What is it that's everywhere but often unnoticed?

Answer: Air.

Yes, air.

You might think water, and you'd have a good argument. Three-fourths (75%) of the earth is covered by water, after all. Plus, water is relatively simple stuff. Duct tape a couple of hydrogen atoms together with an oxygen atom, and before you know it, you're all wet.

But despite our abundance of water, we don't spend much time in it. Or thinking about it. A quick shower, the occasional swim, the odd rainstorm pretty well sums it up. Most of the time, then, we're entirely immersed in air.

For being so completely enveloping, we rarely notice it. At sea level the massive weight of the whole atmosphere is pressing down with about 14 1/2 pounds of pressure per square inch. But since we were born in it, we don't notice it. Air is more complex than water, too. Forget the duct tape; for air, you're going to need some nitrogen and oxygen, mix them about 4 to 1, add a dash of water vapor and other gasses, then — breathe.

Continued...