What percent of the history of life on Earth have humans existed?
somewhere between 0.13% and 0.2%
We don't have exact dates for things that happen on geological scales. Our best guesses are that life began somewhere between 3.5 Billion and 3.8 Billion years ago and as far as humans are concerned, our estimates range between 5 and 7 Million years ago. So, dividing the estimates by each other we get that:
So there is the range of estimates that humans have existed in comparison to life on Earth.