Tuesday

At the natural history museum, Raven stops at a lump of shiny black coal. Next to it is a fossil fern pressed into rock.

"They are right next to each other," she says. "What do you notice that they have in common?"

Rocket squints at the fern. "Plants? Coal is made of plants?"

Nova hovers by the sign. "Would you like a hint?" she asks. "Read how long ago those plants were alive. Then think about what happened to them."

Coal, oil and natural gas are called fossil fuels. They formed from living things from long ago.

Coal holds energy stored by plants that lived hundreds of millions of years ago in swampy forests.

Over millions of years, layers of dirt and rock covered those plants. Pressure and heat slowly turned them into coal.

Oil and natural gas formed from tiny sea plants and animals. They were buried on the ocean floor under sand and mud.

Because fossil fuels take so long to form, they are nonrenewable. Once we use them, they are gone for a very long time.

There are three main fossil fuels: coal, oil and natural gas.

Coal came from plants in swampy forests. Oil and natural gas came from tiny sea plants and animals.

All three were buried and changed by pressure and heat over millions of years.

Nature cannot make more fast enough to replace what we use.

You traveled back millions of years today! Tomorrow you play a game that shows why running out matters.