Understanding the origin of life-essential volatiles such as nitrogen (N) in the Solar System and beyond is critical to evaluate the potential habitability of rocky planets^1,2,3,4,5. Whether the inner Solar System planets accreted these volatiles from their inception or had an exogenous delivery from the outer Solar System is, however, not well understood. Using previously published data of nucleosynthetic anomalies of nickel, molybdenum, tungsten and ruthenium in iron meteorites along with their ¹⁵N/¹⁴N ratios, here we show that the earliest formed protoplanets in the inner and outer protoplanetary disk accreted isotopically distinct N. While the Sun and Jupiter captured N from nebular gas⁶, concomitantly growing protoplanets in the inner and outer disk possibly sourced their N from organics and/or dust—with each reservoir having a different N isotopic composition. A distinct N isotopic signature of the inner Solar System protoplanets coupled with their rapid accretion^7,8 suggests that non-nebular, isotopically processed N was ubiquitous in their growth zone between 0 and ~0.3 Myr after Solar System formation. Because the ¹⁵N/¹⁴N ratio of the bulk silicate Earth falls between that of the inner and outer Solar System reservoirs, we infer that N in the present-day rocky planets represents a mixture of both inner and outer Solar System material.

了解太阳系及其他地区的生命必需挥发物（如氮 (N)）的起源对于评估岩石行星^1,2,3,4,5的潜在可居住性至关重要。然而，内太阳系行星是否从一开始就吸积了这些挥发物，还是从外太阳系外源输送，尚不清楚。使用先前公布的铁陨石中镍、钼、钨和钌的核合成异常数据及其¹⁵ N/ ¹⁴ N 比率，我们在这里表明，内、外原行星盘中最早形成的原行星吸积了同位素不同的 N。太阳和木星从星云气体⁶中捕获 N，同时在内盘和外盘中生长的原行星可能从有机物和/或尘埃中获取它们的氮——每个储层具有不同的氮同位素组成。太阳系内部原行星的独特 N 同位素特征加上它们的快速吸积^7,8表明，在太阳系形成后，非星云、同位素处理的 N 在它们的 0 到 ~0.3 Myr 之间的生长区无处不在。由于大块硅酸盐地球的¹⁵ N / ¹⁴ N 比率介于太阳系内部和外部储层之间，我们推断当今岩石行星中的 N 代表太阳系内部和外部物质的混合物。