Gamma rays are high-frequency waves emitted by stars and radioactive substances. Because the waves can easily pass through most material, avoiding gamma ray exposure requires a shield of lead or concrete. High-intensity gamma-ray bursts can come from bombs, supernovas and equipment used to treat cancer. High levels of gamma ray exposure has negative health effects on living tissue and cells.
When gamma rays pass through the human body, they ionize the tissue. This method commonly kills cancerous cells, but gamma ray ionization can affect healthy cells. When high levels of gamma rays bombard a body, a resulting dangerous ionization of tissue can cause skin cancer.
Ionization from gamma rays can cause three different reactions in living cell tissues. A cell can either perfectly repair itself and continue unharmed, it can die in the process of reproduction or it can repair itself imperfectly, causing it to reproduce abnormally or become radioactive. When a cell repairs itself imperfectly or becomes radioactive, it can develop into leukemia or a solid tumor.
Gamma Ray Bursts
If a gamma ray burst hit the Earth at high intensity, it would negatively interact with the upper atmosphere, creating nitrogen oxides that would lead to the destruction of the Earth's ozone layer. After a few centuries, the after-effects would cause a storm of cosmic rays to destroy everything on the surface of the Earth.