the earth system connections among the great spheres
TRANSCRIPT
Our Home Planet
A closed system !
Has well-defined continents and ocean basins
Only planet presently known to support life
About 4.5 billion years old
Very dynamic, both internally and externally
Earth As A Closed System
Closed system: exchange of energy but negligible exchange of mass with surroundings
Mass conserved within system(no gain or loss)
Four Spheres Within Closed System
Within this closed system are four major, interlinked components:
GeosphereHydrosphereAtmosphereBiosphere
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.
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.
crust
mantle
core
lithosphereasthenosphere
mesosphere
outer core
inner core
Composition Mechanical Characteristics
liquid
solid
solid
brittle solidsolid (but nearlyliquid)
Earth’s Layers: Composition and Mechanical Characteristics
Primarily ironand nickel
Primarily silica plus iron and magnesium
Primarily silica plus light metallic elements
Note: Lithosphere contains both crust and uppermost (brittle) layer of mantle
Geosphere: Chemical and Mechanical Characteristics Combined
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 Plate BoundariesVolcanoes
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).
The presence of liquid surface water makes our planet unique.
Surface temperatures of oceans(blue= coldest red= warmest)
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.
Hydrosphere
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.
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.
Atmosphere: The atmosphere is the body of gases that surrounds our planet.
Atmosphere
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
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.
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.
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 populationYellow patches: fires from slash-and-burn farmingRed 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
Identify some interactions that are represented in this picture
Example 1
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.
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).
Relevance to Biosphere
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. Initiation of ice ages2. Mass extinctions3. Global climate change4. El Nino events.
We will look at some of these things in detail as the course progresses.
Global Effects
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…"
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.
Is Earth Alive ?
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.
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.
Gaia Hypothesis
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 ?
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.
The Bottom Line