What evidence do scientists have that Earth has been hit by large objects, like asteroids, in the past? Check all that apply. layer of volcanic ash
layer of burned organic matter
change in average global temperature
mass extinctions
earthquake activity

What is point source pollution of an aquatic ecosystem? a) pollution of freshwater sources b) pollution from many sources that combine into one c) pollution that occurs over a wide area; water that runs off from fields, parking lots, and other land surfaces d) pollution that can easily be identified with a single discharge source, such as an open pipe which drains into a body of water