Earth's atmosphere is 78% nitrogen and 21% oxygen, a unique blend in the solar system. Oxygen was produced by some of the earliest living organisms. But where does nitrogen come from? Did it escape from the Earth's mantle through volcanic activity?
To try to answer these questions, an international team of researchers also from the National Institute of Geophysics and Volcanology (INGV), collected and studied gas samples from various volcanic systems on our planet, including Yellowstone, Iceland, the African continental rift. Their study “Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen”, recently published in the journal Nature, shows that nitrogen from the Earth's mantle does not have the same isotopic composition as atmospheric nitrogen, implying that the latter does not come from mantle outgassing.
“It was discovered that air contamination was masking the 'original signature' of many volcanic gas samples,” says Antonio Caracausi, INGV researcher and co-author of the research.
Without this distinction, scientists were unable to answer basic questions such as: Was nitrogen left over from Earth's formation or was it delivered to the planet later? How is nitrogen from the atmosphere related to nitrogen coming out of volcanoes?
The study is based on a new and innovative methodology for studying nitrogen isotopes. This method has provided a unique way to identify nitrogen molecules that come from the air, and has allowed researchers to pinpoint the composition of gases deep within the Earth's mantle. This ultimately revealed evidence that nitrogen in the mantle has most likely been present since our planet was initially formed. Thus, 'once air contamination was taken into account, we gained valuable new insights into the origin of nitrogen and the evolution of our planet,' says the scientist.
Furthermore, these new results made it possible to distinguish the contribution of the atmosphere (in the form of heated rainwater) from that of the earth's mantle (magmatic gas) in geysers, fumaroles and other natural manifestations of volcanic gases. For example, quantities of magmatic gas have been recognized in geysers in Yellowstone National Park, indicating renewed activity in the volcanic system.
Given the high precision of these data, they could also contribute to a deeper understanding of the magmatic processes potentially capable of generating volcanic eruptions. Samples continue to be collected at Yellowstone and other active volcanic systems around the world, including Etna which is Europe's most active volcano.
In any case, the origin of atmospheric nitrogen remains a mystery…for now.
Researchers of lost nitrogen (on planet Earth?)
