These fossils are very useful for us because we can use them to date the layers of rock that they are found in. Fossils that can be used in this way are called index fossils, and rock layers with the same index fossils in them can be correlated. Not my answer, link here for full
http://peter-mulroy.squarespace.com/correlating-rock-layers/
Answer: What roses are the best flowers is a non-scientific question.
Explanation: What flower is better is determined by personal opinion. I might think the red roses are prettier and you might think the white ones are. Where all the other questions can be tested all equally and it is not an opinion.
