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Comment by speeq | Hacker News Reader

> “Wait a second,” he said. “How do you know we’re the only time there’s been a civilization on our own planet?”

Imagine for a moment that we're Martians who managed to terraform Earth because of some runaway climate catastrophe on Mars. That now, we're in the early stages of repeating the same mistakes because of some extinction event in the past that wiped out all of our prior history and knowledge.

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If they could terraform another planet, they could probably just fix mars instead. There are a lot of weird contradictions in these kind of stories. Like they can move an entire planet's worth of people, but can't make a data repository that would survive them. Or that they would have a bad climate on mars, but somehow survive long enough to learn how to terraform a whole planet reliably as well as cross solar-system level distances.

> If they could terraform another planet, they could probably just fix mars instead.

So why do humans find it easier to conceive of terraforming Mars, than to just fix our planet instead?

Terraforming Mars is more adventurous and romantic.

It's the same reason that software engineers love greenfielding projects. Architecting clean, fresh systems is romantic! You won't make any of the mistakes that you've now learned from! All this needless complexity can be done away with once and for all.

We're too similar to other life on earth for that to be credible.

We says we, the martians, didn't bring the other stuff with us?

Life has been on Earth for at least 3.8 billion years. All of the life on Earth today is descended from that original life. So if life on Earth originally came from Mars, it would have had to do so at least 3.8 billion years ago. But that's too close to the origin of the solar system as a whole for it to be credible that an industrial civilization could have evolved on Mars, caused a climate catastrophe, and then migrated to Earth.

I don't think it's at all likely that life on Earth originated on Mars, but if it did then there could have been cross pollination of microorganisms over billions of years due to meteor impacts on both worlds throwing bits of crust into space. In fact if we do find life on Mars at some point it wouldn't be shocking if they are quite similar to bacteria found on Earth, since they might just be descendants of earth bacteria carried over from the impact that killed the dinosaurs.

Or ok the flip side perhaps life originated on mars or europa or even interstellar, with single cells organisms coming from there

> if it did then there could have been cross pollination of microorganisms over billions of years

I don't think this is consistent with DNA evidence, since such cross pollination would be expected to show up as two sets of genetic lines of descent with very different characteristics, since the environment of Mars is very different from that of Earth; and we don't observer anything like that. In fact, if life was evolving separately on Earth and Mars, it might not take very long before the two lines of descent were not even compatible genetically, meaning that genetic exchange would be impossible even if the organisms were brought back together.

I just thought of that that argument only holds water if there wasn't exchange of genetic information between the planets. If during evolution cells and viruses get blasted from one planet to the other on a regular basis, that would not be a great argument.

It would have had to have been going on long before intelligence arose though, which is not impossible.

Venus makes much more sense in the comparison,

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