Question

Human civilization, at least since the time of ancient Egypt, is on the order of 5000 years old. The age of the Earth is on the order of 5 billion years. Suppose we use the length of a football field, or about 100 meters, as a timeline to represent the age of the Earth. If we put the birth of the Earth at the start of the timeline, how far from the start of that line would human civilization be?

Answer 1

Write and solve an equation of ratios:

5 *10^9 years 100 m
------------------- = --------------
5 * 10^3 yrs x

Reducing the first fraction,

100 m
10^6 = ----------
x
100 m
Solving for x, x = ------------- = 10^(-4) m, or [10^(-1)] * [10^(-3))]
10^6
this comes out to one tenth of 1 millimeter.