"A gamma-ray burst originating within 6,000 light years from Earth would have a devastating effect on life," said Dr. Adrian Melott of the Department of Physics and Astronomy at the University of Kansas. A gamma ray burst, if it were close enough, could do all kinds of things.

Exposure to high doses of radiation over a short period of time can cause radiation sickness (sometimes called radiation poisoning or acute radiation syndrome) and even death. They’re so powerful that even supernovae appear weak in comparison. The effects of gamma-ray bursts (GRBs) on humans and land-based life could be disastrous as the eradication of the ozone layer would leave us exposed to … To get some idea of the amount of energy we’re talking about here, consider this: the amount of energy that a gamma-ray burst generates in 10 seconds is more energy than the Sun will emit in its
What's most surprising is that just a 10-second burst can cause years of devastating ozone damage."

"We don't know exactly when one came, but we're rather sure it did come -- and left its mark.

Do x-rays and gamma rays cause any other health problems? Now, the most notable thing about a gamma-ray burst is that it is insanely energetic. Image caption Gamma-ray bursts can occur when two neutron stars merge . Gamma ray burst earth facts and information astrophysicists pin down jet from merging neutron stars record breaking gamma rays reveal secrets of the universe s what would hen if the earth were hit by a grb gamma ray watch how gamma ray bursts could wipe out life on earth How Deadly Would A By Gamma … Because the photons comprising gamma radiation are so energetic, their effect on human … Similar to X-rays, gamma rays can get past even some of the densest materials in use, making them both a great benefit and a hazard.
It could damage the Earth's electromagnetic field and that could lead to disrupted electronic communications (similar to a CME or solar storm), increased mutations in plants and animals (gamma rays can damage the DNA molecule), increased cancers, and possibly weather anomalies. A gamma ray burst, the most powerful explosion known in the Universe, may have hit …

What problems occur depend upon the radiation dose, the timing of the exposure, and what areas of the body are exposed. Gamma radiation is the most penetrative type of energy currently known.