Alien ancestors?

Visualize this -- Two planets collide and the debris ejected into space contains fragments that are rich with organic material.  The fragments themselves become meteorlike bodies that traverse space until they land on other planets.  Within a landing meteoroid is viable life substance that has been nurtured by radioactive heat source(s) and nutrients.

Voila!  New amino acids and nucleobases take root and possibly flourish far from their origin.

From the TIME article by Jeffrey Kluger, titled Aliens Among Us (you need a subscription to read the whole article):

Life, as far as we can prove, exists only on Earth. There is our modest planet circling our modest star, and then there is the unimaginable hugeness beyond. Yet in that whole, great cosmic sweep, we're the only little koi pond in which anything is stirring. That, at least, has been the limit of our science. But that limit is changing fast.

The cosmos, as scientists now know, is awash in the stuff of biology. Water molecules drift everywhere in interstellar space. Hydrogen, carbon, methane, amino acids--the entire organic-chemistry set--swirl through star systems and dust planets and moons. In 2009, NASA's Stardust mission found the amino acid glycine in the comet Wild 2. In 2003, radio telescopes spotted glycine in regions of star formation within the Milky Way. And meteors that landed on Earth have been found to contain amino acids, nucleobases--which help form DNA and RNA--and even sugars.

The study that looks at "the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids and planetoids" is called panspermia.  There's an interesting site on the topic called Panspermia-Theory, "origin of life on Earth."  There's also a Panspermia.org, that states "Life comes from space because life comes from life."  Not sure about that, but it could be an interesting stop.

If you're scientifically inclined, be prepared to be fascinated by this video, uploaded by Gravitionalist:

-- Marge