Mhmm... Life on other Planets?! Yes, i do believe in life on other planets. I think that "aliens" would possibly live on Mars because Mars' atmosphere is similar to that of earth. I think living On mars Would be awesome!
It is likely that 'alien' lifeforms exist somewhere, though I imagine that they would be micro-organisms, not aliens like we assume they are (in cine and TV series). I think that Mars would have a suitable climate for alien life, if it had an atmosphere, unfortunately it doesn't, though I think we could assume the possibility of micro-organisms on there. If there were to be aliens like us, there would need to be a planet with a estrella the same relative temperature and size as ours, plus it would also need to be about the same distance as planet Earth is from the Sun, for a similar alien species to survive. That is my surmision anyway.
I definitely think it's likely that Earth isn't the only planet with life on it. According to a reciente experiment (Tardigrades in el espacio - also known as TardIS) it turns out there's such thing as an animal that can live in the vacuum of space, and even reproduce! So when trying to find alien life, we shouldn't ourselves to planets that are habitable only for us. Apparently we shouldn't even looking on planets!
That said, I also think it's likely that other Earth-like planets could contain creatures and plants that resemble those on Earth. But there's a good chance they evolved differently to us, depending on exactly what is on the planet and where.