Living Reference Work Entry

Encyclopedia of Astrobiology

pp 1-6

Date: Latest Version

Nitrogen Isotopes

  • Ko HashizumeAffiliated withDepartment of Earth and Space Sciences, Osaka University Email author 


Nitrogen cycle (biological) Isotope anomaly Isotope fractionation Organic formation Solar composition


Nitrogen has two stable isotopes, nitrogen-14 and -15. The abundance ratios of the two isotopes among geological samples, both extraterrestrial and terrestrial, exhibit wide variations, despite the first-order expectation of its stable nature. This expectation derives from the absence of important sinks or sources of these nuclides by any known nuclear reactions that may naturally occur, apart from their nucleosynthesis in several kinds of stellar environments. Nitrogen is one of the most important elements in organic matter preserved in geological samples. The isotopic variations of nitrogen may provide important clues to decipher the formation processes for these samples.


The abundance ratios of nitrogen-14 and -15 among extraterrestrial samples exhibit more than a factor of 2 variation, the largest among all elements except for hydrogen. Interesting isotopic variations are also observed among nitrogen from various terrestrial samples that represent the compositions ...

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