Why does the layer of humus form quickly in a rainforest?

The point where two air masses meet is called a

If we represent the solar system on a scale that allows us to walk from the sun to pluto in a few minutes, then a) the planets are microscopic and the stars are millions of miles away. b) the planets are the size of basketballs and the nearest stars are a few miles away. c) the planets are marble size or smaller and the nearest stars are thousands of miles away.

Can someone me with this plz? ! i'm putting 20 points on it!