Carbon is the sixth most common element in the universe and
is the main element in every living thing on Earth. Carbon atoms are passed
between living things through the CARBON CYCLE. Carbon is present
as carbon dioxide in the air, and makes up a large part of coal, crude oil, and
natural gas. Pure carbon is very rare in nature, although it can be found in
one of several different forms, or ALLOTROPES.
Anything that burns well usually contains carbon. Coal, charcoal,
wood, and paper are packed full of carbon. Carbon atoms joined together store a
lot of energy. When carbon burns, each carbon atom breaks away from its
surrounding atoms and reacts with oxygen in the air to form carbon dioxide. The
stored energy is released as heat.
The atoms of some elements can link up in different ways
to create different forms called allotropes. Carbon is found in three
allotropes: diamond, graphite, and fullerene. Each allotrope has very different
physical properties. Graphite, diamond, and fullerene contain only carbon
atoms, but the atoms are arranged differently in each allotrope.
Some lubricating engine oils and all pencil leads contain
graphite. Graphite has layers of carbon atoms that can slide across one
another. There are strong bonds between the carbon atoms of each layer, but
weak bonds between the different layers. Because the layers can move over one
another, graphite is quite a soft material.
The stable structure of fullerenes works well on large-scale
buildings. In the 1940s, architect Buckminster Fuller designed a type of
building called a geodesic dome. It is made of a network of triangles that
together form a sphere. This shape is very stable and encloses a lot of space
with little building material, making it strong but light.
Carbon atoms continually circulate through the air,
animals, plants, and the soil. This recycling of carbon atoms in nature is
called the carbon cycle. The bodies of all living things contain carbon. The
carbon comes originally from carbon dioxide gas in the air. Green plants and
some bacteria take in the carbon dioxide and use it to make food. When animals
eat plants, they take in some of the carbon. Carbon dioxide goes back into the
air when living things breathe out, and when they produce waste, die, and
decay.
Green plants use carbon dioxide from the air to make food. When an
animal eats a plant, it uses the carbon to build body tissue. When the animal
breathes out, it returns carbon into the air as carbon dioxide. When the animal
dies and decays, the carbon in its body returns to the soil. Decomposers such
as worms, bacteria, and fungi, feed on the decaying remains of animals. As they
feed, the decomposers breathe out carbon dioxide into the air. Green plants
then take in carbon dioxide from the air, and the cycle is repeated.
