Life as we know it needs water, but life as we don't know it may run on concentrated sulfuric acid. The chemistry of life as we know it wouldn't work in a place like the huge Saturn moon Titan ...
More than 3 billion years ago, Mars was a very different place. It wasn't the rusty, dead seeming world we see today. Instead, lakes, rivers, and deltas likely covered much of the planet's surface.
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