The carbon cycle describes the process by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon exists in different forms as it moves through the carbon cycle, including carbon dioxide in the atmosphere, carbon in living organisms, carbon dissolved in the ocean, and carbon stored in fossil fuels underground. The same carbon atoms are reused as they are exchanged between these reservoirs through various natural processes like photosynthesis, respiration, decomposition, and combustion.

1. THE CARBON CYCLE

2. What Is Carbon?
An element (C)
The basis of life of earth
Found in rocks, oceans, atmosphere

3. Carbon Cycle
The same carbon atoms are used
repeatedly on earth. They cycle between
the earth and the atmosphere.

4. 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).

5. Animals Eat Plants
When organisms eat plants, they take in
the carbon and some of it becomes part
of their own bodies.

6. 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.).

7. Carbon Slowly Returns to Atmosphere
Carbon in rocks and underground
deposits is released very slowly into the
atmosphere.
This process takes many years.

8. Cycle – Repeats Over and
Over and Over and Over …

9. Carbon Cycle Diagram
Carbon in Atmosphere
Plants use
carbon to make
food
Animals eat
plants and
take in
carbon
Plants and
animals die
Decomposers
break down dead
things, releasing
carbon to
atmosphere and
soil
Bodies not
decomposed —
after many
years, become
part of oil or
coal deposits
Fossil fuels are
burned; carbon
is returned to
atmosphere
Carbon slowly
released from
these substances
returns to
atmosphere

10. 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.

11. The Carbon Cycle

12. 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

13. What We Need to Do
Burn less, especially fossil fuels
Promote plant life, especially trees

14. •Good News: Air is 78% nitrogen.
•Bad News: Organisms cannot use pure nitrogen.
•How is the problem “fixed”? It must be combined with other elements into a usable form.
Nitrogen-fixing bacteria
Combine nitrogen with
other elements to make it
usable by organisms
Decomposer bacteria
Break down nitrogen
compounds in waste and
dead organisms so it can
be returned to the soil
Denitrifying bacteria
Break down nitrogen
compounds in the soil
and release back into
the air
Lightning also fixes
nitrogen by combining
it with oxygen. It then
falls down with rain in
a usable form.
Blue Arrows –
Usable nitrogen
Red Arrows –
Unusable free
nitrogen