Fossils are formed when layers of sediment cover the remains of organisms over time.
Natural gas is a fossil fuel.
Natural gas is formed from layers of sediment covering the remains of organisms over time.
What is formed from layers of sediment covering the remains of organisms over time?
Options:
  - metal
  - cold
  - rings
  - coral reef
  - sea urchins
  - natural gas
  - exoskeleton
  - shells