Cosmic rays have caused radioactivity on Earth. This article discusses how cosmic radiation affects terrestrial and extraterrestrial materials. Cosmic rays consist of particles like protons, alpha particles, and heavier nuclei. These particles can cause nuclear changes in materials they interact with. Most of these changes occur in the Earth's atmosphere, where nucleons are the main cause of nuclear transformations. The outermost layer of the Earth's crust also experiences nuclear transmutations, mainly due to nucleons and pions. The rate of these transformations is much lower than in the atmosphere, but the Earth's surface contains elements not present in the atmosphere, making these changes important for certain isotopes. For example, chlorine-36 is produced in the atmosphere but most of it comes from neutron capture in the ocean and rocks. Deeper in the Earth, interactions with muons and neutrinos may cause isotopic changes, though these are hard to detect with current technology. Extraterrestrial material, such as meteorites and interplanetary dust, has also been affected by cosmic rays. These materials may show chemical and isotopic anomalies due to prolonged exposure. The composition of cosmic rays has been altered by nuclear collisions and interactions with interstellar gas. Interplanetary dust contributes the most to extraterrestrial material, with about 10,000 tons per day. Meteorites and meteoroids contribute less. The study of isotopic changes in extraterrestrial materials, such as meteorites and tektites, is important for understanding the history of cosmic radiation and the accretion process. Meteorites show the largest cosmic ray-induced changes because their reaction products have accumulated over long periods. The presence of radioactive isotopes and abnormal stable isotope abundances can help determine past cosmic radiation intensity, energy spectrum, and radiation dose.Cosmic rays have caused radioactivity on Earth. This article discusses how cosmic radiation affects terrestrial and extraterrestrial materials. Cosmic rays consist of particles like protons, alpha particles, and heavier nuclei. These particles can cause nuclear changes in materials they interact with. Most of these changes occur in the Earth's atmosphere, where nucleons are the main cause of nuclear transformations. The outermost layer of the Earth's crust also experiences nuclear transmutations, mainly due to nucleons and pions. The rate of these transformations is much lower than in the atmosphere, but the Earth's surface contains elements not present in the atmosphere, making these changes important for certain isotopes. For example, chlorine-36 is produced in the atmosphere but most of it comes from neutron capture in the ocean and rocks. Deeper in the Earth, interactions with muons and neutrinos may cause isotopic changes, though these are hard to detect with current technology. Extraterrestrial material, such as meteorites and interplanetary dust, has also been affected by cosmic rays. These materials may show chemical and isotopic anomalies due to prolonged exposure. The composition of cosmic rays has been altered by nuclear collisions and interactions with interstellar gas. Interplanetary dust contributes the most to extraterrestrial material, with about 10,000 tons per day. Meteorites and meteoroids contribute less. The study of isotopic changes in extraterrestrial materials, such as meteorites and tektites, is important for understanding the history of cosmic radiation and the accretion process. Meteorites show the largest cosmic ray-induced changes because their reaction products have accumulated over long periods. The presence of radioactive isotopes and abnormal stable isotope abundances can help determine past cosmic radiation intensity, energy spectrum, and radiation dose.