New geochemical tool reveals origin of Earth’s nitrogen: Novel analysis method may also be useful for monitoring volcanic activity

Posted: April 19, 2020 by oldbrew in Geology, research, volcanos

As the video reminds us: Earth’s atmosphere is mostly (78%) nitrogen. Plus about 21% oxygen at sea level, and a few minor trace gases – one or two of which some people like to fixate on.

Researchers have used a new geochemical tool to shed light on the origin of nitrogen and other volatile elements on Earth, which may also prove useful as a way to monitor the activity of volcanoes, says ScienceDaily.

Their findings were published April 16, 2020, in the journal Nature.

Nitrogen is the most abundant gas in the atmosphere, and is the primary component of the air we breathe. Nitrogen is also found in rocks, including those tucked deep within the planet’s interior.

Until now, it was difficult to distinguish between nitrogen sources coming from air and those coming from inside the Earth’s mantle when measuring gases from volcanoes.

“We found that air contamination was masking the pristine ‘source signature’ of many volcanic gas samples,” says WHOI geochemist Peter Barry, a coauthor of the study.

Without that distinction, scientists weren’t able to answer basic questions like: Is nitrogen left over from Earth’s formation or was it delivered to the planet later on? How is nitrogen from the atmosphere related to nitrogen coming out of volcanoes?

Barry and lead author Jabrane Labidi of UCLA, now a researcher at Institut de Physique du Globe de Paris, worked in partnership with international geochemists to analyze volcanic gas samples from around the globe — including gases from Iceland and Yellowstone National Park — using a new method of analyzing “clumped” nitrogen isotopes.

This method provided a unique way to identify molecules of nitrogen that come from air, which allowed the researchers to see the true gas compositions deep within Earth’s mantle. This ultimately revealed evidence that nitrogen in the mantle has most likely been there since our planet initially formed.

“Once air contamination is accounted for, we gained new and valuable insights into the origin of nitrogen and the evolution of our planet,” Barry says.

While this new method helps scientists understand the origins of volatile elements on Earth, it may also prove useful as a way of monitoring the activity of volcanoes. This is because the composition of gases bellowing from volcanic centers change prior to eruptions.

It could be that the mix of mantle and air nitrogen could one day be used as a signal of eruptions.

Full article here.

  1. E.M.Smith says:

    The nitrogen came from stars / novae. Everything else is just the ride and asking “bus or truck?”.

    Triple-alpha process in stars

    Helium accumulates in the cores of stars as a result of the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle. Further nuclear fusion reactions of helium with hydrogen or another alpha particle produce lithium-5 and beryllium-8 respectively. Both products are highly unstable and decay almost instantly back into smaller nuclei, unless a third alpha particle fuses with a beryllium-8 nucleus before that time to produce a stable carbon-12 nucleus.

    Then despite carbon and oxygen dominating the reaction products; once on earth most of the CO2 ends up as carbonate rocks once life gets a hold of it. A bunch of the excess oxygen joins with the other major product, silicon, to make rocks. Mostly quartz (SiO2) derived or rocks with that and added other metals.

    Nitrogen doesn’t react well so gets left laying around as gas. Though life uses some of it, too.

    So stars make it, then a nova explosion spreads the stuff around. Gravity collects some of it into planets, then geology separates the silicates and life gets to work on the carbonates and nitrogen.

    Those folks are just asking what local bus ride moved a given bit from dirt or life to air, and what regional ride arrived at formation and which bit was later trucked in on a comet..