Science likes to travel far in search of new phenomena, but nature keeps reminding us that, really, we’ve yet to discover many things much closer to us. That was a clear lesson for researchers who dug up the oldest ice on record—an ancient piece of Earth’s geological history from roughly 6 million years ago.

For a paper published on October 28 in Proceedings of the National Academy of Sciences , the Center for Oldest Ice Exploration, or COLDEX, describes the enigmatic composition of a 6-million-year-old ice core collected from the Allan Hills, a family of frigid hills in southeastern Antarctica. By carefully studying the composition of tiny air bubbles, permafrost, and other frozen deposits inside, the researchers derived an impressive reconstruction of Earth’s atmosphere from millions

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