Antarctica has a waterfall that bleeds because it's been sealed for a million years

In 1911, geologist Thomas Griffith Taylor found a startling stain at the edge of a glacier in Antarctica's McMurdo Dry Valleys: a plume of water the color of rust, oozing from cracks in the ice onto a frozen lake below. Early explorers guessed red algae. The real explanation took nearly a century longer to nail down.

The water comes from a pool of ancient seawater trapped beneath roughly 400 meters of ice — a relic pocket of ocean sealed off by the advancing Taylor Glacier an estimated 1 to 2 million years ago, when sea levels were higher and this part of Antarctica was still connected to open water. The color comes from iron: the brine is rich in dissolved iron that turns red the instant it hits air and oxidizes, the same chemistry that rusts a nail.

What makes the site remarkable isn't the color. Geomicrobiologist Jill Mikucki and colleagues found at least 17 distinct types of microbes living in that sealed brine, in total darkness, with almost no oxygen, subsisting on a metabolism that runs on sulfate and iron instead of the sunlight or oxygen every visible ecosystem depends on. It's a chemical pathway barely observed anywhere else in nature.

The pool has had no contact with the surface world since before there were humans to name it. Scientists studying it now treat it as a working model for how life might survive on ice-covered moons elsewhere in the solar system — proof that a full stop from sunlight isn't automatically a full stop for life.