Ma k i n g
u p 7 8 % o f t h e
atmosphere, nitrogen is the most abundant
gas on Earth. It was first isolated in 1772 by a
Scottish physician, Daniel Rutherford, and is an
essential substance that allows the possibility
of life. Yet, most of Earth’s higher organisms are
unable to directly utilise atmospheric nitrogen
and instead, obtain it from food in the form
of nitric compounds. In a process known as
nitrogen fixation, diazatrophs (nitrogen fixing
bacteria) are able to convert nitrogen gas into
ammonia, nitrite and nitrate. The existence of
these microbes casts doubt on the necessity of
the enormous amount of nitrogen present in air.
The fact that it occupies such a huge fraction
The History of
of the gases present in the atmosphere calls its
origin into question.
A previous school of thought suggested
that nitrogen could have been deposited by
comets, since ammonia (NH3) is an abundant
compound in these interstellar rocks. One
method to trace the origin of an element is
to examine its isotopic signature or isotopic
compos i t i on and whether i t matches i t s
hypothesised origin. For example, the most
abundant n i t rogen i sotope i s
14
N wi th 7
neutrons, at 99.6% in the atmosphere. However,
15
N al so ex i sts as a stable i sotope, with 8
neutrons. The isotopic signature would be the
ratio between the stable isotopes. In a research
Artist’s Impression of a Baby Star Still Surrounded by a Protoplanetary Disc
i
mage credits: ESO/L. Calçada
