The coldest period of the most recent ice age, just over twenty thousand years ago, was followed by several thousand years of erratic warming until, starting about twelve thousand years ago, global temperatures settled into the warmer and more stable regime that dominated human history during the Holocene epoch. By the end of the last ice age, our alien scientists would already have been very interested in the strange events afoot on planet Earth. As climates got warmer, the behavior of humans would become even more striking. Quite suddenly (on paleontological scales), humans gained access to
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