Download Chapter Four

Chapter
Four
systems: a theoretical framework
The Biosphere
…
the biosphere includes air, rocks, water and life
• Atmosphere: a mixture of nitrogen (78%),
oxygen (21%), and carbon dioxide (1%)
• Hydrosphere: the water on Earth in all its
states and the elements dissolved in it
• Lithosphere: the thin crust between the mantle
and the atmosphere (rocks)
• Ecosphere: made up of all living organisms;
temporary accumulators and sources of
pollutants
Types of
Systems:
• Open System: exchanges matter and energy with its
surroundings
• Closed System: exchanges energy but not matter with its
environment
• Isolated System: exchanges neither matter nor energy with
its environment
Closed System:
• Closed systems are very rare on earth; the earth
itself can be almost considered a closed system
Open System:
• Most systems are open systems; all ecosystems
are open
Isolated
System
• Isolated systems do not exist naturally, yet it is
possible to picture the entire universe as an
isolated system
Laws of
Thermodynamics
• First Law:
– “energy is neither created nor destroyed”
• Second Law:
– “the entropy of an isolated system not in equilibrium
will tend to increase over time”
•Energy conversions are never 100% efficient
Entropy: the spreading out or dispersal of energy
Equilibrium:
• Steady-State Equilibrium: a characteristic of open systems
where there are continuous inputs and outputs of energy and
matter, but the system as a whole remains more-or-less
constant
• Static Equilibrium: there is no change over time; when
disturbed, it will adopt a new equilibrium
*** Systems can also be stable or unstable
Feedback
• Positive Feedback 
– When students respond positively to teaching methods
through learning and showing interest
• Negative Feedback 
– When students respond negatively to teaching methods
through distraction, indifference or dissent
Positive Feedback
in Global Warming
Higher Temperature
More Heat Trapped
By Atmosphere
Wetter Atmosphere
Land and Sea
Temperatures Rise
Increased Evaporation
More Water Vapor
Transfers and
Transformations
•Transfer: Occurs when the flow does not
involve a change of form or state
•Transformation: Occurs when a flow does
involve a change of form or state
Transfers and
Transformations
Transfers
Transformations
Movement of material through
living organisms
Movement of material in a
non-living process
Movement of energy
Matter to matter
Energy to energy
Energy to matter
Flows and
Storages
“Both energy and matter flow (as inputs and outputs) through
ecosystems but, at times, they are also stored (as storage or stock) within
the ecosystem”
• When one organism eats another, the energy is flowed
between them as stored chemical energy
• Energy flows through a system in the form of carboncarbon bonds within organic compounds
• Matter cycles around the system as minerals
General Flows in
An Ecosystem
Atmosphere
Weathering
Rock cycle
Elements
locked in
sinks
Respiration
Feeding
Sedimentation
and
Fossilization
Elements
combines in
plant tissue
Elements
combined in
animal tissue
Volatile Gases
Death and
Decomposition
Absorbed
Nutrient
elements in
soil and water
Energy Flow and Flow
of Matter Through
an Ecosystem
heat
heat
Producers
Consumers
Inorganic
Nutrient
Pool
Decomposers
SUN
heat
Complexity
and Stability
• Most ecosystems are very complex systems that
include feedback links, flows, and storages
• Primarily, a high level of complexity makes for a
more efficient and stable system
– i.e. tundra ecosystems are quite simple therefore
populations within this ecosystem tend to fluctuate such
as the lemming population (unstable)
Models of
Systems
“Simplified models of systems can help predict changes
in the system by modeling reality...”
A model can take many forms:
• A physical model (i.e. an aquarium)
• A software model (i.e. of climate change)
• Mathematical equations
• Data flow diagrams
Gaia
• Alfred Russel Wallace described the
atmosphere as the “Great Aerial Ocean”
• In 1979, James Lovelock published his
“Gaia hypothesis” in Gaia: A new look of
life on Earth
– Argued that “the Earth is a planet-sized
organism and the atmosphere is its organ
that regulates it and connects all its parts”
– Argued that “the biosphere keeps the
composition of the atmosphere within
certain boundaries by negative feedback
mechanisms”
Lovelock’s
Argument Was Based
On…
1. The temperature of the Earth’s surface is constant
2.
3.
even though the sun is giving out 30% more energy
than when the Earth was formed
The composition of the atmosphere is constant with
79% nitrogen, 21% oxygen, & 0.03% carbon
dioxide. Oxygen is a reactive gas, but its proportion
does not change
The oceans’ salinity is constant at about 3.4% but
rivers washing salts into the sea might be expected to
increase this
Lovelock’s Work
• Although many people rejected his hypothesis
Lovelock defended it for 30 years with the
support of Lynn Margulis
• He developed “Daisyworld” as a mathematical
simulation that depicted how feedback
mechanisms can evolve from activities of selfinterested organisms
James Lovelock
• In 2006, Lovelock wrote The
Revenge of Gaia, in which he
argues that Earth is an “older
woman”, more than half-way
through her existence as a
planet and not as able to
bounce back like before
• He says that we will be entering
a stage of positive feedback
where the stable equilibrium
will become unstable and thus
result in the shift to a new and
hotter equilibrium state
– “The human population will
survive but with a 90% reduction
in numbers”
The End!