Choose your answer from: 1. metal 2. cold 3. rings 4. coral reef 5. sea urchins 6. natural gas 7. exoskeleton 8. shells

Fact 1: Fossils are formed when layers of sediment cover the remains of organisms over time. Fact 2: Natural gas is a fossil fuel. Given the two facts above, what is formed from layers of sediment covering the remains of organisms over time?
Answer:
6.