The Earth System

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The Earth System Connections among the great
spheres
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Our Home Planet
About 4.5 billion years old
Only planet presently known to support life
Has well-defined continents and ocean basins
Very dynamic, both internally and externally
A closed system !
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Earth As A Closed System
Mass conserved within system (no gain or loss)
Closed system exchange of energy but negligible
exchange of mass with surroundings
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Four Spheres Within Closed System
Within this closed system are four major,
interlinked components Geosphere Hydrosphere Atm
osphere Biosphere Energy and matter are
exchanged between these components. In this
course, our focus will be on the biosphere. So
while were thinking about it
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Why can Earth sustain life ?

• Not too close or far from Sun, thus preventing
  life from freezing or frying
• Large enough to hold atmosphere
• Abundance of water
• Temperature range to allow water to exist in
  liquid (very important) as well as gaseous, and
  solid forms.
• The interaction of the four components or
  spheres of the Earth system.
• The origin of life is a separate issue, which we
  will discuss later.

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Earths Four Spheres
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Geosphere
Geosphere The solid, inorganic Earth, including
Earths surface and layers of its interior.
The Earth is composed of nested shells that are
classified according to their chemical and
mechanical characteristics.
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Earths Layers Composition and Mechanical
Characteristics
Composition
Mechanical Characteristics
crust
Primarily silica plus light metallic elements
lithosphere
brittle solid
asthenosphere
solid (but nearly liquid)
mantle
Primarily silica plus iron and magnesium
solid
mesosphere
outer core
liquid
core
Primarily iron and nickel
inner core
solid
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Geosphere Chemical and Mechanical
Characteristics Combined
Note Lithosphere contains both crust and
uppermost (brittle) layer of mantle
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• Some important roles of the geosphere
• Contributor of particulate matter (e.g. volcanic
  ash) to atmosphere.
• Ultimate contributor of salts to the ocean (due
  to ions being released from weathered rock).
• Ultimate source of nutrients for all living
  things.
• Important contributor of atmospheric gases (from
  volcanoes)
• Movement of plates produces barriers that aid in
  the isolation of population of organisms (and
  therefore influences evolution).

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The Dynamic Geosphere
Processes that occur beneath Earths surface are
manifest in earthquakes and volcanism. These
phenomena are linked to the movement of tectonic
plates that, in turn, is driven by internal Earth
processes.
Volcanoes
Earthquakes
Plate Boundaries
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Hydrosphere
HydrosphereThe hydrosphere is composed of all of
the water in the Earth system, including water in
the oceans, rivers, lakes, air, and below Earths
surface.
97 percent of the earth's water is in the oceans.
The remaining 3 percent is fresh water (mostly
in ice sheets, but also in the air as vapour, and
below Earths surface as groundwater). The
presence of liquid surface water makes our planet
unique.
Surface temperatures of oceans (blue coldest
red warmest)
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Hydrosphere

• Some important roles of the hydrosphere
• Moderates climate
• Transfers heat
• Organisms need water to transport nutrients and
  waste
• Water is essential in many of Earths processes,
  from mineral formation to the weathering and
  erosion of rock.

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Atmosphere
Atmosphere The atmosphere is the body of gases
that surrounds our planet.
Most of our atmosphere is located close to the
earth's surface where it is most dense. The air
of our planet is 79 nitrogen and just under 21
oxygen the small amount remaining is composed of
carbon dioxide and other gases.
Also has a layered structure (but we wont get
into this right now)
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• Some important roles of the atmosphere
• Contains the gases that living things need for
  survival (e.g., carbon dioxide for
  photosynthesis, and oxygen for aerobic
  respiration).
• Transfers heat.
• Ozone in stratosphere protects living things from
  excess ultraviolet radiation.
• Plays a part in weathering and erosion.

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Biosphere
Biosphere The sphere that includes all living
organisms. Plants, animals, and microbes are all
part of the biosphere. It also includes organic
matter not yet decomposed.
Most of Earths life is found from about 3
metres below the ground to 30 meters above it and
in the top 200 metres of the oceans and seas.
Butlife can thrive in the most unlikely places,
from hot springs to ice caps.
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• Some important roles of the biosphere
• Aids in weathering (e.g. formation of acids in
  soil).
• An important sink for certain elements
  (especially carbon).
• Mediates the formation of some minerals.
• Photosynthesis maintains the oxygen content of
  the atmosphere.

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A Recent Addition to Biosphere Human Activity
The presence of humans and the extent of human
influence can be appreciated by looking at
satellite photos. Even at night, evidence of
human activity can be seen.
White dots major centres of human
population Yellow patches fires from
slash-and-burn farming Red patches natural gas
burning in major oil fields
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Interconnectedness of Spheres
To appreciate how strongly interconnected the
Earths spheres really are, we need only to think
about what happens to substances within the
system. For example, the carbon cycle.
Note that at any given point in time, carbon
occurs in all of the great spheres.
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Other Circumstances Earths Spin and Tilt
Earth is not just a static lump of rock !
As it spins on its tilted axis, it different
areas of Earth are exposed to different
amounts/intensities of the Suns energy.
This gives us seasons.
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Considering Interactions Between the Spheres
Example 1
Identify some interactions that are represented
in this picture
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Example 2
What about this picture ?
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Example 3
or this one ?
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Small-scale example A forest fire
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Interactions Between Spheres Cause and Effect
Initial Conditions Geosphere The ground could
have been very permeable, preventing moisture
from being retained in the upper part of the soil
profile. Hydrosphere The area could have been
prone to fire due to lack of precipitation. Atmos
phere The fire could have started due to a
lightning strike. Biosphere Dead wood, leaves
and needles may have enhanced the ability of the
fire to start and spread.
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Relevance to Geosphere

1. Heat from the fire causes rocks to crack
   (therefore enhancing weathering).
2. Soil erosion is also enhanced by the removal of
   vegetation.
3. Ash particles from the fire alter the chemistry
   of the soil.

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Relevance to Atmosphere

1. Smoke and ash particles are carried by wind to
   other areas.
2. Increased precipitation elsewhere is enhanced due
   to the ash particles acting as nucleation centres
   for water droplets.
3. Gaseous pollutants such as carbon dioxide (CO2)
   are produced during the burning of the vegetation
   and carried into the air by the wind.

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Relevance to Hydrosphere

• Heat from the fire further removes moisture from
  the air, soil, and vegetation through the process
  of evaporation.
• Increased siltation of streams due to enhanced
  erosion (particles are then deposited as
  sediment).

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Relevance to Biosphere

1. Immediate destruction of habitat in burn area.
2. Smoke in the air may have coats the lungs of
   animals, including people, and affects their
   ability to breathe.
3. Ash particles in water clogs the gills of fish
   and other aquatic organisms.

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Relevance to Biosphere
4. On the positive side, nutrients released from
ash from the fire can, on the long term, benefit
future plant communities. 5. Also, seeds of
some plants may require that their outer shells
be burned before they can germinate (so the
forest fire benefits these plants).
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Global Effects

• These types of interactions not only apply to
  local scenarios, but also influence changes on
  global scale.
• Examples of events that may have something to do
  with interactions between components of the Earth
  system
• Initiation of ice ages
• Mass extinctions
• Global climate change
• El Nino events.
• We will look at some of these things in detail as
  the course progresses.

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Just how integrated is the Earth System ? James
Lovelock (1979) introduced a somewhat extreme
concept called the Gaia Hypothesis.
Named after Gaia, Greek goddess of Earth (Mother
Earth) An interesting piece of trivia Gaia was
gentle, feminine and nurturing, but also
ruthlessly cruel to any who crossed her.
Lovelock claims that life, or the biosphere,
regulates or maintains the climate and the
atmospheric composition at an optimum for
itself"
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Is Earth Alive ?
The Gaia concept views Earth as a superorganism.
Inherent in this explanation is the idea that
biosphere, the atmosphere, the lithosphere and
the hydrosphere are in some kind of balance -
that they maintain a homeostatic condition.
This also implies that Earth is somehow aware
of the adjustments needed in its system to
maintain a state of balance that Earth is a
living, breathing, and thinking, entity.
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Gaia Hypothesis
Put another way, we might view Earths processes
as being analogous to how physiological processes
within the human body ensure that temperature,
blood pH, electrochemistry, etc. are kept in
balance for our survival. Few scientists accept
the concept of Earth as a sentient
entity. However, this idea has greatly influenced
the way scientists think about how Earth behaves,
in that it emphasized that every change that
occurs in one part of the Earth system has the
potential to affect all others.
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The Biosphere and Gaia
The Gaia Hypothesis is particularly relevant in
todays world- we are getting increasingly
worried about how our activities are affecting
the Earth.
After all, how can we expect to fix something if
we dont know how it works ?
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The Bottom Line
Also, to have any hope in realistically
reconstructing events in the past, we must be
mindful of the intricate interconnections between
Earths components today (uniformitarianism) Ever
ything that happens in the biosphere is dependent
on what is happening in the geosphere,
hydrosphere, and atmosphere.
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END OF LECTURE