Step 1: 
An animal dies. The animal’s body sinks to the bottom of the water. The soft parts of the animal’s body rot away. Only the bones and teeth are left. The skeleton is slowly buried by sediment.

Step 2:
More and more layers of sediment build up over the skeleton. The weight of these layers turns the sediment to rock. This takes thousands of years.

Step 3: 
Water slowly dissolves the bones of the animal’s skeleton. This leaves a hole or cavity in the rock that is the same shape as the skeleton.

Step 4: 
Minerals in the water slowly build up inside the hole. Eventually, these minerals fill the hole, making the same shape as the skeleton. A fossil has been formed.

Step 5: 
How do people find fossil’s on Earth’s surface if fossils form deep underground? Natural events such as an earthquake or the making of mountains push the fossil up to the surface. Over time, wind and water wear away the rock. The fossil is now visible.

• Fossils are formed in sedimentary rock. Layers of sediment make up sedimentary rock. These same layers bury a skeleton so it can become a fossil.
• The oldest known fossils were formed about 3.5 billion years ago.
• Plants can also become fossils.
• Fossils tell us about animals that became extinct a long time ago.
• Some fossils show traces that animals left behind. Eggs, nests, footprints, and even animal droppings can become fossils.