It would be very difficult to date geology if the evolution of life had been proceeding steadily without any setbacks or special opportunities  It's easy to tell geological time because geologists call it Faunal succession,when species suddenly appear or disappear, we can think of these events as a threshold of time, a moment, a period, usually representing a climate, giving way to a new period, a new climate  Only three variables are strong enough to turn on the clock of continental drift, galaxy collisions, and the dynamics of climate change, such as greenhouse gases  All these factors operate in different ways, but they act in the same way to drive evolution
Death and opportunity
Faunal succession is the main basis for the division of geological age.