Geography 1001:
Climate & Vegetation
Instructor: Andrés Holz
Teaching Assistant:
Eungul Lee
Agenda for Lecture 13: Monday
July 2
• Today’s lecture:
– Historical development of
the ecosphere
• Biological processes that
changed the atmosphere
• Atmospheric changes
– A bit of ourselves
• How we have modified our
environment at various scales
• Traditional (& less traditional)
modifications of our environment at
local (& global) scales
Agenda for Lecture 13: Monday
July 2
• Today’s lecture:
– A bit of ourselves
• World Population Prospects
• Population collapse predictions
• Could these changes be relevant for
our future?
• Does earth experience natural
changes?
• If so, then what? Take-home
message
A bit of history here…
500 million years ago..
400 million years ago..
300 million years ago..
200 million years ago..
100 million years ago..
50 million years ago..
1 million year ago..
Less than a million year ago..
•So far, we know that the Earth has experienced at least 8 ice ages
•Last one?
Today
•If we think of the earth life being a calendar year (i.e. from Jan 1 to Dec 31),
when do you think we appeared?
But how have the conditions for life
changed over these 4 billion years?
The solar system form
4.6 billion years ago.
4 billion years ago, the
atmosphere was
made off of volcanic
emissions
• TIME
– 4 billion yrs ago
• PROCESS
–
–
–
–
Water vapor
Ammonia (NH3)
Methane (CH4)
Hydrogen sulfide
(H2S)
– Hydrogen gas (H2)
– Carbon monoxide
(CO)
– **Very little O2 & N2
All water was held in the atmosphere as vapor
because of high temperatures (water vapor in
high clouds greenhouse effect).
• TIME
– 4 billion yrs ago
– 3.1-3.5 billion yrs ago
• PROCESS
– Water vapor, CO, (N)
dominant.
– O2 begins to accumulate.
How?
– Water vapor clouds common
in the lower atmosphere
(albedo forcing clouds).
– Cooling of the atmosphere
causes precipitation and the
development of the oceans.
– Break of H2O by ultraviolet
rays H2O  O2 + H
– First single cell algae
& bacteria
• TIME
• PROCESS
– 3.1-3.5 billion yrs ago
– Anaerobic respiration
• Single cells algae were able to
– produce Energy without O2
– Take C-H20 (simple organic molecules
food) &
break down into
CO2 + alcohols
energy
For ~800 millions of years, CO2 was released (as by-products of respiration) &
built up in the atmosphere and oceans
There was enough CO2 in the atmosphere to sustain life….
• PROCESS
• TIME
– Photosynthesis
Single-cells (bluegreen algae have
chlorophyll)
– 2.3 billion yrs ago….
sunlight
CO2 + H2O
CH2O + O2
energy
–Initially, the released O2 was lethal
to the living organisms
food
built up
• TIME
– 1.9 billion yrs ago….
• PROCESS
– Ozone (O3) layer is
being built in the
stratosphere
Filters out the UV radiation making life
possible on land development of O2
tolerant organisms
Aerobic life on the land took longer to start
because it could only occurred after the
ozone layer was formed
• TIME
– 1.3 billion yrs ago….
CH2O + O2
• PROCESS
– Aerobic respiration
CO2 + H2O
energy
• TIME
– 600 mill yrs ago….
• PROCESS
– Life is widespread
in the oceans
• Single cells
• Early fishes
• Large algae
• TIME
– 420 mill yrs ago….
• PROCESS
– Life is widespread
on lands
• Earliest plants
• Invertebrates
• Vertebrates
• TIME
– 350 mill yrs ago….
• PROCESS
– Development of
tropical rainforest
• fossil fuel  today’s
oil
• TIME
– 200 mill yrs ago….
• PROCESS
– Colonization of larger
vertebrates
One of those (smaller) vertebrates
were our ancestors:
a bit of ourselves..
Date of Separation according to
Mitochondrial DNA
Early Human Phylogeny
Africa
Asia
Asia
Europe
eastern Africa
Africa?
southern Africa
eastern Africa
Europe &
W Asia
How we have modified our
environment at various scales
(remember the movie?)
Broad Expansion of Human Habitat
(we took over spatially!)
Remember that 18,000 BP, the Earth looked like
this map from Earth and Life Through Time
Food Web-Land Animals (we also took over new niches)
World Population Trend from
10,000 B.C. to 200 A.D.
Traditional modification of our
environment at local scale
(Less) Traditional modification of
our environment at global scale
• http://www.mongabay.com/deforestation_r
ate.htm
UN, World Population Prospects:1992
A this rate, it was predicted that it would take only 774 years (for the 1994 population of
5.6 billion) to increase to the point where there were 10 human beings for each square
meter of ice free land on the planet!
• Is there any problem with that?
Population collapse predictions
• Malthus (~1800)
– population would
outrun food supply by
1930s
• Technology & Market
economy
Yet, Malthus (& his opponent) didn’t
see the current
• Biodiversity loss
–
–
–
–
Habitat fragmentation
Species introduction (that are taking new niches)
Over hunting
Greenhouse gases
• Could these changes be relevant for our future?
• Does earth experience natural changes?
1-Let’s play with history: First
civilization self-collapse..(local scale)
• Eastern Island
• Mayas Empire
Does earth experience natural changes?
Yes!
Examples:
– Sunspots (~11 cycle)
– El Niño/ La Niña
– Hugh Volcanic
eruptions (random)
– Meteorite impacts
(very infrequent &
very random)
– Ice ages (~100,000
yrs cycle)
– Massive Biodiversity
loss
If so, then what?
Take-home message
• Current rates and scales of these changes
are unprecedented on earth
• Natural changes increasingly influenced
by “we”, may rapidly create new conditions
at the planet scale
– triggering erratic jumps that are hard to
predict and understand
– enhancing feedback loops that weaken these
prediction efforts even further
If so, then what?
Evidence of Ice ages?
• Swiss hunter in the Alps (1815) associated
scratch marks on rocks with the P of ice
Yosemite
Cycles of Ice ages:
Milanković cycles (Theory)
Performed detailed calculations concerning the
periodicity of the earth’s orbital parameters
during the 1920-40s
• Precession
• Axial tilt
• Eccentricity
Eccentricity
• During periods of high eccentricity
higher differences between max & min
distance from sun to earth more
potential for extreme (cold & warm)
climate
Orbit eccentricity
Tilt angle (or obliquity)
Tilt angle (or obliquity)
• The greater the angle of the tilt the
greater the potential for extremes in
seasonal climate (especially for polar
regions)
Precession (or wobble)
Precession (or wobble)
• It’s a ‘slowing down’ of the rotation of the
earth tilt of the earth point to various
directions (like the axe of a spinning top)
• What about us?
How do scientists track glaciation?
• Stable-isotopes from
zooplankton (tiny
shells of calcite)
• Come from seawater
• Once dead built up
on the ocean bottom
as layers (~2.5 cm or
1” = 1,000 yrs)
How do scientists track glaciation?
Lighter Oxygen (16O) evaporates easier with water vapor (due to insolation) and
then precipitates as either:
a) rain and returns with rivers and groundwater to oceans seawater
remains the ~same (interglacial) [e.g. now]
Or
b) snow and accumulates and does NOT return to oceans seawater
change rate between 16O & 18O
Comparison between O2 isotope
record & Milanković theory