The atmosphere (air) that
surrounds the Earth is
made up mainly of
nitrogen, oxygen CO2 and
Argon
the relative
proportions of the
main gases in the
atmosphere are
approximately 78%
nitrogen, 21% oxygen
and 1% argon
other gases or particulates may
be released into the atmosphere
by human activity or by natural
processes (eg volcanoes), and that
these can affect air quality
the Earth’s early atmosphere was
probably formed by volcanic activity
and consisted mainly of carbon dioxide
and water vapour
water vapour
condensed to form the
oceans when the Earth
cooled
the evolution of
photosynthesising
organisms added oxygen to,
and removed carbon
dioxide from, the
atmosphere.
carbon dioxide was
removed from the
atmosphere by dissolving
in the oceans and then
forming sedimentary
rocks, and by the
formation of fossil fuels
human activity has changed the
composition of the atmosphere
by adding a small amounts of
carbon monoxide, nitrogen
oxides and sulfur dioxide to the
atmosphere and extra carbon
dioxide and small particles of
solids (eg carbon) to the
atmosphere
some of these substances,
called pollutants, are directly
harmful to humans reduces the
amount of oxygen that blood
can carry), and that some are
harmful to the environment and
so cause harm to humans
indirectly (eg sulfur dioxide
causes acid rain).