Deep Sea Hydrothermal Vents

Throughout the oceans of the world there exist undersea mountain ranges, which have formed as a

result of volcanic activity. These are formally known as rift zones – where the movement of tectonic plates is tearing the earth’s crust apart. As the oceanic crust stretches, it thins and is cracked by giant fissures. Magma from deep down wells up through these cracks and fissures, rushing to fill in the gaps created by the rifting of the plates. When the magma reaches the surface of the oceanic crust, it sometimes oozes out as lava on the ocean floor, creating new oceanic crust as it cools. In many places, the magma simply wells up beneath the weakened and thin areas of crust and fills in the cracks and fissures without ever breaking the surface. Scientists had suspected that the long chains of undersea mountains were geologically active zones of the earth’s crust and had predicted the existence of hydrothermal vents before the first human ever laid eyes on one. The hydrothermal vents were a direct result of the volcanic activity happening under all that ocean water, as opposed to dry land.

A hydrothermal vent is a lot like an underwater geyser. Sea water seeps down into the cracks and fissures created by the spreading of the sea floor, sometimes as much as two or three miles into the earth’s crust. As the water comes into contact with the veins and channels of superheated, molten magma, the sea water is superheated. Then the hotter sea water rises to the surface back through the fissures, carrying with it minerals leached from the crustal rock below. The superheated seawater then spews out of the holes in the crust, rising quickly above the colder, denser waters of the deep ocean. As the hot seawater and the cold seawater meet, the minerals suspended in the hot water precipitate out (clump together and drop out) right at the vent opening. This causes an accumulation, or build up, of the minerals deposited by the mineral rich water into some fantastic and geologically unique formations that have come to be called chimneys. One giant smoker discovered in 1991 reached 15 stories high!

Scientists have gone down to explore and study these deep ocean hydrothermal vents and were completely surprised to find the areas immediately around the vents teeming with abundant life. The temperature of the water coming out of the vents has been measured at the source and it varies from just 68 degrees to as much as 600 degrees Fahrenheit. At sea level, water reaches the boiling point at 225 degrees Fahrenheit, but down in the deep ocean around hydrothermal vents where the water can reach well over the boiling point, the water coming out of the vents doesn’t boil! What prevents the scalding hot seawater from boiling (turning into vapor) is the extreme hydrostatic pressure of all the overlying water. What surprised scientists was that there was an entire ecosystem, a community of diverse life forms, absolutely thriving in conditions that were previously thought to be inhospitable to any kind of life.

 

Gigantism

A characteristic of many deep ocean creatures which baffles scientists is the incidence of gigantism - ocean creatures that exist in shallower waters take on gigantic proportions when they take up residence down in deep ocean water.   On the bottom of the ocean around deep-sea hydrothermal vents, there is a profusion of life that thrives on the hydrogen sulfide (H2S) gas released from the vents. Some of the most impressive of the creatures that live here are the giant tube-worms. In shallower waters these worms are common, growing to about the size of your hand. But down in the deep ocean these creatures thrive in this really hostile environment, growing to amazing lengths of up to eight feet long. These tube-worms grow in large clusters around the vents and live inside hard, shell-like protective tubes that attach to the rocks. They live in a symbiotic relationship with a type of bacteria that may hold clues as to how life on earth began billions of years ago. These worms lack mouths, anuses, intestines and stomachs. Scientists were at a loss to explain how these tube-worms were getting nutrients to survive and grow. It turns out their insides are lined with bacteria that oxidize the H2S, turning it into usable nutrients for the worms. The bacteria, in turn, benefit from the relationship because the worms deliver blood-containing hemoglobin, which helps the bacteria to break down the sulfides.

Giant tubeworms that live around hydrothermal vents on the sea floor. These creatures are about the size of your hand in shallower waters, but in the ocean's deep they have been found as big as eight feet long!

 

Up until the discovery of these incredible bacteria (able to withstand the hottest temperatures of any other living thing on earth), scientists didn't believe it was possible for anything to survive in the extreme environment around deep ocean vents (extreme pressure, high temperature, no sunlight). The discovery of the deep-sea thermal vents and the communities of life they support has completely changed the way we define life, perhaps going a long way to explain how life on earth first began.