Sidebar - July 2006
by Do-While Jones

The Great Wall of BBs

Visualizing Large Numbers

When we talk about “billions”, “trillions”, and "parts per million", it is sometimes hard to really comprehend them. When thinking about the composition of the atmosphere, it might help to imagine a great wall all the way across the United States, 3,000 miles long, 8 feet high and 75 feet thick, built entirely of BB shot.

You have probably seen a BB gun, and know how little a BB is. A BB is 0.177 inches in diameter. That’s less than a fifth of an inch, (or 4.5 millimeters for our non-US readers). Let’s pretend a molecule of gas is the size of a BB.

A typical residential street in the western United States is about 75 feet (about 23 meters) from curb to curb, which makes it wide enough for two lanes of traffic even if there are cars parked on both sides of the street. Streets in the eastern United States are sometimes narrower in cities that were built before automobiles were prevalent, so you may have to adjust your imagination if you live where streets are narrower.

If a street is 75 feet wide, it would take a row of 5085 BBs to stretch from curb to curb. So, one thousand BBs would only stretch 1/5 of the way across the street.

Homes in the United States typically have 8 foot ceilings. It would take 542 BBs stacked on top of each other to make a column 8 feet high.

So, if one wanted to build a section of a wall of BBs, 8 feet high across a 75 foot wide street, it would take 2,756,070 BBs. That is, it takes almost 3 million BBs to build that wall just one BB long.

If one had one billion BBs (in the United States, one billion is a thousand times a million) one could build a wall 8 feet high, 75 feet thick, 5.3 feet long.

A trillion BBs (that is, one thousand times a U.S. billion) would allow one to build that wall 5300 feet long. That’s just over a U.S. statute mile (5280 feet). If you prefer to think in metric units, one could build a wall roughly 20 meters wide, about 3 meters tall, and about 1.6 kilometers long out of one trillion BBs.

Let’s suppose one BB represents one carbon 14 atom in the atmosphere. Then the number of carbon 12 BBs in the atmosphere would be the number of BBs in a wall as high as your ceiling, as thick as a residential street, one mile long.

If carbon dioxide represents 0.033% of all the gas in the atmosphere, and argon makes up 1%, then a wall of BBs 30 miles long would represent the number of argon atoms in the atmosphere. Since the atmosphere is about 20% oxygen, a wall of BBs representing oxygen molecules would be 600 miles long. The 80% of the atmosphere containing nitrogen would be represented by a wall 2400 miles long.

So, try to imagine a wall of BBs as high as your ceiling (8 feet high), as thick as a residential street (75 feet thick), stretching from the east coast of the US to the west coast (3,000 miles). 2,400 miles of that wall represents the amount of nitrogen, 600 miles represents the amount of oxygen, 30 miles represents the amount of argon, 1 mile represents the amount of carbon 12, and a single BB represents the amount of carbon 14 in the atmosphere.