Fig. 1. The N-isotopic composition (δ¹⁵N) of cosmochemical and geochemical reservoirs.

a, b Earth’s mantle δ¹⁵N, inferred from fibrous diamonds and mid-ocean ridge basalts, converges towards a globally uniform value of −5‰; however, in some mantle peridotite diamonds, the δ¹⁵N are as low as −40‰, which are comparable to EC δ¹⁵N. The positive OIB δ¹⁵N are regarded to be primordial features of Earth’s deep mantle³⁰. Earth’s sediments and crust also show positive δ¹⁵N. Solar wind (SW) and comets show extremely negative and positive δ¹⁵N, respectively. Note that Earth’s atmosphere δ¹⁵N is zero. All δ¹⁵N data were taken from references compiled in Supplementary Note 1.