Transcript Just how integrated is the Earth System

The Earth System
Connections among the great spheres
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 !
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
Four Spheres Within Closed System
Within this closed system are
four major, interlinked
components:
Geosphere
Hydrosphere
Atmosphere
Biosphere
Energy and matter are
exchanged between these
components.
In this course, our focus will be
on the biosphere.
So while we’re thinking about
it…
…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.
Earth’s Four Spheres
Geosphere
Geosphere: The solid, inorganic Earth, including Earth’s
surface and layers of its interior.
The Earth is
composed of
nested shells
that are
classified
according to
their chemical
and mechanical
characteristics.
Earth’s Layers: Composition and Mechanical Characteristics
Primarily silica
plus light
metallic
elements
Primarily
silica plus
iron and
magnesium
Primarily iron
and nickel
Composition
crust
Mechanical Characteristics
lithosphere
brittle solid
asthenosphere
solid (but
nearly
liquid)
mantle
mesosphere
solid
outer core
liquid
inner core
solid
core
Geosphere: Chemical and Mechanical
Characteristics Combined
Note: Lithosphere contains both crust and uppermost (brittle) layer of mantle
Some important roles of the geosphere:
1. Contributor of particulate matter (e.g. volcanic ash) to
atmosphere.
2. Ultimate contributor of salts to the ocean (due to ions
being released from weathered rock).
3. Ultimate source of nutrients for all living things.
4. Important contributor of atmospheric gases (from
volcanoes)
5. Movement of plates produces barriers that aid in the
isolation of population of organisms (and therefore
influences evolution).
The Dynamic Geosphere
Processes that occur beneath Earth’s 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.
Earthquakes
Volcanoes
Plate Boundaries
Hydrosphere
Hydrosphere:The hydrosphere is composed of all of the
water in the Earth system, including water in the
oceans, rivers, lakes, air, and below Earth’s 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
Earth’s surface as groundwater).
Surface temperatures of
oceans
(blue= coldest red=
warmest)
The presence of liquid surface water
makes our planet unique.
Hydrosphere
Some important roles of the hydrosphere:
1. Moderates climate
2. Transfers heat
3. Organisms need water to transport nutrients and
waste
4. Water is essential in many of Earth’s processes,
from mineral formation to the weathering and
erosion of rock.
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 won’t get into this
right now)
Some important roles of the atmosphere:
1. Contains the gases that living things need for
survival (e.g., carbon dioxide for photosynthesis,
and oxygen for aerobic respiration).
2. Transfers heat.
3. Ozone in stratosphere protects living things from
excess ultraviolet radiation.
4. Plays a part in weathering and erosion.
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 Earth’s 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.
But…life can thrive in the most unlikely places, from hot
springs to ice caps.
Some important roles of the biosphere:
1. Aids in weathering (e.g. formation of acids in
soil).
2. An important sink for certain elements
(especially carbon).
3. Mediates the formation of some minerals.
4. Photosynthesis maintains the oxygen content of
the atmosphere.
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
Interconnectedness of Spheres
To appreciate how strongly interconnected the Earth’s
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.
Other Circumstances: Earth’s 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 Sun’s energy.
This gives us seasons.
Considering Interactions Between the Spheres
Example 1
Identify some interactions that are represented in this picture
Example 2
What about this picture ?
Example 3
…or this one ?
Small-scale example: A forest fire
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.
Atmosphere: 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.
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.
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.
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).
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.
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).
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:
1.
2.
3.
4.
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.
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…"
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.
Gaia Hypothesis
Put another way, we might view Earth’s 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.
The Biosphere and Gaia
The Gaia Hypothesis is particularly relevant in today’s
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 don’t
know how it works ?
The Bottom Line
Also, to have any hope in realistically reconstructing
events in the past, we must be mindful of the intricate
interconnections between Earth’s components today
(uniformitarianism)
Everything that happens in the biosphere is dependent
on what is happening in the geosphere, hydrosphere,
and atmosphere.
END OF LECTURE