What is the History of the Atmosphere?
We have seen how the ancient
atmosphere and oceans
have formed, how life may have started on the Earth and
how the appearance of the first green plants released oxygen
into the atmosphere through the process of photosynthesis.
The evolution of green plants and
the presence of more
oxygen produced further changes in the atmosphere.
Methane in the ancient
atmosphere would have
reacted with oxygen producing carbon dioxide and water.
Ammonia in the ancient atmosphere
would have reacted with
oxygen producing nitrogen and water. Ammonia would also have
decomposed in the presence of strong ultraviolet light
from the sun, giving more nitrogen and hydrogen. Ultraviolet light
was stronger in the past before the ozone layer had developed.
acted on ammonia to produce
for plant growth, and denitrifying bacteria added nitrogen to
the atmosphere (see the nitrogen cycle).
The proportion of nitrogen in the atmosphere steadily increased.
The increase in oxygen
and the presence of the ozone layer in
the atmosphere allowed new and more complex life forms to evolve.
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