Eternity is the length of time it would take an ant to move the Sahara desert to the moon one grain at a time.

I don't know who thought of this analogy, but I've always wanted to do the calculations. After a little research on the internet for the raw data the fun begins.

8,500,000 grains of sand in one cubic inch
780 inches average depth
3,400,000 square mile area (sandy area only)
one inch per second average speed of an ant
239,000 miles to the moon

8,500,000 X 780 = grains per square inch = 6,630,000,000
X 144 = grains per square foot = 954,720,000,000
X 27,878,400 = grains per square mile = 26,616,066,048,000,000,000
X 3,400,000 = grains per Sahara desert = 90,494,624,563,200,000,000,000,000

12 X 5,280 = inches per mile = 63,360
X 239,000 = inches to the moon = 15,143,040,000
X 2 = round trip to the moon in inches and seconds = 30,286,080,000
divide by 3,600 = hours per round trip = 8,412,800
divide by 8,766 = years per round trip = 959.7

90,494,624,563,200,000,000,000,000 X 959.7 = eternity =

86,847,690,093,303,040,000,000,000,000 years

This number reads as follows:
Eighty six octillion eight hundred forty seven septillion six hundred ninty sexillion ninty three quintillion three hundred three quadrillion and forty trillion.

That's 6,680,591,545,638,695,384 times the age of the known universe.