| A | B |
|---|
| fossil | a preserved clue to life on Earth long ago |
| trace fossil | fossils that show changes that long dead animals made in their surroundings |
| mold | a fossil imprint made by the outside of a dead plant or animal |
| cast | a fossil formed when sediments or minerals fill a mold |
| fossil fuel | fuel formed from the remains of organisms sthat lived long ago |
| petroleum | a thick brown or black liquid fossil fuel; fuel that is mainly used in transportation |
| natural gas | a gas, mostly methane usually found with petroleum |
| peat | a soft brown material made up of partly decayed plants; first stage of coal formation |
| lignite | a soft brown rock; the second stage of coal formation |
| bituminous coal | a fairly hard. dark or black rock; the third stage of coal formation |
| anthracite | a hard black rock; the fourth stage of coal formation |
