Cosmogenic

Cosmogenic is an adjective applied in geology, geophysics, and astrophysics to describe processes, products, or phenomena produced by cosmic rays. The term is most often used with cosmogenic nuclides, rare isotopes formed when high-energy cosmic rays interact with atomic nuclei in the Earth’s atmosphere or in surface rocks. The dominant production mechanism is spallation, where cosmic-ray protons and heavier ions break apart target nuclei; muons and secondary neutrons can contribute to additional production at shallow depths.

Cosmogenic nuclides occur in two main contexts. Atmospheric production creates isotopes such as radiocarbon (14C), beryllium-10 (10Be), and chlorine-36 (36Cl), which are dispersed by atmospheric circulation and measured in air, ice cores, and sediments. In situ cosmogenic production happens within exposed rock and minerals near the surface, generating isotopes such as 3He, 10Be, 26Al, and 36Cl directly in the material. These nuclides serve as tracers of surface processes and exposure histories.

Applications of cosmogenic nuclides include dating of landscapes and rocks (exposure dating), estimation of erosion and burial rates, and reconstruction of past solar activity and cosmic-ray flux from ice cores and other archives. Production rates vary with solar modulation, geomagnetic field strength, altitude, and latitude, requiring scaling models to compare measurements from different environments. Because many cosmogenic isotopes have long half-lives, they enable timescales ranging from thousands to millions of years, making them valuable tools across Earth sciences and planetary studies.