Ionizing radiation and water in chemical processing in the space and on the early earth

We review the sources of ionizing radiation in Space and on early Earth: cosmic rays, radioactive elements and natural nuclear reactors. Also the energies they deposit (absorbed doses) in water and water containing materials. Some general facts on the action of ionizing radiation on water and aqueous systems (ice, liquid, vapor), are given. Results of simulation experiments relevant to radiation processings of presolar material and cometary nuclei are surveyed. The results of computer simulations of radiation-induced processes in waters of early Earth are presented. We consider the radiolysis of some aqueous systems of interest to the studies of chemical evolution, and their dependence on temperature, type, and energy of radiation. Some facts obtained by direct observations of cometary nuclei, and some findings in geochemistry of early Earth, are examined in the light of results on radiation chemistry relevant to comets and primitive oceans. Future work is considered: evaluation of absorbed doses due to cosmic-rays, especially charged particles at relativistic energies: critical choice of a model system and working conditions for simulation experiments; computer simulation of chemical processes, in particular the nonhomogeneous kinetics in icy matrix. (author)