What is it that worms do to make soil more fertile?

Question

If worms make soil more fertile, how do they do it?

Answer 1

Earthworms...

... break up the soil making it softer and easier for roots to spread, and allow oxygen (air) to circulate
... they eat leafs, grass, etc and they digest it out with more nutrients than when it went in
... they multiple quickly making it easier to do the first two more often.