Answer:
If the duration of life on Earth was on a scale of 20,000 days, the human species would be present in the Earth for approximately 9 days.
Step-by-step explanation:
We can't be sure about the exactly age of the Earth, but we can base our calculus in a number between 4400 and 4600 million years, because the most accepted researches shows numbers in this span of time. We can take the average of those limits: 4500 million years.
On another hand the presence in the Earth of human species has not a precise date because of the it does not have a precise date for two main reasons, the scientific evidence does not include all the human species that existed on Earth but it is a very incomplete evidence and besides being an evolutionary phenomenon it is not easy to determine from what moment We can consider that a species belongs to the human race or not. In any case, we take the approximate date of the scientific evidence of the existence of human species in an age of 2 million years.
With both numbers we can calculate the proportion in the scale of 20 thousand years throw the following formula:
PHS = 20000 years . 2 million years / 4500 million years = 8.9 years
PHS: Presence of Human Species