They have been correlated with meteor impacts, major and sudden drops in sea levels, intense vulcanism, and migration of the continents due to plate movements. Some extinctions may even be related to the release of cosmic rays from exploding stars and to influx of cosmic rays during a reversal of the Earth's magnetic field. It is fairly clear that the ebb and flow of life on Earth is tied to little understood cosmic and Earth-borne processes that precipitate violent ecological change. Wave upon wave of life forms have lapped at the Earth's shores and risen and fallen in the seas and skies. The succession of one life form over another is a recurrent theme in the Earth's history.
Evolutionary replacement requires no conscious thought.
It is simply the result of natural selection. The ecosphere is alive and life changes the ecosphere. Symbioses knit together the fabric of life so that each action, each event, ripples through the fabric. The reproductive strategy followed by species, according to current theory, is to produce the most offspring, either sexually or asexually, that can survive to repeat the cycle and thus carry on the genetic story. No thought is given to how this will change the Earth or affect other creatures.