Page 6 - Curriculum Visions Dynamic Book

Nitrogen and the atmosphere
Nitrogen is the most abundant gas in the atmosphere, making 79% by volume and 76% by mass (weight). Nitrogen molecules are bound together so tightly that nitrogen (unlike oxygen) is undisturbed by ultraviolet radiation and is found as gas molecules in the high atmosphere.
Nitrogen was one of the first gases to be formed in the early atmosphere, some four billion years ago. The most likely source was as ammonia gas coming out of volcanoes and hot springs. The ammonia was then acted on by light, breaking down to produce nitrogen and hydrogen.
Over time the other gases of the early atmosphere were partly combined with the Earth’s rocks and oceans or, in the case
of hydrogen, disappeared into space. As
a result, the inert nitrogen was left as a greater and greater proportion of the atmosphere.
Nitrogen rarely reacts
with the other gases in
the atmosphere except at high temperatures during lightning
flashes (and in vehicle engines).
During a lightning flash, when temperatures reach 30,000°C,
nitrogen and oxygen combine to make nitrogen dioxide, which, when dissolved
in water, makes dilute nitric acid. This is
a natural (and modest) source of acid rain. At the same time it makes nitrogen into soluble products that can be absorbed by plant roots.
Nitrogen as a source
of carbon-14
In the upper atmosphere, nitrogen atoms are bombarded by cosmic rays in the form of neutrons. These change the atomic number of the nitrogen, converting nitrogen into radioactive carbon (the carbon isotope carbon-14).
Carbon-14 and oxygen atoms combine to form radioactive carbon dioxide, a gas that is absorbed by plants. In this way tiny amounts
of carbon-14 are stored by plants.
The residual carbon-14 in carbon- containing materials can be measured to determine the age of the material.
 At first the Earth had no atmosphere, but volcanic eruptions slowly produced the gases that make the atmosphere we have today, which is dominated by nitrogen.
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