ASTROPHYSICAL EVENTS AS EPISODIC THREATS TO LIFE ON EARTH

Astrophysical sources of high-energy radiation (including gamma-rays, X-rays and charged particles known as cosmic rays) are likely to have played a role in the development of life on Earth over. Potential impacts range from mild stress to the biosphere to the initiation of mass extinctions. We enumerate the known sources of radiation and describe the potential impacts on life on Earth's surface and in the oceans. Such impacts include direct irradiation by cosmic-ray secondaries and enhancement of solar UV radiation following stratospheric ozone depletion.