There is a theory called the "Goldilocks" theory that explains why 
Earth was just right. Just as Goldilocks found the porridge that was 
just right, the Earth seems to be just right for living creatures. 
The Earth seems to be the perfect distance from the sun for lots of 
water. 

Venus is too close to the sun, and too hot for flowing water on it's 
surface. In fact, it is so hot that, like a sauna, all the water has 
been evaporated into the atmosphere, and Venus has a thick and heavy 
atmosphere. 

Mars is too far from the sun, and too cold for flowing water on it's 
surface. Mars also has no continental drift, so particles of the 
atmosphere which become trapped within the ground stay trapped within 
the ground. Thus over time the atmosphere of Mars has become thin, 
and all the water is frozen into the ground. 

The temperature of Earth is just right for flowing water on the surface, 
and for the rock which allows for continental drift. With continental 
drift, particles of the atmosphere which become trapped within the 
ground are brought back to the atmosphere through eruptions of volcanoes. 
These conditions cause refreshment of the planet's atmosphere. A medium 
sized atmosphere helps keep temperatures just right for flowing water 
(through the greenhouse effect). These conditions are just right for 
abundant life.

As for coming from the Earth, I concur. I dont' pretend to say that aliens 
put us here, or we came from Mars. We were created on this planet, from 
this planet. the favorable living conditions paved the way for the creation 
of the first living cells, from amino acids (inorganic matter) to organic
matter. Last time I checked I wasn't made of clay though!