How life exist on the earth?
Our solar system is spinning:
So the planets,meteoroids,comets,meteors,meteorites and asteroids makes circles around the sun(star),and the meteoroids,comets,meteors,meteorites and asteroids are hitting together,and they form a planet.
Every meteoroid,comet,meteor,meteorite or asteroid could contain special minerals like microorganism.
This microorganism could contain good things and bad things,the microorganism which was in the asteroid,which killed all dinosaurs on the earth was a good thing.
The good thing was that this microorganism was something,that allowed the planet earth to create new life,which created us.
This is how life exist on the earth.
Btw. here is the difference between meteoroids,comets,meteors,meteorites and asteroids:
P.S the bad thing could be a microorganism which contains an aggressive virus like ebola,HIV and others.
We basically have all HIV in us,which is waiting for us to do something dumb.
Its basically like in the series of The Walking Dead,the virus is already in u,but it waits for u to die.