What caused the greatest increase in diversity of life during the course of evolution?

the main factor for the increase of diversity is the environment. in many areas of the world the environment changes rapidly, and because of this animals have to adapt quickly, sometimes change in behaviour. so many animals evolve into something new that will benefit them more in that environment, take finches for example (theory of Charles Darwin), many finches evolved to have different beaks to suit the food they were provided with in the area (Galapagos Islands). in some cases animals permanently move from their normal habitat to a new one where the environment is more suitable for them. and that's why there is a diversity in animals.