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Comment by acconrad | Hacker News Reader

> However, many scientists believe Mars was much warmer and wetter billions of years ago, when it may have had a thicker atmosphere to help trap heat.

This is both fascinating and horrifying. Given the timeline of the solar system thus far, it would seem plausible that an entire evolution of species, including the rise and demise of intelligent life, could have already started and finished on Mars.

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Taking this one step further, it is also possible that life has been exchanged between our two worlds. Large meteor collisions in the past have moved parts of Mars to Earth, and possibly also Earth to Mars. And some small life can exist clung to rocks in space (we know of such creatures here on Earth)! So perhaps, Mars was once wet and warm and full of life. Perhaps it suffered a large impact of some kind billions of years ago, and perhaps that impact flung Mars rocks with little tiny Martians on them towards Earth. In fact, this could have happened thousands of times.

It's possible, anyway. You know, while we're speculating.

Yep, it's called Panspermia: http://en.wikipedia.org/wiki/Panspermia

It's a pitty we are not digging in the underground of the planet yet; imagine the amount of fossils and history one could find if the planet had been habitated before.

I don't understand why that would be horrifying?

Terra forming Mars has never been something which I imagined we would do. I always thought we'd be living in greenhouses and digging for minerals and fossils.

The Long Mars (by Pratchett/Baxter) explores some ideas like that on a trip through parallel universes, though it's 3 books into a series that doesn't lend itself to skipping around.

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