Answer:
They cause significant changes that disrupt the equilibrium of the Earth and lead to natural separation points
Step-by-step explanation:
The catastrophic events in the geological past have been sued for separation of the geological time unites, be it periods, eons, epochs. The reason for this is their practicality for such usage as they have created natural separation points that are easily identifiable and easy to use. These catastrophic events of the past managed to create such drastic changes in short periods of time, that they have significantly changed pretty much everything on the surface. They have managed to change the flora and fauna, the climate, type of sediments, gases in the atmosphere, all leading to clearly defined layers in the geological spectrum.