10/16/00
GEOS 2004
Mid-term Examination
1. The three inanimate components of the Earth System are the geosphere, the hydrosphere and the atmosphere. The geosphere is the solid part of the earth, and is comprised of the core, mantle and crust. The core of the earth is divided into the outer core and the inner core. The outer core consists mostly of liquid nickel and iron, but has traces of a few other elements as well. Earth’s magnetic field is produced and maintained by motion in the outer core that transfers heat. The outer core begins at approximately 2900 kilometers beneath the surface, and ends around 5200 kilometers beneath the surface. The inner core is made up of mostly crystallized nickel and iron, begins at approximately 5200 kilometers beneath the earth’s surface, and ends at about 6400 kilometers beneath the earth’s surface. The mantle is divided into two layers: the upper mantle and the lower mantle. The upper mantle ranges from approximately 40 kilometers beneath the earth’s surface to about 700 kilometers beneath the earth’s surface. It is divided into the lower lithosphere, asthenosphere and the transition zone. Most of the upper mantle consists of iron and magnesium silicates, but also contains some calcium and aluminum. The lower mantle ranges from approximately 700 kilometers beneath the earth’s surface to about 2900 kilometers beneath the earth’s surface. It is comprised of mostly silicon, magnesium and oxygen, but also has traces of iron, calcium and aluminum. The crust is a relatively thin layer of rock that forms the solid outer shell of the geosphere. Its average thickness is about 40 kilometers. The earth’s crust is significantly thinner under the oceans, and thicker under the continents. Partly for this reason, the earth’s crust has been divided into two separate types of crust: oceanic crust and continental crust. Oceanic crust is made up of mostly basalt, while the continental crust is made up of mostly granite. The continental crust gets as thick as 60 kilometers, while the oceanic crust does not exceed 10 kilometers in thickness. The crust is mainly composed of igneous rocks, metamorphic rocks and sedimentary rocks. The hydrosphere is essentially a sphere of water that encompasses Earth. It contains all of Earth’s water whether it is in the oceans, or buried deep in the crust. The oceans, which make up most of the hydrosphere, have a three-layer vertical structure. The first layer is known as the surface layer, and ranges from approximately 50-1000 meters deep. The second layer is called the thermocline, and is a transitional zone from the well-mixed surface layer to the deep, abyssal ocean. The third layer is known as the deep ocean, or abyssal waters. This layer occupies the majority of the ocean. The abyssal waters are fairly close to four degrees Celsius, because that is the temperature at which water is most dense. The water tends to be saltier in the deep ocean, and the currents are slow, broad and ill defined. The last component of the Earth System is the atmosphere. Earth has most likely had three or more atmospheres that have changed throughout Earth’s history. The atmosphere Earth has today was attained approximately 400 million years ago. It is composed of mostly Nitrogen (78.08%). Other elements that make up the Earth’s atmosphere are Oxygen (20.95%), Argon (.93%), and Carbon Dioxide (.036%). Traces of chlorofluorocarbons, methane, nitrous oxide and sulfur dioxide can be found in Earth’s atmosphere, as well. Earth’s atmosphere has a vertical structure that is divided into the troposphere, stratosphere, mesosphere, and thermosphere. The troposphere contains 90% of the gas in the atmosphere, and is the layer in which almost all human activity and weather occur. The troposphere begins at the earth’s surface, and rises to 20 kilometers over the equator and to about 10 kilometers over the poles. The variance in the height of the troposphere is due to the elliptical shape of Earth’s atmosphere. The stratosphere exists from 10-20 kilometers to 50-80 kilometers above Earth’s surface. Here O2 is converted to O3, which makes up the ozone layer. The ozone layer absorbs UVB radiation, the type of radiation that kills germs and causes skin cancer. Above the stratosphere is a section of Earth’s atmosphere known as the stratopause. The stratopause is the transitional part of the atmosphere that separates the stratosphere from the mesosphere. The mesosphere ranges from 50-80 kilometers above Earth’s surface to approximately 100 kilometers above Earth’s surface. Here the temperature drops as the elevation increases, similar to the troposphere. The higher into the mesosphere you go, the colder and thinner the air gets until you reach the thermosphere. The thermosphere extends from approximately 100 kilometers above Earth’s surface to space. Here the air is the thinnest and the temperature the coldest of any part of Earth’s atmosphere. Little activity exists in the thermosphere and parts of this region act almost as a vacuum.
Each inanimate component of the Earth System is coupled to the other two. A good example of this is the Hydrologic Cycle. The Hydrologic Cycle explains how water is transported about Earth. It incorporates the atmosphere, the geosphere and the hydrosphere. For example, a water molecule could start in the ocean (part of the hydrosphere) and be transported to the marine atmosphere by evaporation. The water molecule may now exist in the troposphere, and be transported over land (to the terrestrial atmosphere) in the form of a rain cloud (through atmospheric transportation). If it rains, the water molecule could make it to a surface water reservoir, where it could then be transported to a ground waters reservoir (by means of percolation) deep in Earth’s crust—part of Earth’s geosphere. Earth’s hydrosphere and geosphere are also connected through plate tectonics. Much of the ocean floor acts as a conveyor system. This system moves from the mid-ocean ridges and spreading centers to subduction zones along the margins of the continents. The accumulated load of sediments along the ocean floor is carried down into the mantle, part of Earth’s geosphere. There the subducted sediments melt and are altered chemically. Much of the new material is exposed again on Earth’s surface in magma in volcanic eruptions. As these examples illustrate, the Earth System is a complex one in which each inanimate component of that system is clearly interconnected.
2. Differentiation, in this context, means the
separation of heavier elements and lighter elements to form the structures of
the geosphere. Earth started as an undifferentiated mass, or
“proto-Earth.” This “proto-Earth” was
most likely a uniform accumulation of silicon, iron, magnesium and oxygen
compounds. The undifferentiated mass
grew more massive as more planetesimals collided with it. Heat energy was also generated from the
colliding planetesimals, which made the undifferentiated mass begin to melt. Internal energy was also produced from decay
of radioactive elements and compressional heating. Under its own gravitational field, the heavier elements, such as
iron and nickel, sank to the center of the earth to form the core. As the core was being formed, a large
quantity of energy was released as iron changed from liquid to solid. This latent heat of fusion caused all of the
undifferentiated mass to melt. The
lighter elements, such as silicon and aluminum, rose toward the surface of the
earth and formed the mantle and crust.
Together, the core, mantle and crust make up the structure of the
Earth’s geosphere.
3. The oceans don’t just get saltier and
saltier because salt is lost in the oceans through abiotic and biotic processes
and the Hydrologic Cycle keeps the levels of salt balanced. For example, the oceans get saltier because
runoff from rivers dissolves minerals that have built up from the soil, and
salt is formed. This runoff reaches the
oceans, and makes the levels of salt in the ocean increase slightly. This increase in salt can be counterbalanced
in a number of ways. For example, it
could rain above the ocean, increasing the level of fresh water found in the
ocean, which in turn decreases, or offsets, the level of salt in the ocean. There are many “loops” such as this one in
the Hydrologic Cycle. Together they
keep the world oceans from getting saltier and saltier. Salt is also lost through abiotic and biotic
processes. An example of how the level
of salt is decreased through an abiotic process is when salt forms with ocean
water and other minerals, and falls to the bottom to form sediment. This precipitation of the minerals occurs
when the concentration of those minerals gets high enough. Biotic processes include animal
processes. Minerals (salt included) are
removed through the death or excretion of an animal.
4. Around 4.5 billion years ago, Earth’s
atmosphere was composed mostly of CH4 (methane) and NH4
(ammonia). This atmosphere was formed
from the original planetesimals that formed Earth. When our sun “ignited” and evolved into a yellow star, a reactive
solar wind was cast across Earth that burnt off Earth’s atmosphere. Around 4 billion years ago a new atmosphere
formed around Earth that was composed mostly of CO2, which in part came from
volcanoes. Erosion was extensive and
rapid under Earth’s new atmosphere.
There were no plants to produce oxygen, and the atmosphere was too
underdeveloped to filter out UV radiation, so the only place life could exist
was in the oceans. The first fossils
were formed around 3.8 billion years ago, when life first appeared. At this time photosynthesis, a process that
supplies O2 first occurred. Large amounts of iron gradually built up
from erosion and were dumped into the oceans.
Rust and large sediments known as “red beds” began to gather on the
ocean floor. After approximately 1.8
billion years, the iron oxides had oxygenated the oceans to the point where
oxygen started to leak to the ocean surface and up into the atmosphere. At this time, complex plants had formed and
were drawing CO2 from the atmosphere. Over the next billion years, the levels of
oxygen slowly but steadily increased in the atmosphere. Shells and bones made of carbon compounds
like CaCO3 began to combine with the
CO2 the complex plants drew
in. This combination formed limestone
and gypsum. The O2 from photosynthesis got so
concentrated it began to form O3, also
known as ozone. At this time the level
of CO2 in Earth’s early atmosphere
was decreasing rapidly and O3 was
increasing steadily, which formed the ozone layer—Earth’s protective
atmospheric layer against UV radiation.
The harmful UV radiation was filtered out enough for life to first
appear on land around 800 million years ago.
Plants began to grow and flourish on land. Since plants take CO2 out of the atmosphere and add oxygen, the levels of oxygen in the
atmosphere continued to increase.
Today, our atmosphere consists of Nitrogen (78.08%), Oxygen (20.95%),
Argon (.93%) and Carbon Dioxide (.036%).
Nitrogen is a very stable gas that doesn’t react with anything very
easily. For this reason, it is very
difficult for any living thing to utilize.
Lightning can break down the nitrogen to nitrogen bond, which produces
things we can utilize such as fertilizer.
It is unclear why the levels of each gas in today’s atmosphere are what
they are. There is a balance mechanism
at work, but it is unknown.
5. The primary role in Earth’s climate played
by the hydrosphere and atmosphere is to transport heat from the tropics to the
poles, and elsewhere. This keeps Earth’s
climate in balance. Heat is transported
in the hydrosphere by warm currents such as the gulf stream, and by warm water
vapor that is transported atmospherically.
Heat is transported in the atmosphere in water vapor that is contained
in clouds. The hydrosphere also acts as
a “thermal battery” which allows Earth’s climate to change only
moderately. Water accomplishes this
task because it has a very high specific heat—a large quantity of energy is
necessary to either raise or lower water one degree. Water is a good storage medium of heat energy because of
this.
6. William H. Calvin’s article entitled “The
Great Climate Flip-flop” discusses how global warming trends could lead to an
abrupt, catastrophic cooling. Calvin
elaborates on many aspects of this phenomenon throughout nine different
sections of his article.
The first of his sections is
entitled “Keeping Europe Warm.” The
main points of this section are as follows:
·
Europe
is warmer than places in America and Canada at the same latitude because of the
merging of the warm Gulf Stream and North Atlantic currents that flows up the
Norwegian coast
·
The
westward branch of the North Atlantic current warms Greenland’s tip at
approximately 60 degrees N.
·
If
a failure in the northernmost loop of the North Atlantic current occurs, the
resulting population crash would take most of civilization with it. This is because Europe has to have certain
weather conditions to be as agriculturally productive as she is. If the warm loop failed and the weather got
colder, comparable to the weather in Canada at similar latitudes, only 1 out of
23 Europeans could be fed.
The next section of Calvin’s article is entitled
“Abrupt Temperature Jumps.” The main
points of this section are:
·
A
history of the gases found in the atmosphere, as well as changes in air
temperature over the last 250,000 years can be found deep in the ice sheets of
Greenland. The evidence found suggests
that global climate changes occur frequently and abruptly. The most likely cause of these changes is a
sporadic problem in the North Atlantic Ocean.
·
The
most recent big cooling started about 12,700 years ago, right after a global
warming trend. This period was called
Younger Dryas, named after the pollen of a tundra flower that showed up in a
lakebed in Denmark out of season. The
cold period lasted 1300 years then the Earth suddenly warmed up again.
·
The
Earth’s history has been plagued by unforeseen climate changes, however over
the last 8200 years Earth has had mostly moderate temperature changes. This may mean that Earth is due for a
drastic climate change.
·
On
the return loop of the North Atlantic current, massive amounts of seawater sink
below the surface at downwelling sites every winter. The “flushed” water travels south when it reaches the
bottom. A flip-flop in global climate
could occur if this annual flushing failed—much needed heat from the tropical
zones would not make it as far north as needed.
The next section of Calvin’s article is called
“Flushing Cold Surface Water.” The main
points of this section are as follows:
·
Surface
waters throughout the world are flushed regularly because water density is
dependent upon temperature. That is,
the colder the water the denser. Water
on the surface is cooled down and sinks beneath the warmer water below. Also the higher the salt content, the
heavier the water.
·
Oceans
are not mixed well. Sometimes, if a lot
of evaporation occurs, the surface water will be unusually salty and will sink
to the bottom without mixing. When this
occurs, an underwater waterfall exists like the one that flows over the ridge
that connects Spain with Morocco.
·
Another
underwater salty waterfall exists that flows from the Nordic Seas to the North
Atlantic Ocean. This fall is about 30
times the size of the Amazon river. It
exists because cold, dry winds off the coast of Canada evaporate the surface
waters of the North Atlantic, and leave behind their salt. The heavy, salty surface waters sink rapidly
and flow south. This kind of salt
sinking in the Nordic Seas is responsible for the warm current of water that
flows much farther north than it might otherwise do.
·
No
salt sinking or underwater waterfall exists in the Pacific Ocean. The Pacific is less salty than the Atlantic
because there is almost twice as much volume of water to dilute the salt from
the runoff of rivers.
The next section of William H. Calvin’s article is
called “Failures of Flushing.” Its main
points are as follows:
·
There
is a large freshwater ice sheet that exists in Greenland between the sharply
ascending mountain peaks. 20,000 years
ago similar ice sheets lay atop the Baltic Sea, Hudson’s Bay and the foothills
of the Rocky Mountains.
·
It
is possible to have a failure in salt flushing, without a comprehensive
catastrophe. For example, in the
Greenland Sea in the 1980’s, salt sinking declined by 80%. Since the water was not sinking to the
bottom and flowing south as part of the current’s loop there was less warm
water to replenish the supply when the current extended north again.
·
Reasons
for flushing failure: diminished wind chill and floating ice which leads to
less evaporation of water, which leads to lower salt content in the water. Also, if a very large quantity of fresh
water were dumped into the ocean, salt flushing could fail. Whenever flushing fails, there is always the
possibility of an abrupt climate change.
·
In
May of 1986, Alaska’s Hubbard glacier collided with Russell fjord. The glacier acted as a dam, and a lake
formed which rose higher and higher—eventually to the height of an eight-story
building. After five months the ice dam
finally broke, dumping a cubic mile of fresh water in a single day.
“The Greenhouse Connection” is the title of Calvin’s
next section, and its main points are as follows:
·
Global
climate flip-flops have happened in the past, and they’re most likely going to
happen again.
·
Changes
in temperature balance can be accounted for by studying not merely regional
shifts, but arriving and departing sunlight and heat. The temperature of Earth is in part determined by water vapor,
the most powerful greenhouse gas.
Approximately, a 30% decrease in the atmosphere’s water vapor would
result in a drop in the global temperature by at least 5 degrees Celsius.
·
If
ocean currents carried more warm waters away from the equatorial regions heat,
convection and evaporation may decrease.
This may result in a cooler equatorial region with less evaporation,
which would in turn create low levels of greenhouse gases and a global
cooling.
For
the rest of “The Greenhouse Connection,” Calvin gives modern world examples of
systems that exhibit bistable modes—light switches, thermostats and door
latches.
William H. Calvin’s next section is
very brief and is called, “Feedbacks Matter.”
The main points of this section are as follows:
·
Global
warming is an important phenomenon to combat for preventing a cold flip of the
global climate. However, other efforts
may be equally as important for achieving the same task. All of the important feedbacks that control
climate and ocean currents should be identified. These include evaporation and the reflection of light into space.
·
Feedbacks
are what determine thresholds, where one mode flips to another.
The next section of “The Great Climate Flip-flop” is
entitled “Preventing Climate Flips.”
The main points of this section are as follows:
·
It
may be possible to prevent flip-flops in the Earth’s climate with low-tech
solutions. For example, if a large
amount of freshwater starts to accumulate in the large fjords off the coast of
Greenland, as it did before, a dam could be built to stop the melt water from
entering the fjord. This may decrease
the chances of an abrupt global cooling.
·
Today,
computer models are fairly useful in predicting global climate changes and
weather patterns. However, computers
can not predict what will happen if we tamper with downwelling sites to try to
offset a global climate change.
·
Maintaining
the Earth’s current climate as best as possible is much easier than attempting
to restore Earth’s climate from an ice age to a temperate mode.
The first part of Calvin’s next section entitled,
“Three Scenarios” speculates what will happen if a global climate flip-flop
occurs. The main parts of this section are as follows:
·
A
World War III could take place if people had to fight for food and other
essential resources made scarce by a global climate flip-flop. Over 650 million people live in Europe,
which largely grows its own food. A
global climate change would result in a disruption in the food-supply routes.
·
Natural
disasters such as earthquakes and hurricanes are much less catastrophic than a
global climate change for several reasons.
First, the recovery period after an earthquake or hurricane begins the
next day, while the recovery period after a global climate change may not be
fully accomplished for several thousand years.
Second, many more people would die from a global climate flip-flop. Third, since certain nations would be much
more heavily exhausted than others, animosity and hatred toward each other may
break out.
·
It
is important for computer technology to progress in the meteorology field. If computer simulations could recreate the
ocean currents and global climate changes of our past, then we could observe
the changeover process from one global climate to another. This would in turn allow us to learn how to
counter global climate changes more effectively.
The last section of William H. Calvin’s article is
entitled, “Staying in the Comfort Zone.”
The main points of this section are as follows:
·
Stabilizing
Earth’s flip-flopping climate is difficult.
Reducing carbon dioxide emissions may help counter global warming.
·
Predicted
consequences of global warming include stronger storms, methane release,
habitat changes, ice-sheet melting, rising seas, stronger El Ninos, abrupt and
catastrophic cooling and intense heat waves.
·
We’re
most likely at the end of our present warm period. Pollution affects the climate, but does not have the sole
influence on it. Our goal should be to
make sure that enough equatorial heat flows to the waters of Norway and
Greenland. This may stabilize the
climate and create a wider comfort zone.
Since we don’t know when this global climate change will occur, it is
probably a good idea to start learning about how to counter it in the years
immediately ahead. To do this, we must
study the climate of the last 8000 years and discover what allowed it to stay
stable for so long.
William H. Calvin’s article entitled “The Great
Climate Flip-flop” is a well-organized, well-documented work. It discusses many salient aspects of the
Earth’s system that are rarely talked about, and proposed several plans of
action for Earth if a global climate change did occur. The article is presented in an interesting
manner, and presents some very horizon-broadening information.
http://www.esse.ou.edu/
http://williamcalvin.com/1990s/1998AtlanticClimate.htm
http://lists.gardencity.net/listproc/archives/acra-l/9712/0015.html
ALL
OF MY LECTURE NOTES!!! :O)