http://en.wikipedia.org/wiki/Plate_tectonics
Continuing, it turns out that our spiral galaxy is a perfect shape. Elliptical galaxies often do not have enough heavy elements. Neither do globular clusters, which also have hot and colliding stars.
Our galaxy is also a perfect size, since smaller ones often lack the heavy elements.
Our Sun has a perfect location in our galaxy. In the center there would be too many collisions. On the edges there are frequently not enough heavy elements.
The large planets in our solar system fortunately did not spiral into the Sun or outer space, taking Earth with them, as is often the case. In fact, the planets, including Earth, all have relatively stable orbits.
Additionally, our sister planet, Jupiter, runs interference for us by clearing out many comets and asteroids.
Our Sun is the right size to last a long time, which is great for evolving complex life. At 5 billion years, our Sun is halfway through its life.
Next Page 1 | 2 | 3 | 4 | 5 | 6
(Note: You can view every article as one long page if you sign up as an Advocate Member, or higher).