Why and how earth has gravity?

Matter attracts other matter. The Earth, Us, and 99.99999999% of everything near the Earth is made of matter. We call this attraction gravity. That's about all there is to it.

So, really, then, all females ARE attracted to me? Awesome!

Seriously, though, what are some hypotheses on why matter attracts matter?

There is some interesting information concerning gravity on the following site.

Howstuffworks "How does gravity work?"

There aren't really many hypotheses. It's a complete mystery. But we can model it very well indeed which is the important thing.

At its heart all of physics is a big mystery. Why do bodies attract according to the product of their masses and the inverse square of their distance? No one knows. Why does F=ma, or E=mC^2? Why is energy conserved? Why does entropy increase? No one knows why any of this. All scientists can really do is continue to come up with more fundamental theories that do an ever improving job of predicting how things behave, not why they behave thusly. When scientists get into the realm of "why," things can get awfully muddled. I'm thinking particularly of the anthropomorphic principle, which has gained some adherents in certain quarters - some would maintain that the reason gravity works as it does is because if it didn't none of us would be around to ask the question "how does gravity work."