It is difficult for humans, whose lives are measured in years and decades, to fathom the age of the Earth, whose history is patiently but inexorably written on thin pages of landscape, each lasting millions of years or more. As an exercise in Earth-time, let a single mile represent a million years. Thus .5 mile would represent 500,000 years, .10 mile equals 100,000 years, .01 mile (52 feet) equals 10,000 years; .001 mile (5.2 feet) equals 1,000 years, and about 6 inches equal 100 years. A decade would equal about half an inch. It is 450 miles from the 60th Street on-ramp on Interstate 80 in downtown Omaha to the westernmost 1-80 exit at the Wyoming border, which may be thought of as equal to 450 million years. This period of nearly half a billion years encompasses most of the time that evidence of animal life has been found on Earth, but Earth itself is more than 4 billion years old, or ten times older than the time scale described here, and the earliest known algal fossils are 3.8 billion years old. To start at the approximate age of the planet Earth, we would have to travel about 4,500 miles, rather than 450 miles, to get a sense ofthe time involved. The age of the universe is perhaps three or four times greater, or more than half the distance around the globe at Nebraska's latitude, at the rate of 1 mile per 1 million years.
Available at: http://works.bepress.com/paul_johnsgard/284/