How many millions/billions of years do you think Asteroids have been hitting Earth? Right this very instant Space Dust from outer Space is settling DOWN on the land and Oceans, on your house tops, the tops of your cars/everywhere. You think that air out there is 100 percent pure and clean? it is NOT! Step outside, look at that Space coming Down from millions/billions of Light Years away. Earth is made of Space Junk! Whatshisname ///Carl Sagan, WOO WOO WOOF!/// once said we are made of Star Stuff, and he is right too.