Download Honors Earth Science Name Biogeochemical Cycles Carbon: In the

Honors Earth Science
Biogeochemical Cycles
Name __________________________________
Carbon: In the Short and Long Runs 15 points
Earth’s biosphere is based on carbon and the thousands of organic compounds this element can
form, just as Earth’s lithosphere is based on silicon and the many minerals that it can build.
Breathe In Breathe Out The short term cycling of carbon begins with carbon dioxide and the
process of photosynthesis. Our atmosphere is mostly made of nitrogen and oxygen, but there is a
small amount of carbon dioxide (.04%) in the
air too.
Photosynthesis
Photosynthesis is a complex series of
reactions carried out by algae,
phytoplankton, and the leaves in plants,
which utilize the energy from the sun. The
simplified version of this chemical reaction is
to utilize carbon dioxide molecules from the
air and water molecules and the energy from the sun to produce a simple sugar such as glucose
and oxygen as a by product. The simple sugars are then converted into other molecules such as
starch, fats, and proteins, etc. In fact, all of the "matter/stuff" of a plant ultimately is produced as a
result of this photosynthesis reaction.
Summary statement: During photosynthesis plants remove carbon dioxide from the atmosphere
and produce oxygen.
Respiration/Combustion/Decomposition
Respiration occurs in animals and plants
after the intake of oxygen and the ingestion
of organic foods. In the cells a series of
complex reactions occurs with oxygen to
convert glucose sugar into the products of
carbon dioxide and water and ENERGY.
Combustion occurs when any organic
material is reacted (burned) in the presence of oxygen to give off the products of carbon dioxide
and water and ENERGY. The organic material can be any fossil fuel such as natural gas (methane,
CH4), oil, or coal. Other organic materials that combust are wood, paper, plastics, and cloth.
Organic materials contain at least carbon and hydrogen and may include oxygen.
Summary statement: During respiration and combustion, oxygen is taken in and carbon dioxide is
released. The whole purpose of both processes is to convert chemical energy into other forms of
energy such as heat.
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Decomposition
This reaction is also carried out by bacteria in the decomposition/decay of waste materials on land
and in the water.
As described above, an individual carbon atom could cycle very quickly if the plant takes in carbon
dioxide to make food and then is eaten by an animal, which in turn breathes out carbon dioxide.
Carbon might also be stored as chemical energy in the cells of the plant or the animal. If this
happens, the carbon will stay stored as part of the organic material that makes up the plant or
animal until it dies. Some of the time, when a plant or animal dies, it decomposes and the carbon
is released back into the environment. Other times, the organic material of the organism is buried
and transformed over millions of years into coal, oil, or natural gas. When this happens, it can take
millions of years before the carbon becomes available again.
Fossil Fuels
In the natural carbon cycle, there are two main processes which occur: photosynthesis and
respiration. Humans impact the carbon cycle during the combustion of any type of fossil fuel,
which may include oil, coal, or natural gas. Fossil Fuels were formed very long ago from plant or
animal remains that were buried, compressed, and transformed into oil, coal, or natural gas. The
carbon is said to be "fixed" in place and is essentially locked out of the natural carbon cycle.
Humans intervene during by burning the fossil fuels. During combustion in the presence of air
(oxygen), carbon dioxide and water molecules are released into the atmosphere.
1. What would the effects of too much photosynthesis be on the environment?
2. What would the effects of too much respiration be on the environment?
3. How can carbon cycle very quickly back into the environment?
4. Explain how the combustion (burning) of fossil fuels affects the short term carbon cycle.
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Oh say can you C The cycling of carbon through the geosphere, atmosphere, hydrosphere and
biosphere is summarized in the figure below and tables 1 and 2.
5. In the absence of human activity, what fraction of Earth’s carbon is in motion in a given year?
6. Compare the rates of creation (precipitation) and destruction (weathering) of carbonate rocks
(limestone, gypsum). Is the carbonate rock reservoir growing or shrinking? How fast?
7. What is the residence time of carbon in carbonate rocks? Use the rate of carbonate
weathering in your calculation.
8. Which carbon reservoir is rapidly being depleted by humans? By how many times do output
fluxes exceed input fluxes?
COMPONENTS OF EARTH’S CARBON CYCLE
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Cold Storage Many types of geologic evidence indicate that Earth’s
climate has alternated between warmer and colder periods in the past.
Glacial deposits in the North American continent record the most recent period of global cooling
between 10,000 and 20,000 years ago.
The causes of these climatic fluctuations are not fully understood, but there is strong evidence
that periods of relatively high global temperature have been associated with high levels of
atmospheric carbon dioxide (CO2). Carbon dioxide is a greenhouse gas – it allows incoming shortwavelength light energy from the sun to pass through the atmosphere but does not allow longerwavelengths heat energy that is reflected back from Earth to return to space. So, heat becomes
trapped near the surface of the planet.
9. What process in Earth’s carbon cycle has apparently kept Earth from becoming too warm?
Hint: What is the largest carbon reservoir on Earth? Refer to table 1 to answer this question.
10. Previously, during the Common Rocks Lab Activity, you examined and identified some carbonbearing minerals. Samples of these rocks are on trays in the back of the room. These carbonates
represent some of the reservoirs where carbon is stored in sold form for long periods of time.
Briefly describe the physical characteristics and uses of each. Use the Internet to find uses if
needed.
Mineral/Rock
Calcite
Physical properties
Uses
Limestone
Marble
Coal (Bituminous)
During the Common Rock Lab, you also tested these rocks for a response to acid (hydrochloric
acid, HCl). Calcite, Limestone and Marble all reacted with fizzing. This indicates that a gas is being
given off as HCl chemically reacts with the rock. What gas is it? ____________________
Remember that these rocks consist mainly of the mineral calcite. Read the information about
acids/bases/pH on the next page
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Acids, Bases and pH and Carbon
In aqueous solutions, some water
molecules separate into two
kinds of ions, H+ and OH-. An
acid os a solution in which the
amount of H+ ions is greater
than OH- ions. In a base, the
reverse is true. The pH is a
measure of the concentration of
H+ ions (pH stands for potential
of Hydrogen). Acid values have
pH < 7 and bases have pH >7,
with pH = 7 being neutral.
When you put HCl on the
limestone, you simulate chemical
weathering of this carbonate
rock. The stored CO 2 in the rock
is released.
All rainwater is slightly acidic
due to carbonic acid formed from
water and carbon dioxide.
11. On times scales of days or weeks, carbon cycling occurs on and
above the Earth’s surface as carbon is exchanged between air,
water, soil and living organisms. But over the long term, the carbon
cycle is controlled by processes deep within the Earth.
Which of the fluxes in Table 2 are directly related to plate tectonic
processes? Do these tend to increase or decrease the amount of
CO2 in the atmosphere?
12. Earlier this year, you calculated the different rates of the Pacific
Plate movement using the Hawaiian Islands movement over an
oceanic hot spot. During the Cretaceous period (65 to 144 million
years ago) there was unusually rapid plate movement /seafloor
spreading rates at all of the mid-ocean ridges and had a variety of
global consequences. The graph below shows seawater
temperatures for the past 100 million years. When were the
temperatures highest?
What is the overall trend in temperatures since the Cretaceous?
When was there a significant reversal in this trend?
Limestone + hydrogen ions =
(acid)
CaCO3
+
H+
=
Calcium
+ Bicarbonate
Ca++
+ HCO3-
DEEP SEA TEMPERATURES
FOR THE LAST 100 MILLION YEARs
The effects of the acid on the
limestone result in calcium and
bicarbonate to be released and
carried to the ocean.
Dinosaurs thrived in
the warm cretaceous
climate, occupying
even Antarctica and
Northern Alaska!
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Mountain Air Precipitation of carbonate rocks like limestone extracts CO2 from Earth’s
atmosphere and keeps it out of the carbon cycle for long periods of time. Eventually, this carbon
is returned to the atmosphere (by way of faults in the Earth’s crust) if the carbonate rocks undergo
metamorphism at a convergent plate boundary. Metamorphism of limestone (with some silica
and quartz present) can be written as the following chemical equation:
CaCO3
+
SiO2
Calcite
Silica
(quartz)
=
CaSiO3
Wollastonite
(silicate mineral)
+ CO2
Carbon Dioxide
(limestone)
13. Based on the equation above, what effect do you think widespread metamorphism of
carbonates would have on climate? Explain.
Another carbon flux related to plate tectonics is the rate of rock weathering. As mountains grow
during a continental collision, erosion rates accelerate in response to steeper topography,
increasing the amount of surface area available for chemical weathering. As you found out when
you put hydrochloric acid on the limestone, chemical weathering on carbonate rocks releases CO 2
into the atmosphere. However, chemical weathering of silicate rocks, which make up most of the
continental crust, removes CO2 from the air through reactions like:
CaSiO3
Silicate
mineral
+
CO2
dissolved
in rainwater
=
CaCO3
+
Calcite
dissolved
in river & streams
SiO2
Silica
(quartz)
14. How is this chemical equation related to the previous one?
15. What can you conclude about the process of chemical weathering and metamorphism?
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012
Table 1
CARBON
RESERVOIRS
(SINKS)
Table 2
CARBON
FLUXES
From “The Blue Planet An Introduction to Earth System Science Second Edition”
Skinner, Porter and Botkin, 1999.
Edited by Leslie Joseph 2012