Answer:
2
Explanation:
valence electrons=reaction
The answer is the first one A
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/
Seismic activity, weather, erosion, and mishandling are a couple. Need anymore let me know
