In 2018 a team of British scientists was drilling through an Antarctic ice shelf, boring a borehole through nearly nine hundred metres of solid ice to sample the seawater and mud far beneath. They lowered a camera down the hole, expecting the lifeless dark of the sea floor. Instead the camera struck a boulder — and clinging to that boulder, hundreds of kilometres from the open ocean and sunlight, were animals. Stationary sponges and other unidentified creatures were living on a lonely rock beneath a roof of ice thicker than most mountains are tall. Nobody had expected anything there at all.
The most hostile address on Earth
To grasp why this was a shock, consider where these animals were living. An ice shelf is a vast floating slab of ice, an extension of the land-based ice sheet where it flows out over the sea. Beneath it lies a sealed cavity of seawater, permanently roofed by ice, permanently dark. The spot where the sponges were found lay under about nine hundred metres of ice and, critically, was estimated to be hundreds of kilometres from the nearest open water where sunlight could reach the sea and drive photosynthesis.
That distance is the puzzle. Almost all life on Earth ultimately runs on sunlight: plants and plankton capture it, and everything else eats them or eats the things that eat them. Stationary filter-feeders like sponges survive by straining food particles from the water that drifts past. But in a sunless cavity hundreds of kilometres from the open sea, where does the food come from? The current beneath the ice would have to carry nutrients an enormous distance in the cold and dark to sustain a community clinging to a rock. That such creatures manage it at all stretched scientists' assumptions about where life can hang on.
The hidden ocean beneath the ice
The sponges on their boulder are part of a larger revelation of recent decades: Antarctica's ice conceals whole hidden environments harbouring life. Buried far beneath the thick ice sheet of the continent's interior lie hundreds of subglacial lakes — bodies of liquid water kept from freezing by the pressure of the ice above and the faint heat of the Earth below, sealed off from the atmosphere for enormous spans of time.
The largest and most famous is Lake Vostok, which lies under roughly four kilometres of ice near Russia's Vostok research station — one of the coldest places ever recorded on the planet, where the air temperature has plunged below minus eighty-nine degrees Celsius. Lake Vostok is a body of water comparable in size to one of North America's Great Lakes, hidden entirely beneath the ice, and cut off from the outside world for what may be millions of years. Reaching it without contaminating such a pristine, sealed environment posed a formidable challenge, and drilling into these lakes has been controversial for exactly that reason. Studies of ice and water from Vostok and other subglacial lakes have turned up signs of microbial life adapted to the cold, dark, high-pressure, nutrient-starved conditions — microbes making a living in one of the most isolated habitats imaginable.
These discoveries carry an implication that reaches well beyond Antarctica. Several moons in the outer solar system — Jupiter's Europa and Saturn's Enceladus foremost among them — are thought to hide oceans of liquid water beneath thick shells of ice, warmed from within rather than from a distant sun. If life can persist in the dark, sealed, sunless water beneath Antarctica's ice, hundreds of kilometres from any light, then the frozen moons look a great deal more promising as places to search for it. Antarctica has become, in effect, a testing ground and a rehearsal for hunting life on other worlds.
The deepest lesson of the sponges on the boulder is an old one that keeps needing to be relearned. Wherever we go on this planet — the boiling vents of the deep sea, the driest deserts, the sealed lakes beneath four kilometres of ice, the black cavity under a floating ice shelf — we tend to assume nothing could possibly live there, and we tend to be wrong. Life is more stubborn, more inventive and more widespread than our intuitions allow. Drill through nine hundred metres of ice into water that has never seen the sun, and something, improbably, is already living down there.
Quiz nuggets
- In 2018 British scientists drilling through an Antarctic ice shelf found sponges living on a boulder under about 900 metres of ice.
- The site was estimated to be hundreds of kilometres from open water and sunlight, making the animals' food source a genuine puzzle.
- Hundreds of subglacial lakes lie buried beneath the Antarctic ice sheet, kept liquid by pressure and the Earth's internal heat.
- Lake Vostok, under roughly 4 km of ice near Russia's Vostok station, is the largest; the area holds a record low air temperature of about minus 89°C.
- These findings inform the search for life on ice-covered moons such as Jupiter's Europa and Saturn's Enceladus.