A supernova can occur when the core of a massive star collapses or when a white dwarf in a binary system absorbs too much matter from its companion and a gravitational collapse is triggered. In either case, the outer body of the star explodes in a tremendous release of energy, annihilating the star's planets and lighting up the sky.
While supernovae were only officially classified in the 1930s, the earliest known observation of a supernova occurred in China in 185 AD. They are relatively rare stellar events, as most stars simply use up their fuel and cool down rather than suffer an explosion.
When stars initially form, the materials in the primordial cloud include simple elements like hydrogen and helium. When a star goes supernova, it seeds surrounding space with heavier elements. The shockwave created by a supernova can compress interstellar gas clouds, triggering the formation of young stars.
One theory about the Ordovician-Silurian extinction that occurred around 450 million years ago is that a nearby supernova flooded the young Earth with energy and damaged the ozone layer, subjecting the planet to high levels of ultraviolet radiation. Ultimately, around 60 percent of life in the oceans died due to this event.