Our Solar System is moving...It was estimated that the Solar System takes a million years or so..to travel through this spiral arm.
Millions of years from now..Our Solar System will not be where it is today.

The point being..we are in a part of space right now, that is relatively vacant. A million years from now, Earth, and the rest of our solar system may be in a very busy part of this spiral arm. I read somewhere we are headed towards the Aquila Rift(sp?)

Our System, could have been in a very busy part of the spiral arm which may have extinguished dinosaurs.

And we may have passed planets with life..(you don't suppose our ancestors jumped onto our planet..from another one?..(I don't really believe that..but?..hehe:)