Humans can cause extinction through pollution, over harvesting, destroying habitats and over hunting. There are also other ways things have become extinct, such as, predators (getting eaten) and natural causes eg, volcanoes, earthquakes etc.
Dictionary: Extinction- 1. The state or process of being or becoming extinct. 2. Reduction to zero in the intensity of light or other radiation as it passes through a medium, due to absorption, reflection or scattering