You are presented with the quiz "Prehistoric life is preserved in rock when what covers the remains over time?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "fossils are formed when layers of sediment cover the remains of organisms over time" and "fossils are evidence of prehistoric life that is preserved in rock". 

So, what's the best answer to the question?


 

   layers of sediment        