For those who are wondering before reading - article looks at the issue of what is considered a "highly likely" indication in an alien planet's atmosphere that would indicate life. Oxygen used to be considered that, but other processes have been found that can lead to significant O2 without life.
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Thanks for the TL;DR. I find these magazine-style articles that start with waffle instead of the conclusion very frustrating!
> I find these magazine-style articles that start with waffle instead of the conclusion very frustrating!
Imagine there was a rule that popular-press science articles were required to have an abstract that candidly summarized the article:
Title: "Is there life elsewhere in the universe?"
Abstract: "We have no idea, and this article doesn't change the status quo."
How about life without oxygen? I always wonder why alien life or any other life cannot happen without it.
> How about life without oxygen?
It's thought that life began here in the absence of oxygen, and only over time did oxygen begin to play a part in cellular life. As another poster points out, there are still some cellular organisms here that do without oxygen, indeed they would find it toxic.
> I always wonder why alien life or any other life cannot happen without it.
But that's not true, not even here. Oxygen is regarded as a sign of life, but its absence doesn't suggest the absence of life, only the kind of life that requires it.
> How about life without oxygen? I always wonder why alien life or any other life cannot happen without it.
If by oxygen you mean molecular oxygen, O2 -- rather than atomic oxygen as part of some other compound -- we know life can happen without it, since there is life on earth that lives without it. And, IIRC, we have strong reason to believe that life that could live without O2 predates life that needs O2, and, in fact, it is life that made free O2 available, not free O2 that made life possible.
> And, IIRC, we have strong reason to believe that life that could live without O2 predates life that needs O2, and, in fact, it is life that made free O2 available, not free O2 that made life possible.
Yes, early life on Earth was all anaerobic. That started around 4.1 Gya (billion years ago)[1]. The Great Oxygenation Event[2] happened around 2.3 Gya - that wasn't the first appearance of photosynthesis, but it was the point at which it changed the atmosphere enough to wipe out most of the other life on Earth at the time. Obligate aerobes - organisms that need oxygen to survive - were later still.
[1] https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h...
There is already life on earth without oxygen. Deep sea bacteria lives on sulphur and carbon dioxide.
I think this is finally being considered. Just because we're carbon based doesn't mean all life must be.
There a good reasons for organic chemistry being the main one. Carbon is abundant and can be combined in numerous ways to make complex molecules and stable ones at that. There are very few other elements in the periodic table that can hope to offer similar properties. So carbon based life is not just a guess, its a high probability.
I don't know where this myth comes from that scientists have some sort of strong belief that no other form of life is possible, but it's not true. What we have is a lot of ignorance, so many scientists will often concentrate only on those forms of life (plural) we know exist because we share a planet with them, because those are the forms of life we can actually discuss with confidence, but I doubt you can find a serious scientist who will confidently proclaim no alternatives are possible.
There are good reasons to believe that ours is quite likely and good reason to be skeptical of alternatives, in the proper scientific sense, but certainly not disproved or something.
> I doubt you can find a serious scientist who will confidently proclaim no alternatives are possible.
Undoubtedly. The problem is that very few people, even among the well-educated and technically proficient, actually form their views about the state of science by talking to scientists.
Well eventually, oxygen et al will just be catalysts to silicon based life :)