Okay so, we all know how the Earth ends, right? In six billion years or so, the Sun swells up into a red giant, and the Earth gets melted. Pretty straightforward.

But it turns out that /life/ on Earth will end long before that. There are reasons to think that the biosphere will collapse about a billion years from now — long enough!  But still long before the planet itself gets melted.

Why? Basically two reasons.

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