Why do scientist use mass extinction to separate one era from another

What are some natural resources found in midwest

The distance a car travels between the time the driver decides to stop the car and the time the driver puts on brakes is called the reaction distance. how does the reaction distance change with speed? a. reaction distance decreases with with speed b. reaction distance stays the same with speed c. reaction distance increases with speed. d. there is not enough information to answer the question

Why might a geographer choose to present information in a map rather than with stactics or in me asap