extremophile microbes live deep in caves, and can be found as far as 1,000 feet below the surface. These microbes do not depend on the Sun for energy. Instead they use gases and non-organic materials that would kill you and I.

Life is all around us. From many kilometers (miles) into the atmosphere, to many meters (feet) beneath the surface of the Earth, life is everywhere. What is this stuff we call life? What are some things that all life forms have in common?

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Living Things Are Made of Cells All living things are made up of cells. These cells are the basic building blocks of life. As an example, have you ever seen a sand castle? At a distance, the sand castle looks like a smooth brown building. As you get closer to the sand castle, you can begin to see that it is not one smooth building, but instead that it is made up of millions of tiny grains of sand.

Looking at an elephant, you might see what looks like a smooth gray animal. And it is true that this is what you are seeing. However, just like the sand castle, if you could get close enough, and if your eyes were powerful enough, you would realize that what looks like a smooth gray surface, is really made up of many billions of smaller objects called cells.

Cells are tiny units of living materials separated by a cellular wall, or barrier. These cells are so small, that they can only be seen with a powerful tool known as a microscope. Cells make up every part of a living thing. Your skin, your hair, fingernails, blood, bones, nerves, and muscles are all made up of cells. These cells work together to keep the life form alive.