: Neanderthal LIVED: 250,000 to 30,000 years
ago HABITAT: Europe and Western Asia DIET: Relied heavily
on meat, such as bison, deer and musk ox
The Evolutionary Path to Humans 5
Climate affects on human evolution
Savanna Hypothesis
• Cooling and drying of Africa
started 30 mya
• Forest shrink; by 4 mya this
would reduce habitat for
early humans
• Humans fled to the savanna
– Beginning walking upright,
and free hands for other uses
– Drives evolutionary changes,
like larger brains
Variable Selection Hypothesis
• Early humans have been
around since current Ice Age
started
• Subjected to many
glacial/interglacial cycles
• These numerous changes
“forced” evolutionary changes
• Problems:
– Tropical Africa may have been
little effect by glacial cycles
– Monsoon rains continued in
Africa throughout the changes
in glacial cycles
• Problem – Fossil evidence
shows humans lived in
many environments, not
just savanna
Bottomline – Human fossils are quite rare and tracking such linkages
between human evolution and climate change is very challenging.
Origin of Agriculture
• 12 kya: A group of people stop being nomadic
and learn to farm in the Golden Crescent
• 10 kya: Domesticated animals and grains
produced in China
• What was happening at this time?
– Melting of last major ice sheets
– Monsoons very strong in the Middle East
• Did climate “cause” humans to settle down?
– 1) Monsoons for abundant resources so people did
not have to “chase” their next meal, or look for water
– 2) The Younger Dryas, back to cooler planet, may have
made resources scarce and so people banded
together to help each other survive
Has climate change affected
civilizations? Absolutely
• Egypt – Culture peak about 5000 years ago, with
decreasing monsoons the culture gave way to
others
• Mayans – 250 – 900 AD Yucatan Peninsula; AD
860 civilization came to an abrupt end
– Lake sediments show this as a time of severe drought
• Anasazi – 1300 BC to 1300 AD they flourished
– But disappeared during time of extreme drought
– Or possible, simply over used the available resources
• Area was heavily deforested
Example of Early Human Impact –
Megafauna Extinction
• Large mammals suffered a severe extinction
12,500 years ago.
• Climate change? – just coming out of glacial
period
– But these same mammal species had survived
numerous pervious glacial/interglacial transitions
• In many regions around the world this
extinction appears to coincide with human
arrival
Humans and PreIndustrial Climate
Change: Ruddiman’s Hypothesis
Early Anthropogenic Hypothesis: CO2 and CH4 are not
following the same trend during this interglacial period as
they have in the past. Hypothesis attributes this to human
activities.
Hypothesized Causes of GHG trends in
the current interglacial period
• GHGs peak about 7000 – 8000 years after glacial
maximum (1/4 of precession cycle with influence
from tilt cycle) – about 12 kya
• CO2 – deviated from “normal” trend 8 kya
– Humans deforested much of Europe
– Burning and rotting trees add CO2 to atmosphere
– Fewer trees left to remove CO2 from atmosphere
• CH4 – deviated from “normal” trend 5 – 6 kya
– Natural cause: decreasing monsoons, fewer wetland
– Human cause: irrigation in Asia
Problems with Ruddiman’s Hypothesis
• CO2 rises are too large for the deforestation to account
for
• CH4 rises is at least partly naturally caused by reduced
precession-cycle-driven monsoons
Observation clearly show something different in
occurring this interglacial – and human activity is one
possible explanation
Complex feedback effects in addition to deforestation and
irrigation could be an answer