Geological clock with events and periods.
To put into perspective the time it took for complex life to evolve, the time since the formation of the Earth (around 4.5 billion years ago) is represented as the twelve hours of a clock.
If the Earth formed at midday, animals first evolved just before 10pm, the first mammals just after 11pm and the first humans around twenty seconds before midnight.
This is not to suggest that there was nothing before the Earth (the universe exploded into being 13.7 billion years ago) or that time is anyway cyclical; it is only meant to demonstrate the scale of geological time. Nor is it meant to indicate that the evolution of humans is some endpoint to which evolution was aiming.
