Gamma ray burst (GRB) is a burst of high energy gamma rays that is detectable from Earth's instruments when it occurs in our galaxy or a nearby one. The exact probability of a GRB hitting Earth and the potential consequences are still subjects of ongoing research and scientific debate.

However, it is generally understood that an extremely powerful and nearby GRB could have significant effects on Earth's atmosphere, ozone layer, and potentially, life on the planet. Depending on the energy and distance of the GRB, the effects could range from damage to the ozone layer, leading to increased ultraviolet radiation reaching the surface, to a potential disruption of Earth's climate and ecosystems.

It's important to note that the likelihood of such an event occurring is very low, and Earth has survived numerous such burst over its long history. However, scientists continuously monitor the sky for GRB activities, and the understanding of the potential risks is constantly evolving as new observations and research is conducted.