Yesterday, I talked about why we should look for a history of life on Mars, and had an article for SEED magazine to that effect. After all, we’ve made some recent geological finds that are surefire indicators of past liquid water on Mars, and possible indicators of past life.
While most of the article was about Mars’ history as a planet and the argument that in the past, it was much more Earth-like than it is today, I had one sentence that appears to have touched off a firestorm in the comments:
I don’t know whether there was life on Mars or not, but based on what I know about abiogenesis and early Martian conditions, I think there’s a good chance there once was.
Abiogenesis, the process and theory of life arising from non-life, is a very touchy issue for a lot of people, and it isn’t my specialty. So what am I doing talking about it?
Because this is a fundamental assumption that we make about the natural world. In all instances that we’ve observed, life only originates from pre-existing life. Yet at some point, there was certainly no life. It’s hard to imagine having life when your Universe is so hot you can’t even form atoms, isn’t it? So if we go back 13.7 billion years, close to the big bang, we know there was no life.
So there are a whole plethora of possibilities for its origin. The primordial soup on Earth, in the atmosphere, in space, on another planet, from a pre-existing star, etc. Abiogenesis is simply the idea that when life arose, it did so from non-life, through natural processes.
We have no idea how long it took (the oldest evidence for life on Earth points back at least 3.5 billion years), whether Earth started with life or not, or whether that life originated somewhere else. But we know that we have life now, and we know that at some point in the past, there wasn’t life in the Universe. So yes, I’ve made an assumption of abiogenesis. But is that unreasonable? Other than life originating supernaturally, is there any alternative? I suppose you could say it was brought here from another Universe, but then it had to originate in that Universe somehow. Unless it’s turtles all the way down, I don’t see it.
And as scientists, we operate under the assumption that the laws of nature govern the observable phenomena in the Universe. Including the origin of life. So this is an open scientific question, as to how life originated. That’s why people still study it. We can get to complex organic molecules from non-life, and we can get to a huge amount of complexity starting with simple life, but we don’t know how to go from complex organic molecules to life, yet. But I think it’s reasonable to assume that we must. Do you?