Today is Earth Day. And you should take the stairs. Not because it's saves a lot of energy. If you take two flights of stairs every day at work, you'll save 72 kilowatts of energy on each day, which saves 90 cents a year in energy costs. You should take the stairs for two other reasons.

One, it's a green thing to do, says Renee Mullen of The Nature Conservancy's Conservation Science Group. And any energy saved is good for the environment.

Two, it's a healthy thing to do. It's good for your body to move. It's good for your head too. So today, take the stairs. Do it every day if you can. But at minimum, do it today.