A trilobite fossil from the Cambrian , 500 million years old, from the Burgess shales in Canada.
The Cambrian explosion is amazing, billions of years of single cell bacteria, then complex life in a bare 20 million years or so. Latest theory is that oxygen levels had just risen to the point where complex animals were viable : then both sex and predation appeared, which massively accelerated the rate of evolution.
Pessimism is the soft option.