An attempt to reveal the origin of Earth's Nitrogen

Volcanic gas samples of nitrogen are contaminated by the atmosphere and a technique which was devised for determining the composition of nitrogen in the mantle, and to provide hints about the origin of the element in the earth’s interior eventually paves the way for determining and studying about volcanic activities too. Science is making another attempt for a new discovery!!!!

Nitrogen is the most abundant element in the atmosphere. It is responsible for our living and existence, still, the isotopic studies of nitrogen are not accurate enough because the samples taken from the mantle mixes with gases from the atmosphere. Researchers at Woods Hole Oceanographic Institution (WHOI), the University of California Los Angeles (UCLA) are searching for answers to this question. They had done their research using hydrothermal gases sampled from Yellowstone National Park in the United States, Iceland, and other volcanic premises. This study was supported by the Deep Carbon Observatory and the Alfred P. Sloan Foundation.

On 15th April a paper in Nature, Labidi et al.1 reported that they have used a ‘clumped isotope’ method for recognizing pure mantle nitrogen in volcanic-gas effusions and gases trapped in volcanic-rock samples.

There are two main isotopes for nitrogen (Isotopes are those with the same atomic number but the mass number is different) nitrogen-14 and nitrogen-15, among which the first one is more abundant. If we take samples from different locations there would be a difference in the relative abundance of them and the researchers claim that these differences are due to the earth formation and due to the convection of mantle. The differences in these proportions, as well as the way of arrangement of molecules, could be studied in detail to extract the information which is required.

Now let us see what is meant by clumped isotope, the combination of these isotopes to form molecules is called isotopologue.

For example here 14N-14N, 14N-15N, and also 15N-15N are the possible molecular compositions of these isotopes. The first one being the generally common one, whereas for the less stable combinations probabilities are low due to the difficulty in the substitution process of these isotopes. If a distribution is made randomly using these isotopes as well as the available dinitrogen amount, a distribution pattern corresponding to these three isotopologues would be available and the deviation from the expected result is termed as clumped isotope anomaly, and Labidi et al. used this signature to identify atmospheric contamination of volcanic gases. This ultimately showed the proof that nitrogen in the mantle has most likely been there since our planet initially formed.
WHOI geochemist Peter Barry, a co-author of the study says “Once air contamination is accounted for, we gained new and valuable insights into the origin of nitrogen and the evolution of our planet,”.

This new method helps scientists to understand the origins of volatile elements on Earth, it may also prove useful as a way of identifying and tracking the activity of volcanoes as the composition of gases coming from volcanic centres changes prior to eruptions. It could be that the mix of the mantle and air nitrogen could one day be used as a signal of eruptions.