of the gas, and melted the ice shells to form
carlsbergite.
A similar process may have occurred for
the formation of the Earth. 4.6 billion years
ago, an astronomically large nebula (a cloud
of dust and ice), may have collapsed due
to turbulence, which heated up the centre,
increased the spin and condensed the dust
and gas into the protoplanetary disc [2]. Harries
and his team propose that the primordial ice
(prehistoric ice) may have been dragged to
the inner portions of the Solar System in the
protoplanetary phase, during which ammonia
was evaporated and bombarded by small
bodies , formi ng car l sberg i te - contai n i ng
bodies. As our planet is located in the inner
Solar System, it is possible that the primordial
ice may have accumulated on Earth during its
formation [4]. NASA’s Dawn spacecraft
recently entered the orbit around
the dwarf planet Ceres, which
is located within the asteroid
belt. The team is expecting to
collect samples on asteroids for
further matching of nitrogen’s
isotopic signature to provide
more support to these theories, among other
projects.
Whi le the or igin of nit rogen remains a
mys ter y, we can at tempt to answer the
question of why there is so much nitrogen in the
atmosphere compared to other gases. One
theory is that when the Earth formed billions
of years ago, gases readily mixed with other
chemicals to form rocks or oceans. Nitrogen,
however, i s a relat i vel y i ner t gas , wh ich
ended up settling in the Earth’s atmosphere.
Additionally, nitrogen is a diatomic molecule
and is unable to escape into space unlike
lighter molecules such as hydrogen.
Why is all of this important? Discovering
the origins of nitrogen provides information
on the age-old question of how life began or
whether biomolecules can be synthesised. So
far, attempts to create biomolecules
based on the assumptions of the
Earth’s early days have proven
to be difficult and not particularly
rel iable. But with the help of
rapidly advancing technology,
we are able to un ravel l i fe’s
mysteries little by little.
References
[1] Marty, B., Chaussidon, M., Wiens, R.C., Jurewicz, A. J. G., Burnett, D. S., A 15N-Poor Isotopic Composition for the Solar System as Shown by
Genesis Solar Wind Samples (2011).
Science
. DOI: 10.1126/science.1204656
[2] Harries, D., Hoppe, P., Langenhorst, F. Reactive ammonia in the solar protoplanetary disc and the origin of Earth’s nitrogen (2015).
Nature
Geoscience
. DOI:10.1038/ngeo2339
The History of
Nitrogen
氮的歷史
Chromium(III)-nitride
