[Marko]

Originally Posted by AntonioLao

If I'm not mistaken, all life forms share the same base pairs of DNA molecules but not the way they combined or the number of molecules involved in the combinations.

Yes, they share the same base pairs; combinations are the one that give rise to the species we see today.
That is like this on Earth, but my speculation is that on "primordial Earth" there could have been other reactions that were not so successful, and perhaps other building blocks were there. But by accidents, these building blocks we see today were probably most stable and successful, and we are here today to discuss this topic. What I wanted to say is that our particular evolution is with 4 bases, but there could be other "evolutions" based on different building blocks and chemistry on other planets.
Regards!