Download Carrying Capacity

Chapter 1 Objectives
• This is the introductory chapter. After reading this chapter you
should be able to:
• 1. Identify the four spheres of Earth
• 2. Describe the composition of each sphere.
• 3. List forms of interaction between spheres.
• 4. Define a system
• 5. Describe the types and rates of changes.
• 6. Describe the scientific method.
• 7. Explain the importance of geologic time.
Our Solar System
Our Solar System
evolved about 4.6
billion years ago from
a cloud of dust and
gas that rotated in
space and eventually
coalesced into the
Sun, the planets and
their moons under the
pull of gravity. Yet
today, all of the
planets are different.
Lets compare Venus,
Mars and Earth.
Venus
Is it hospitable? It most resembles Earth in size, density
and distance from the Sun, but atmosphere is rich in
carbon dioxide and caustic sulfuric clouds fill the sky.
Lead would melt at the surface…why so different then
Earth?
Fig. 1-1, p.3
Mars
Evidence of water. Its surface has similar features as
Earth (water features such as extinct canyons, stream
channels, lake beds). At one time this planet may have
had flowing water; but today, it is frigid and dry with ice
caps of frozen carbon dioxide.
Fig. 1-2, p.3
If these planets formed at the same time, why are they so different
today? The original atmospheres of Earth, Venus and Mars evolved
into swirling mixtures of carbon dioxide and carbon monoxide, water,
ammonia, methane and other gases. Consider how H2O and CO2 exist
on Earth.
•
Venus: closer to the Sun, water never condensed, CO2 remained in the
atmosphere (no seas to dissolve in). These greenhouse gases (H20, CO2)
would have what effect?
•
Earth cool enough for water vapor to condense, form oceans and dissolve CO2
from the atmosphere…so large quantities of greenhouse gases removed from
the atmosphere and it cooled at a temperature favorable for liquid water and
life. Our initial atmosphere replaced by an atmosphere rich in nitrogen and
oxygen. Where did the oxygen come from?
*
Mars a little farther from the Sun than Earth, less solar radiation. Initially rain
fell, rivers flowed, and lakes/oceans formed (possibly life formed). But
distance from Sun lowered greenhouse gases in atmosphere. Temperatures
dropped (commonly below freezing to as low as -140 degrees C or -220
degrees F).
The Earth’s four spheres
• Planetary changes are driven by complex
interactions among the “spheres”…
• On Earth, what are they?
• Which one is largest? (see page 5).
1.2 The Earth’s four spheres
• Geosphere - the solid earth
– Planets accreted from dust
into planetesimals
– Planetesimals clumped
together to form planets
– Colliding pieces (and
radioactivity) created heat,
warming the young Earth to
melting and differentiation
into layers
– This ended (or Earth started)
about 4.6 billion years ago
The Earth’s Layers: Core, Mantle and Crust
• Metallic core: Fe and
Ni, temp hot as Sun’s
surface (6000 degrees
C), inner core is solid,
outer core is liquid.
• Less-dense rocky
mantle: Changes with
depth, some parts solid,
others weak and
plastic-like, flowing
slowly.
• Least-dense crust:
crustal material varies
widely.
Fig. 1-4, p.6
Granitic Rock of Baffin Island, Canada
(common rock of the continental crust formed from magma)
Fig. 1-5a, p.6
Sandstone and Limestone of the desert in Utah, USA
(how do these types of rock form?)
Fig. 1-5b, p.6
• Lithosphere – the crust and upper part of
mantle
– Average 100km thick
– Broken up into tectonic plates
– Plates float atop the weaker material
– 7 major (and several minor) plates are in
constant motion
The Earth’s Interior
• A slice through the Earth. According to Plate Tectonics
Theory, the lithosphere is broken into segments called
tectonic plates. They move on the asthenosphere at
about the rate your fingernail grows. This movement
accounts for earthquakes, volcanoes, other phenomena.
Fig. 1-6, p.7
Hydrosphere
All of Earth’s water
• Oceans not only contain
97.5% of Earth’s water, but
cover 71% of the Earth’s
surface.
• Glaciers cover 10% of the
Earth’s surface and contain
about 1.8% of its water.
• Only 0.01% is water at
Earth’s surface (streams,
lakes), 0.63% is underground
and 0.001% is in the
atmosphere
Fig. 1-7, p.7
• Atmosphere
• Mixture of gases,
mostly nitrogen and
oxygen.
• Held by what force?
• Mostly concentrated
(99%) in the first 30 km
above Earth.
• Supports life, acts as a
filter (shield) and
blanket. Transport heat
around the globe.
Fig. 1-8, p.8
Biosphere
• Zone inhabited by life.
• Includes the uppermost geosphere, hydrosphere
and lower atmosphere.
• Plants and animals not only depend on the
Earth’s environment, but alter and form the
environment they live in.
Earth Systems
• System: assemblage or combination of interacting
components that form a complex whole.
• Systems are driven by flow of energy and matter. Large
systems are composed of many smaller ones…the
human body for example…and human’s interact in
ecosystems, which interact with other Earth systems!
• Earth’s major systems are its spheres, subdivided into
many interacting smaller ones. Discuss a volcanic
eruption?
• What are Earth’s systems powered by??
• Several energy and material cycles are important in our
study of Earth’s systems…what is one of these? All
spheres continuously exchange matter and energy.
Earth’s materials and processes are part of one
integrated system…
• The Carbon Cycle: All of Earth’s cycles and spheres are
interconnected. For example, the formation and decomposition
of limestone is part of the rock cycle because limestone is a
rock. The same process is also part of the carbon cycle
because limestone is composed partly of carbon.
Fig. 1-9, p.10
• Earth’s cycles
and spheres are
interconnected.
Fig. 1-10, p.11
Time and Earth Science
• James Hutton, 1700s. Regarded by many as
the “Father of Geology”. Observed how
sandstone formed, deduced the Earth must be
very old.
• He formulated “uniformitarianism” (gradualism):
geologic change occurs over long periods of
time, by a sequence of almost imperceptible
events (erosion, plate motions).
• “The present is the key to the past” (explain
geologic events of the past by observing
changes today).
• Not all change is gradual: “Catastrophism”
occurs, this idea was put forth by geologist
William Whewell (floods, earthquakes).
• Hutton
observed
that a
sandstone
outcrop,
like this
one in
Utah, is
composed
of tiny
round sand
grains
cemented
together.
Fig. 1-11, p.12
Today we
know from
age dating
rocks and
other
methods
that the
Earth is
about 4.6
billion
years old.
Fig. 1-12, p.13
-Most geologic change is gradual. Movement of tectonic plates
is slow, yet accounts for mountains, volcanic eruptions,
earthquakes and other geologic phenomena.
-Catastrophic events have occurred throughout the 4.6 billion
years of Earth’s history. 50,000 years ago, a meteorite crashed
into the Arizona desert, creating meteor crater. Larger impacts
may have caused mass extinctions (possibly killing the
dinosaurs off 65 million years ago).
Fig. 1-13, p.14
1.5 Threshold and feedback
effects
• Threshold effect – slow or no initial change to
environmental change
– When threshold point is passed, change becomes rapid
(for example, melting of glaciers).
• Feedback mechanism
– one change affects another system component,
amplifying original effect…can be positive or
negative.
• Today there are
approx. 6.5 billion
people on Earth.
• 40% of land area
is developed.
• Species extinction
rate is high.
• CO2 is at a high
level (Earth’s temp
raised .6 degree C
since Industrial
revolution).
• Do we have
enough
resources?
• Will our growth
trigger climate
changes? …
Fig. 1-14, p.15
• Current trends
– Population is
increasing, but slower
(7-14 billion estimated
when stable)
– India/China becoming
richer – richer people
consume more
resources
– Population and
consumption continue
to rise with serious
environmental
consequence (see
Table 1.1)
Fig. 1-16, p.18
Carrying Capacity
• How many people can Earth support?
– Calculations of carrying capacity vary considerably
– Increasing amounts of food can be produced
– People can migrate from areas of famine or poverty to
less crowded or wealthier areas
– BUT Earth’s
resources are
finite, so
solutions are
temporary
Carrying Capacity
• Example of Rapa Nui (Easter Island)
– Isolated Pacific island with poor soil and little
water
– Settled by 25-50 Polynesians in 5th century
• Survived easily on chickens and
yams, plenty of free time
• Developed elaborate competition
between clans with moai
(statues)
– Civilization peaked at 1550,
with population of ~7000
Carrying Capacity
• Example of Rapa Nui (Easter Island)
– Reached by a Dutch ship in 1722
• Found about 2,000 people living in caves
• Primitive society, constant warfare
– Rapa Nui’s carrying capacity had been
drastically lowered by society’s actions:
• Transportation of moai had required cutting down
trees
• Erosion of soil made yams scarce
• Lack of canoes made fishing difficult and escape
impossible
The Scientific Method (see page 15)
• Observation, Hypothesis, Theory and Law.
• Observation: starting point of science. Collect facts.
• Hypothesis: tentative explanation built on strong
supporting evidence. Tested by comparison, additional
observations and experiments.
• Theory: If hypothesis explains new observations and is
not substantively contradicted, can become a theory.
Should be supported and explain many observations
without major inconsistencies (theory of plate tectonics).
• Law: statement of how events always occur under given
conditions. Considered factual and correct (law of
gravity). Very few laws.
Fig. 1-15, p.16