Preserve the environment.
Maybe that's it. Not quite sure
Not as old as those found in deeper layers
I believe that the answer is c. Humans can affect the physical environment by not upkeeping it. Also the physical environment can affect humans, for example, too much pollution can result in a sickness
Rivers, because it has a constant flow from other water sources so that means it could just flow right in
Its composition resembles that of the sun, it differs from a star in that nuclear fusion doesn't occur at its core.