 Potential evidence that these effects could have been caused by a celestial event, a supernova, are observations of gamma-ray bursts and X-ray flashes have been compared to nebular records to test this, as well as supernovae flash models, comparable to the records of in-galaxy supernovae, to study the effects of such an event on Earth.These effects include depletion of the ozone layer, increased UV exposure, global cooling, and nitrogen changes in the Earth's surface and troposphere.As Brakenridge states, the only supernova possible at that time was the Vela supernova, now classified as the Vela supernova remnant.