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Chapter 2 – Earth as a System
Chapter 2. 1 - Earth Basics
Earth is the third planet from the sun in our solar system.
Earth formed about 4.6 billion years ago and is made mostly of rock.
Approximately 70% of the surface is covered with water.
Earth is an oblate sphere, or a slightly flattened sphere.
Earth’s pole-to-pole circumference is 24,804 miles. Its equatorial circumference is 24,845 miles.
Earth’s average diameter is 7,908 miles.
Water
Water is an essential part of the earth system.
Water covers approximately 70% of the Earth’s surface.
It is also the only know substance that exist in all three phases (gas, liquid and solid) on Earth.
Our weight is about 0.3% less at the equator than at the North Pole.
This is because the distance between Earth’s surface and its core is greater at the equator than at the poles.
Weight and Mass
Weight is the measure of the strength of the pull of gravity on an object.
An Object’s weight depends on its mass and its distance from Earth’s Center
Earth’s Energy Budget
Earth has four main spheres.
(1) Geosphere (Rock)
(2) Hydrosphere (Ocean)
(3) Biosphere (Life)
(4) Atmosphere (Air)
These four spheres are open systems that can be thought of as huge storehouses of energy and matter.
Earth’s Energy Budget
Matter and energy are constantly being exchanged between the spheres.
This open system of constant exchange happens through:
(1) Chemical reactions
(2) Radioactive decay
(3) Radiation of energy (light and heat)
(4) The growth and decay of organisms.
Earth’s Interior
Scientists have made important discoveries about Earth’s interior through studies of seismic waves.
Seismic waves are propagating vibrations that carry energy from the source of the shaking outward in all
directions (Pond/rock).
By studying the way seismic waves travel through Earth, scientists have determined that Earth is made up of:
Three major compositional zones and Five major structural zones.
The Three Compositional Zones of Earth’s Interior
1. Crust
The crust is the thin and solid outermost layer of Earth that lies above the mantle
Oceanic crust, which lies under the oceans, is about 5 to 10 miles thick. The continental crust varies in
thickness from 10 to 50 miles.
2. Mantle
The mantle is the layer of rock that lies between Earth’s crust and core.
The mantle is nearly 1800 miles thick and makes up almost half of the Earth’s core.
3. Core
The other half is occupied by the core.
The center of Earth is a sphere composed mainly of nickel and iron and has a radius of about 2,150 miles.
Deepest Point into Earth
The deepest, SG-#, reached 12,262 meters (40, 230 ft) (7.56 miles) in 1989, and is the deepest hole ever
drilled, and the deepest artificial point on Earth.
With the expected further increases in temperature with increasing depth, drilling to 15,000 m (49,000 ft) would
have meant working at a projected 300oC (570oF)
Chapter 2. 2 - The Earth’s Five Structural Zones
Earths interior structure is about 4,000 miles from the earth’s surface to its center and can be broken down into
five distinct structural zones.
1. Lithosphere
The lithosphere is the outmost layer of Earth, also known as the crust, or the think “shell” of rock that covers
the globe.
The rigid lithosphere is between 6 to 50 miles thick.
2. The Asthenosphere
The “soft” zone below the lithosphere is called the asthenosphere, (Greek for weak) and extends for about 100
miles.
The asthenosphere is responsible for many of the earth’s activities, including earthquakes, certain types of
volcanic activity, and continental drift.
Below the depth, seismic wave velocity increases, suggesting an underlying denser, but solid phase.
3. The Mesosphere
The mesosphere literally, the “middle sphere” and is the more solid phases from the base of the
asthenosphere.
Ranges from 150 miles to the core at 1,800 miles
Within this layer seismic waves sharply increase in speed suggesting compositional changes within the
mesosphere.
4. Outer Core
There is another abrupt change at 1,800 miles often referred to as the core-mantle boundary (CMB).
Seismic S-Waves disappear at the core-mantle boundary (CMB) denoting a phase change from a solid mantle
above to the start of Earth’s liquid outer core.
The phase change is also accompanied by an abrupt temperature increase of 1,300oF
The hot outer core is about 1350 miles in radius and is a liquid mixture of iron and denser than the mantle.
The interaction between the solid mantel and the liquid outer core is very important to Earth’s dynamics.
First it provides the driving force (convection) for plate tectonics.
Second it theorized that the motion and currents in the core's iron-rich fluids are responsible for the earth’s
magnetic field.
Earth as a Magnet
Earth’s magnetic field extends beyond the atmosphere and affects a region of space called the
magnetosphere.
Without the outer core their would be no magnetosphere to protect the Earth from cosmic rays and harmful
ultraviolet radiation.
5. Inner Core
The last transition occurs at 3,150 miles and extend for the final 800 miles
Scientists believe the material below 3,150 miles is solid because seismic P-waves speed up and are reflected.
It is theorized the phase change from liquid to solid is due to the immense pressures present at this depth.
The inner core has a different composition than the outer core.
Inner core is a pure iron-nickel composition.
The outer core consists of a liquid that is 80–92% iron, alloyed with a lighter element like silicon or sulfur.
Chapter 2.3 – Understanding Energy
The operation of the Earth system is a result of interaction between the two most basic components of the
universe: matter and energy.
Matter
Matter is anything that has mass and takes up space (gas, liquid and solid).
Energy
Energy is defined as the ability to do work.
Energy can be transferred in a variety of forms.
The First Law of Thermodynamics
The first law of thermodynamics is often called the Law of Conservation of Energy.
The 1st law states that energy may neither be created nor destroyed
Simply put all of the energy of the universe has to end up somewhere, either in the original form or in a
different form.
Thus, the sum of energy available in the universe is constant.
Example heat:
Whenever heat is added to a system, it transforms to an equal amount of some other form of energy.
There are many different forms of energy, which is a quantitive property (either kinetic or potential).
Einstein E=mc2
One of Einstein's great insights was to realize that matter and energy are really different forms of the same
thing.
Where E is energy, m is mass, and c is the speed of light in a vacuum - E = mc²
Roller Coasted Example
An example of the 1st law of thermodynamics is a rollercoaster.
As you dropped down the tracks all the potential energy that was stored up when you ascended up in the car
turns into kinetic energy.
Second law of thermodynamics
The second law of thermodynamics states that when energy transfer occurs, matter becomes less organized
with time.
Thus, the universe’s energy is spread out more uniformly over time.
As the disorder in the universe increases, the energy is transformed into less usable forms.
Thus, the efficiency of any process will always be less than 100%.
Internal Sources of Energy of Earth
When Earth formed about 4.6 billion years ago, its interior was heated by radioactive decay and gravitational
contraction.
The decay of radioactive atoms still generates enough heat to keep Earth’s interior hot.
By the process of convection, the heat in Earth’s interior is transferred through the layers of Earth and is
released at Earth’s surface.
External Energy Sources
Earth’s most important external energy source is the sun.
Solar radiation warms Earth’s atmosphere and surface.
This heating causes the movement of air masses, which generates winds and ocean currents.
Photosynthesis (chemical reaction) also requires solar energy.
Earth’s Gravity
Gravity is the force of attraction that exists between all matter in the universe.
According to Newton’s law of gravitation, the force of attraction between any two objects depends on the
masses of the objects and the distance between the objects.
The larger the masses of two objects are and the closer together the objects are, the greater the force of
gravity between the objects will be.
Gravity of Moon
Another important external source of energy is gravitational energy from the moon and sun.
This energy helps generate tides that cause currents and drive the mixing of ocean water.
Chapter 2.4 - Earth-System Science
A cycle is a group of processes in which matter and energy repeatedly move through a series of reservoirs.
A reservoir is a place where matter or energy is stored.
Cycles in the Earth Systems
The total amount of matter on Earth does not change.
Earth is referred to as a closed system:
Energy is exchanged but not matter
On Earth the way matter is stored or cycles between reservoirs may change but the amount of matter does
not.
If balance is not kept it can have an affect on the living organisms.
The Carbon Cycle
The carbon cycle is the exchange of carbon among three reservoirs or storage place: the land (lithosphere),
the oceans (hydrosphere), and the atmosphere.
Carbon is a key element for life, composing almost half of the dry mass of the earth’s plants. (water removed).
Of the three, the atmosphere is the smallest pool of actively cycling carbon.
The land and its plants and animals (biosphere) is the next largest reservoir of carbon.
The oceans are the earth’s largest active carbon reservoir by far.
The Carbon Cycle Time Scales
The short-term carbon cycle includes processes that transfer carbon from one reservoir to another in a matter
of years.
Scientists call the slower transfers of carbon among reservoirs the long-term carbon cycle.
Short Term Carbon Cycle Begins
Photosynthesis is the primary process that pulls carbon from our atmosphere in the form of carbon dioxide.
Animals obtain most of their carbon through eating other plants and animals
CO² is released back into the atmosphere by:
(1) respiration of animals
(2) combustion of fossil fuels and forest fires.
(3) the breakdown of dead plants (decomposition).
Globally, photosynthesis and respiration tend to be in balance.
Short-Term Carbon Cycle (Ocean)
The oceans absorb and store more than 60 times as much carbon as the atmosphere.
They also receive carbon from water runoff (rivers).
CO² in the short-term will be used in the shallows by plants and algae that need photosynthesis to live.
The carbonate that forms when CO² dissolves into surface waters will be used by marine animals for their
exoskeleton shell.
Long-Term Carbon Cycle (Ocean)
Unused CO² can also stored for longer periods of time because it is more soluble in cold water.
Unused CO² in the shallows is transferred toward the ocean floor via the deep water current (the conveyor-belt
circulation) creating an ocean sink of carbon.
Long-Term Carbon Cycle Storage
This ocean sink along with the accumulation of dead marine organisms forms the permanent rocks limestone
and dolomite.
The process of dead organisms literally sinking and being compressed into liquid (oil) or solid matter (coal) as
fossil fuels both on land and in the ocean make up the other part of the long-term carbon cycle.
The Carbon Sink (Long-Term Return)
The carbon is returned to the atmosphere in one of two ways
(1) weathering (erosion of rocks - dolemite and limestone)
(2) volcanism
The Global Warming Concern
Fossil fuels are extracted from underground, so they are not a natural part of the short-term cycle.
When fossil fuels are burned, carbon from long-term storage is added to the short-term cycle.
The Carbon Sink (Long-Term)
When this happens:
(1)The greenhouse effect increases because there are more carbon gases in the atmosphere.
(2) The balance of the cycle is also disrupted.
Chapter 2.5- The Water Cycle
The movement of water from the atmosphere to Earth’s surface and back to the atmosphere is called the water
cycle.
Evaporation
In the water cycle, the amount of water on Earth never changes it instead cycles.
Changing from liquid water-to-water vapor through the energy transfers involved in evaporation and
transpiration.
Transpiration
The movement of water from plants to the atmosphere.
Condensation
During these processes, water absorbs heat and changes into a gaseous state through condensation.
Precipitation
When the water loses energy, it cools and condenses to form rain or snow also known as precipitation.
Nitrogen Cycle
Nitrogen (N²) makes up 79% of our atmosphere [oxygen (O²) 21%].
Nitrogen is one of the building blocks of life on this planet.
It is a major components of amino acids and the building blocks of protein (muscle).
In the nitrogen cycle, nitrogen is removed from the atmosphere by biological fixation (bacteria) and
atmospheric fixation (lightning).
Bacteria breaks apart the N² and plants then metabolized the nitrogen via their roots.
Animals get their nitrogen from the food they consume, passing the nitrogen farther and farther up the food
chain.
Nitrogen is returned to the system when animals excrete waste.
Or by decay otherwise called nitrogen mineralization where waste is broken down by bacteria and released
back into the air.
Humans and the Earth System
All natural cycles can be altered by human activities.
The carbon cycle is affected when humans use fossil fuels.
The fertilizers and pesticides used in agriculture can have an adverse effect on the bacteria involved in the
nitrogen cycle.
Humans must be careful to moderate their influences on natural systems
Ecosystems
Ecology is the study of the complex relationships between living things and their nonliving, or abiotic
environment.
Ecosystem a community of organisms and their abiotic environment.
An ecosystem may be as large as an ocean or as small as a rotting log.
Energy flows through an ecosystem starting with solar energy  producers (plants)  consumers.
The Producers
Organisms that make their own food are called producers.
Most producers use energy from the sun to produce their own food.
The Consumers
Consumers are organisms that get their energy by eating other organisms.
Consumers may get energy by eating producers or by eating other consumers.
Decomposers
Some consumers get energy by breaking down dead organisms.
These consumers are called decomposers.
Ecosystem
To remain healthy, an ecosystem (food chain) needs to have a balance.
Catalina Island (1924)- Bison, were brought to film a movie and left there.
The bison population exploded on an island ill-adapted for large animals.