"Coal's a fossil fuel, just like gas. Mrs. Lee told us all about it once. She said that coal was formed after prehistoric plants, like tree branches, died and rotted. They were crushed under rocks and dirt and over time the pressure and heat of the Earth slowly turned them into coal and other fossil fuels."

"That's why we have to conserve energy," Courtney added. "It took millions and millions of years to get the coal and gas and oil we have now. If we use the fossil fuels too fast, we'll use everything up."

Collin laughed. "Guess I can't escape Mrs. Lee and her science lessons even when I'm stuck in the middle of nowhere."

Morgan and Courtney laughed, too, but the merriment stopped when a flaming ball whizzed through the void and crashed into another puzzle piece, opening one more portal for the kids to explore.

One down, seven to go, the whispering voice laughed. Hurry! Hurry!

Collin blew out a gust of air. "Are you ready to go again?" he asked Morgan and Courtney.

The girls shook their heads. Morgan had no desire to begin another adventure. One was more than enough. She'd fought off a dinosaur, almost been swallowed by thick, stinky ooze, and she was still miserable, stinky and covered with goo. She wanted to go home -- but the only way to get there was to find seven more puzzle pieces.

"Okay. I'm ready," she reluctantly said.

Courtney laughed. "Me, too, I suppose."