A brinicle, Sometimes huge ice stalactites form literally out of nowhere in the sea, stretching from the surface to the bottom. This phenomenon is called the "finger of death" because everything it touches freezes to death.

How brinicles form
A study found that when sea ice in the Arctic and Antarctic regions freezes, salt and other ions normally found in seawater get left out. Brine, which is concentrated salt water, gathers in various fractures and channels in the sea ice. Brine requires much lower temperatures to freeze and stays liquid until the ice cracks and the brine leaks into the ocean below. Being heavier than water, the ultra-cold brine sinks down to the ocean floor, freezing seawater it touches on its way down. This is responsible for the finger-like shape of the brinicles.

Notably, the downward-facing brinicle ice tubes, first discovered in the 1960s, form in a way similar to hydrothermal vents, which have been theorized as cradles of life on Earth. Hydrothermal vents form when ion-rich hot water gets ejected from the seafloor, creating a porous metal tower that extends upward. Water rushes through the tower, rupturing it, and causing more metal-rich water to expand the tower.

Could brinicles be cradles of life?
Study author Bruno Escribano of the Basque Center for Applied Mathematics in Spain explained that, like hydrothermal vents, brinicles also could have played a role in the origin of life. “Inside these compartments inside the ice, you have a high concentration of chemical compounds, and you also have lipids, fats, that coat the inside of the compartment,” he shared. “These can act as a primitive membrane — one of the conditions necessary for life.”