A five-story crimson stain
In the Taylor Valley, one of the McMurdo Dry Valleys, a five-story-tall plume of red liquid pours slowly from the tongue of the Taylor Glacier. This feature, known as Blood Falls, was first documented in 1911 by Australian geologist Thomas Griffith Taylor, who initially hypothesized the color came from red algae. Decades of research have since revealed a far more complex origin rooted in geochemistry and ancient microbiology. The source is a subglacial pool of hypersaline water trapped under 400 meters (1,300 feet) of ice for at least 1.5 to 2 million years.
The water itself is clear until it reaches the surface. It is saturated with dissolved ferrous iron (Fe2+), scraped from the bedrock by the glacier's movement over millions of years. When this anoxic brine seeps through fissures in the glacier and makes contact with the atmosphere, the iron instantly oxidizes. This chemical reaction converts the soluble ferrous iron into poorly soluble hydrous ferric oxides (Fe3+), creating the red color. Recent analysis has identified these particles as iron-rich nanospheres, about 1/100th the size of a human red blood cell, which also contain silicon, calcium, and aluminum. The water's extreme saltiness—two to three times that of seawater—prevents it from freezing at the region's average temperatures.
An ecosystem without sunlight
The subglacial lake beneath Taylor Glacier is an isolated environment. Sealed off from the atmosphere, it contains a microbial ecosystem that has evolved in total darkness and without oxygen. Water samples from the falls contain at least 17 different types of microbes. These organisms are chemoautotrophs, meaning they derive energy from chemical reactions rather than photosynthesis.
This isolated ecosystem functions through a metabolic process never observed anywhere else in nature. The bacteria use sulfate (SO4^2−), a remnant of the ancient seawater, to "breathe." They metabolize trace amounts of organic matter trapped with them, using the abundant iron ions as part of the cycle. This discovery demonstrates that life can persist in cold and anoxic conditions, sustained entirely by geochemistry. For this reason, Blood Falls is an analogue for scientists looking for life in similar environments elsewhere in the solar system, such as beneath the polar ice caps of Mars or within the sub-surface oceans of Jupiter's moon Europa.