
It's been considered for a long time, that they brought both water and life, I suppose both are mutually compatible. It's extremely likely there was life on Mars at some point.
Obviously we're a long way from proving these things, but science is science, if these elements are 'alien' because of the time scales then it is what it is. Earth is full of material coming in from space, we know this for a fact, and the inner solar system is far less turbulent now than it was.