THE CARBON CYCLE
What Is Carbon?
• Carbon is the chemical element with symbol C and atomic
•
•
•
•
number 6. As a member of group 14 on the periodic table,
it is nonmetallic and tetravalent—making four electrons
available to form covalent chemical bonds.
Carbon is a nonmetal that can bond with itself and many
other chemical elements, forming nearly ten
million compounds.
The basis of life of earth-all living things have it
Found in rocks, oceans, atmosphere
Carbon is the fourth most abundant element in the
universe (hydrogen, helium, and oxygen are found in
higher amounts, by mass)
Carbon
Carbon exists in the nonliving environment as:
• Carbon dioxide (CO2)
• Carbonic acid ( HCO3−)
• Carbonate rocks (limestone and coral = CaCO3)
• Deposits of Fossil fuels
• Dead organic matter
Carbon Cycle
• The same carbon atoms are used repeatedly on earth.
They cycle between the earth and the atmosphere.
Plants Use Carbon Dioxide
• Plants pull carbon dioxide from the atmosphere and use it
to make food –— photosynthesis.
• The carbon becomes part of the plant (stored food).
Animals Eat Plants
• When organisms eat plants, they take in the carbon and
some of it becomes part of their own bodies.
Plants and Animal Die
• When plants and animals die, most of their bodies are
decomposed and carbon atoms are returned to the
atmosphere.
• Some are not decomposed fully and end up in deposits
underground (oil, coal, etc.).
Carbon is released into the
atmosphere in several ways
• Respiration by plants and animals.
• Decay of animal and plant matter.
• Combustion of organic material
• Production of cement.
• The ocean releases CO2 into the atmosphere.
• Volcanic eruptions and metamorphism
Carbon Slowly Returns to Atmosphere
• Carbon in rocks and underground deposits is released
very slowly into the atmosphere.
• This process takes many years.
• See Animation
CARBON POOLS
Pool
Atmosphere
Terrestrial Plants
Soil Organic matter
Ocean
Fossil Fuel Deposits
Marine Sediments and Sedimentary Rocks
Amountin Billions of Metric Tons
578 (as of 1700)- 766 (as of 1999)
540 to 610
1500 to 1600
38,000 to 40,000
4000
66,000,000 to 100,000,000
Carbon is stored on our planet in the following major pools:
• as organic molecules in living and dead organisms found in the
biosphere;
• as the gas carbon dioxide in the atmosphere;
• as organic matter in soils;
• in the lithosphere as fossil fuels and sedimentary rock deposits such as
limestone, dolomite and chalk;
• in the oceans as dissolved atmospheric carbon dioxide and as calcium
carbonate shells in marine organisms.
2/12
Carbon Cycle
CYCLE – REPEATS OVER
AND OVER AND OVER
AND OVER …
Carbon Cycle Diagram
Carbon in Atmosphere
Decomposers
break down dead
things, releasing
carbon to
atmosphere and
soil
Fossil fuels are
burned; carbon
is returned to
atmosphere
Carbon slowly
released from
these substances
returns to
atmosphere
Plants use
carbon to make
food
Plants and
animals die
Bodies not
decomposed —
after many
years, become
part of oil or coal
deposits
Animals eat
plants and
take in carbon
Carbon in Oceans
• Additional carbon is stored in the ocean.
• Many animals pull carbon from water to use in
shells, etc.
• Animals die and carbon substances are
deposited at the bottom of the ocean.
• Oceans contain earth’s largest store of carbon.
The Carbon Cycle
Human Impact
• Fossil fuels release carbon stores very slowly
• Burning anything releases more carbon into atmosphere
— especially fossil fuels
• Increased carbon dioxide in atmosphere increases global
warming
• Fewer plants mean less CO2 removed from atmosphere
HISTORICAL ATMOSPHERIC CO2
CONCENTRATION
This figures shows that the concentration of CO2 has never been grater than 300
ppmv for the past 400,000 years.
7/12
ATMOSPHERIC CO2 CONCENTRATION-1
Accurate and direct measurements of the concentration of CO2 in the atmo
began in 1957 at the South Pole and in 1958 at Mauna Loa, Hawaii. 4/12
TRACING MATTER
Environmental Literacy
Research Group
Grandma Johnson
?
Describe the path of a carbon atom from Grandma
Johnson’s remains, to inside the leg muscle of a
coyote. NOTE: The coyote does not dig up and
consume any part of Grandma Johnson’s remains.
A Solution
• When she dies, she will be decomposed by tiny bacteria
and fungi. As this happens, carbon is released into the
soil, which in turn is taken up by the plant roots as
nutrients. The plant in turn gets consumed by a small
herbivore, who is then consumed by the coyote
• As Gma decays, carbon atoms are released into the soil.
The bush she's buried under absorbs the carbon as
nutrients. A rabbit may eat part of the bush which has the
atom in it, and then that rabbit may be eaten by the coyote
and absorbs the carbon atom into its muscles for energy
use
What We Need to Do
• Burn less, especially fossil fuels
• Promote plant life, especially trees