They are used to define periods Geological time.
Answer:
I would say it is B.
Explanation:
In Meiosis, specifically in Prophase 1, it creates genetic variation. Crossing over occurs in that stage
1.It is not natural.
2.It can came up with side effects and unbalance some species.
Earthquakes only occur at transfer boundaries where two tectonic plates will slide or rub past each other.
If there are no boundaries in mid-America, then earthquakes are not possible.