© Simon Redfern
Volcanism, driven by plate tectonics, built Earth’s atmosphere to make a habitable planet.
How is it that Earth developed an atmosphere that made the development of life possible? A study published in the journal Nature Geoscience
links the origins of Earth's nitrogen-rich atmosphere to the same tectonic forces that drive mountain-building and volcanism on our planet. It goes some way to explaining why, compared to our nearest neighbours, Venus and Mars, Earth's air is richer in nitrogen.
The chemistry of the air we breathe is, at least partly, the result of billions of years of photosynthesis. Plant life has transformed our world from one cloaked in a carbon dioxide-rich atmosphere - as seen on Mars or Venus - to one with significant oxygen. About a fifth of the air is made up of oxygen, and almost all the rest is nitrogen. But the origins of the relatively high nitrogen content of Earth's air have been something of a mystery.
Geoscientists Sami Mikhail and Dimitri Sverjensky of the Carnegie Institution of Washington have calculated what nitrogen is expected to do when it is cycled through the rocks of the deep Earth by the churning cycle of plate tectonics. Active volcanoes not only shower volcanic rock and superheated ash as they erupt molten rock into the air, they also vent huge amounts of gas from Earth's depths. The latest eruptions in Iceland, for example, have been noted for the amounts of sulphurous fumes that they have emitted.
Alongside sulphur, steam and carbon dioxide, volcanoes next to active tectonic plate boundaries pump massive quantities of nitrogen into the air. Mikhail and Sverjensky explain this through the chemistry of what goes on beneath those volcanic roots.