The origin and evolution of Earth's nitrogen

Area of Science:

• Geochemistry and Planetary Science
• Biogeochemical Cycles

Background:

• Nitrogen is essential for life, influencing Earth's atmosphere and climate through its surface-mantle cycling.
• The origin and evolution of Earth's nitrogen remain incompletely understood.
• Significant nitrogen reservoirs exist in Earth's surface, mantle, and core.

Purpose of the Study:

• To review the current understanding of Earth's nitrogen budget and isotopic composition.
• To explore deep nitrogen geochemistry, origins, and the role of plate tectonics and volcanism.
• To suggest future research directions for understanding Earth's nitrogen.

Main Methods:

• Review of existing literature on nitrogen budget, isotope composition, and geochemistry.
• Analysis of laboratory constraints on deep nitrogen.
• Examination of models for nitrogen acquisition during Earth's accretion and deep cycling.

Main Results:

• Earth likely acquired nitrogen heterogeneously during accretion from various impactors.
• Mantle and core nitrogen reservoirs were established early and modified little by deep cycling.
• Early atmosphere may have had 1.4x present atmospheric nitrogen (PAN), with 0.4 PAN fixed biotically.

Conclusions:

• Earth's nitrogen budget and isotopic composition were largely set during accretion.
• The deep nitrogen cycle, including subduction and volcanism, has a limited but ongoing impact.
• Further research is crucial for a comprehensive understanding of Earth's nitrogen origin and evolution.