Along the Juan de Fuca Ridge, more than a mile and a half below the surface of the Pacific Ocean, molten magma from the Earth's mantle wells up, pushing the Pacific plate apart from the Juan de Fuca plate at roughly the rate a human fingernail grows, thus creating cracks in the sea floor. Sea water barely above freezing point pours through the cracks and deep into the earth's interior. There it heats up to more than 400 degrees C and collects minerals such as pyrite, sphalerite and silica. When this super heated water erupts back out through the sea floor, it promptly cools, dumping the minerals as it does so. These deposits pile up into vast forests of chimneys known as "black smokers". The smokers are home to the strangest ecosytems known, in which organisms get by without sunlight, using as an alternative source of energy the sulphurous gases spewed from deep inside the earth.