Using Nitrogen to Study Earth’s Origins

This month in Nature Geoscience, researchers review how analysis of nitrogen isotope variation is shedding light on early Earth forming events.

Deep Carbon Observatory scientists are interested in the origins of carbon on Earth, as well as how reservoirs of carbon are stored deep inside the planet. To address these questions, they need an understanding of how Earth formed in the context of the early Solar System over 4.56 billion years ago. This month in Nature Geoscience, DCO’s Evelyn Füri and Bernard Marty (CRPG/CNRS, Université de Lorraine, Nancy, France) review how analysis of nitrogen isotope variation is shedding light on early Earth forming events [1].

Our Solar System formed as dust and gas cooled around a newly forming star, the Sun. This dust and gas was subjected to heat and magnetic turbulence, and as it rotated around the Sun, these nebulous materials reacted, forming the chemical species that would go on to form the planets, their moons, and other celestial bodies such as comets. Materials closer to the Sun reacted differently from those farther away, resulting in a distribution of different chemical species across the solar system. The reasons for such chemical gradients are not fully understood; they could result from varying interactions between matter and light from the early Sun, and/or from contrasting pressure and temperature conditions.

An important example of this differential distribution is hydrogen, the heavy isotope of which, deuterium, is enriched in objects that formed farther from the Sun. Analyzing the deuterium/hydrogen ratio on Earth, neighboring planets, and other objects in our Solar System (such as comets and meteorites) has important implications for describing the origins of water on Earth.

Similarly, scientists use analyses of nitrogen isotopes to ask questions pertaining to planetary origins. Nitrogen isotopes are particularly interesting because their distribution does not follow the same uniform pattern as deuterium. For example, on Earth’s Moon nitrogen isotope variation is an order of magnitude larger than on Earth. While the absence of an atmosphere on the Moon explains some of this effect, significant questions remain. Scientists now know that these variations are the result of mixing between ions from the Sun, depleted in the rare isotope 15N, that are continuously implanted in lunar soils, and 15N-rich material falling onto the Moon as cometary debris and micrometeorites. These variations also allow scientists to identify how volatile elements, including carbon, were deposited on planetary surfaces from extraterrestrial material.

Studying nitrogen isotope variation in the solar system is challenging. In the review, Füri and Marty detail advances in instrumentation that have revolutionized the field over the last few years. In particular, they highlight the importance of secondary ionization mass spectrometry (SIMS). SIMS allowed for high-resolution analysis of solar wind material recovered from the NASA Genesis mission. Thanks to such technological breakthroughs, the ongoing Rosetta mission is able to measure volatile elements including carbon and nitrogen in the coma of comet 67P/Churyumov-Gerasimenko.

 

Image: In this artist's conception, gas and dust - the raw materials for making planets - swirl around a young star. The planets in our solar system formed from a similar disk of gas and dust captured by our Sun. Credit: NASA/JPL-Caltech

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