The Ocean Floor—Its Secrets Revealed
IN ORDER to grasp the meaning of the things seen by researchers on the Alvin, we need a little insight into the way the earth is made. The ground beneath our feet is understood to be made up of a rigid layer (called the lithosphere) that rests on a mass of molten, slow-flowing rock. Apparently, this rigid outer layer averages some 60 miles [100 km] in depth and makes up only about 0.6 percent of the volume of the planet. The outermost part of it, the crust, is uneven, thicker beneath the continents and as thin as 3.5 miles [6 km] beneath the mid-ocean ridge system.
Furthermore, this solid outer shell is not one piece, like the shell of an undamaged egg. Instead, it appears to be broken into a number of large, rigid plates and many smaller ones, all of which are called tectonic plates. These make up the continents and ocean basins. The plates move in relation to one another. Where they draw apart, they thin out and form the rifts of the mid-ocean ridges. Worldwide, plates move at an average of about one inch [3 cm] per year.
According to the plate tectonic theory, as the plates diverge along the ridge system, they allow hot rock from the mantle, the region below the crust, to rise. The hot material forms new oceanic crust along the rift zone, but this does not result in the plates’ fusing together. Instead, they continue to part, which makes the rift system resemble a massive wound that never heals.
While a plate has new layers added to it at the mid-ocean ridges, its other extremity slowly slips beneath its neighbor and descends into the hot mantle below. There it becomes assimilated into the mantle. The region where a plate descends is called a subduction zone. Subduction zones contain some of the world’s deepest trenches. The Mariana Trench off Guam in the Pacific Ocean, for instance, is over 36,000 feet [11,000 m] deep. Were Mount Everest, the highest terrestrial mountain, placed in this trench, its summit would still be 7,000 feet [2,000 m] below sea level!
An Oasis—Of Toxins!
Because of its highly unstable and volcanic nature, the globe-encircling mid-ocean ridge system is riddled with lava flows and hydrothermal vents. The vents spew out a toxic, superheated concoction of water and dissolved minerals from inside the earth. Yet, amazingly, this inhospitable realm, which is also under pressures hundreds of times greater than those at sea level, does not repel life but, rather, attracts it—and in abundance! The hundreds of species living there include bacteria, giant clams—perhaps a foot in length—and, strangest of all, thickets of crimson-plumed tube worms anchored firmly to the seafloor and standing up to six feet [1.8 m] tall.
When brought to the surface, vent creatures smell like rotten eggs! The stench comes, not from decay, but from hydrogen sulfide—an offensive-smelling and highly poisonous chemical that is abundant in hydrothermal vents. Vent water is also highly acidic and contains many metals, including copper, magnesium, iron, and zinc. But instead of barely coping in this environment—which has been compared to a toxic-waste site—tube worms and other creatures thrive! How? In order to understand, let us take a closer look at the tube worm.
A Living Enigma
When biologists examined the tube worms, they found the animals to be a living enigma. They had no mouth and no digestive system. The question arose, How did they eat and assimilate food? Then came a startling discovery: The worms had red blood—not a bloodlike fluid but actual blood rich in hemoglobin—circulating through their body and featherlike plume.
The mysteries deepened when biologists opened up the flaccid sac of the tube worm’s body. Its tissues contained a bacterial culture composed of some 285 billion [10 billion] bacteria per ounce [gram] of tissue! In 1980 a biology student theorized that the tube worm lives by means of symbiosis—an arrangement where two species cooperate for mutual benefit. Research confirmed her hypothesis by showing that the tube worm, as host, feeds the bacteria, and the bacteria feed the worm.
Like gills, the plumes of the tube worm gather the ingredients, such as oxygen and carbon, that the bacteria need to manufacture food. The plumes do not wave directly in the searing vent water—that would be suicide—but in the region close to where near-freezing seawater and vent water mix. Of course, this food-manufacturing process requires energy. On the earth’s surface—and in the upper part of the ocean—sunlight energizes food production by causing vegetation to grow. But sunlight comes nowhere near the abyssal home of the tube worm.
Energy From the Belly of the Earth
Ingeniously, the Creator has arranged for the belly of the earth to provide the necessary energy via the hydrothermal vents and that obnoxious-smelling compound hydrogen sulfide. As the “sunlight” of the vent community, hydrogen sulfide provides the energy that the bacteria need to have to go about their food-manufacturing business. Meanwhile, the bacteria are the “plants” of the vent community because they are at the base of the vent food chain. *
In order to bind all the chemicals needed by the bacteria, tube worm blood is composed of hemoglobin molecules that are 30 times larger than hemoglobin molecules in humans. The blood transports these chemicals to the hungry bacteria, and the bacteria, in turn, manufacture food for the tube worm.
Vent Life—A Zoo of Organisms!
Indeed, no vent creature ought to go hungry, for bacteria blanket practically everything—at times up to inches thick! Even in the warm turbulence above the vents, bacteria sometimes congregate in great blizzards, forming, in effect, a living soup. Like tube worms, some animals enjoy a symbiotic relationship with the bacteria, while others graze directly on these microorganisms. Indeed, vent communities are so productive and energetic that they have been compared to salt marshes, tropical rain forests, and shallow-water coral reefs.
In fact, some 300 new species have already been identified near the vents. These include giant white clams and mussels (pigment is superfluous in a world of eternal night), octopuses, and voracious white crabs that relish the delicate plumes of tube worms. For protection, the worms have a snappy reflex that promptly retracts the plume into the safety of the tube.
Other vent creatures include sea spiders, snails, dancing shrimps, limpets, copepods, eellike fish that slither about on the bacteria- and sulfur-laden surfaces, smaller species of tube worms, and other worms. The latter include spaghetti worms and Pompeii worms. Appropriately named, spaghetti worms resemble handfuls of white spaghetti draped over rocks. What makes the Pompeii worm unique is its ability to tolerate temperatures of up to 176 degrees Fahrenheit [80°C.]! Of course, vent bacteria, which coat the Pompeii worm, are also able to withstand high temperatures. *
An Eerie Light!
In 1985, scientists were surprised when near the vents they found shrimps that have two eyelike organs with light-sensitive chemicals but no lenses. Of course, the first question that came to mind was, What could these animals possibly see in a world of total darkness? In order to find out, researchers made use of a highly sensitive digital camera, such as is used to photograph faint stars. They aimed the camera at a vent, turned off all their lights, and took a picture.
The result was amazing. The picture revealed “a dramatic, unequivocal glow with a sharply defined edge” where the jet of hot water left the chimney, says scientist Cindy Lee Van Dover. Do the shrimps exploit this eerie light, which is invisible to human eyes? Whatever the case, the discovery that hydrothermal vents glow “opens up a whole new area of research,” adds Van Dover.
The Biggest and the Smallest
Recently, a section of methane-rich seafloor was found to be home to the largest bacteria known to science. Discovered in 1997, these giants, which resemble a string of beads, are from 100 to 200 times longer than the average bacterium. They are also big eaters, leaving barely a trace of toxic sulfides in the sediment, thus making the area safe for other marine creatures.
What may be earth’s smallest living organism was also recently found under the sea, although in this case three miles [5 km] under the seabed! A report in The New York Times describes the discovery, made off Western Australia, as “so bizarre as to have touched off hot international debate.” The main point at issue is whether or not the entities—called nanobes because their size is measured in nanometers, or billionths of a meter—are living organisms. They resemble fungi, are roughly the same size as viruses, have DNA, and seem to reproduce quickly, forming dense colonies.
So much life is now being discovered that many scientists believe that the total mass of microbial life hidden inside the earth’s upper crust may exceed by far the mass of all the surface life! These discoveries are kindling a revolution in scientific thinking. One scientist said: “Dogma in microbiology is out the window in the past few years. The field has rediscovered itself. It’s essentially a new science.”
What is more, these truly profound discoveries teach us something that transcends science. The Bible captures the essence of this insight: “[God’s] invisible qualities are clearly seen from the world’s creation onward, because they are perceived by the things made.” (Romans 1:20) For instance, God is very concerned about cleanliness. This is evident in the bacteria and other sea creatures that help to detoxify many potential poisons coming from inside the earth and from decaying matter settling down from the ocean above. Clearly, God is concerned about the health of the planet and of all living things on it. As we will see in the following article, this personality trait of the Creator guarantees a glorious future for all terrestrial life.
^ par. 14 The chemical process employed by vent bacteria is called chemosynthesis. The term contrasts with photosynthesis, the light-energized process employed by land vegetation and by phytoplankton. The latter consists of plants or plantlike organisms that are found in the upper, light-bathed part of the ocean.
^ par. 19 In the 1960’s, scientists began to study heat-loving bacteria found in hot springs at Yellowstone National Park in the United States. Because of these amazing “borderland ecosystems,” says the book The Deep Hot Biosphere, “scientists first came to appreciate the extraordinary talents of the earth’s seemingly simplest forms of life.”
[Box/Picture on page 7]
What Are Hydrothermal Vents?
Along the volcanic mid-ocean ridge system, seawater creeps down through cracks in the crust to areas that are extremely hot. The water then becomes superheated, reacts with rock, and absorbs a number of chemicals. It also becomes more buoyant, rises to the seafloor, and forms hydrothermal vents—hydrothermal springs or geysers. These “easily rival their terrestrial analogs in power and spectacle,” says one reference.
Furthermore, the temperature of these seafloor springs can approach 750 degrees Fahrenheit [400°C.], which is hotter than molten lead! But because of the pressure exerted by miles of ocean above, the superheated brew does not turn to steam. Amazingly, less than an inch away from a hot jet, the ambient sea temperature is usually just a few degrees above freezing. Minerals precipitating out of quickly cooling springs settle to the seafloor, where they form mounds and chimneys. The latter may rise to 30 feet [9 m]. One chimney, in fact, was found to be 150 feet [45 m] high and nearly 40 feet [10 m] in diameter, and it was still growing!
Hydrothermal vents can turn on and off sporadically, which makes life around vents a precarious existence. Some creatures, however, may survive by migrating to other vents.
P. Rona/OAR/National Undersea Research Program
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Beginning in the 1970’s, scientists working off the North American coast discovered deposits of a remarkable substance called methane hydrate—a combination of frozen water and the flammable gas methane. The methane is given off by microbes in the mud. These microbes eat organic matter that has settled down from the ocean above. The methane then combines with near-freezing water to form crystals of methane hydrate. These crystals are like tiny cages of ice that trap methane inside. For the crystals to form, the water must be just above the freezing point and the seafloor must be under at least 1,600 feet [500 m] of water. When these conditions are met, crystals of methane hydrate grow, forming an effervescent, snowlike substance. When a lump of it is brought to the surface and ignited, it burns, giving off a reddish flame. Afterward, all that remains is a puddle of water.
Methane hydrate is a rich energy source. Scientists estimate that deposits of it total about twice the reserves of all other fossil fuels combined! (Fossil fuels include coal, oil, and natural gas—of which methane is also a prime component.) So far, though, this enormous resource has been out of reach because methane hydrate readily decomposes when removed from the environment in which it forms.
Methane hydrate beds also contain vents and chimneys, but the fluid gushing from these is cold, unlike the hot springs of the mid-ocean ridge system. However, because the vents release toxic plumes of methane, hydrogen sulfide, and ammonia, they nurture thriving communities of tube worms, clams, chemical-eating bacteria, and numerous other creatures. The chemical waste from these methane-eating bacteria leads to the formation of limestone—the same harmless substance coral is made of. *
^ par. 42 When bacteria oxidize methane, they form a compound called bicarbonate. This combines with calcium ions in the seawater to form calcium carbonate, commonly known as limestone. Limestone can be found all around cold vents as well as in vent chimneys.
[Diagram/Picture on page 4, 5]
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Mantle (partly molten)
When plates move apart, rifts form
The mid-ocean ridge system weaves around the earth like the seam on a tennis ball
NOAA/Department of Commerce
[Map on page 7]
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Major Ocean Rifts and Trenches
1. Mariana Trench
2. East Pacific Rise
3. Galápagos Rift
4. Mid-Atlantic Ridge
NOAA/Department of Commerce
[Picture on page 8]
Mussels are found at a depth of half a mile [1 km] in Green Canyon, Gulf of Mexico
J. Brooks/OAR/National Undersea Research Program
[Picture on page 8, 9]
Their delicate plumes contain blood rich in hemoglobin
OAR/National Undersea Research Program
[Picture on page 9]
These creatures commonly feast on tube worms
I. MacDonald/OAR/National Undersea Research Program
[Picture on page 9]
Perhaps a foot in length, these were found at a depth of 1.7 miles [3 km]
A. Malahoff/OAR/National Undersea Research Program
[Picture on page 9]
Some clams were brought to the surface
Photograph by William R. Normark, USGS
[Picture on page 9]
Some have two eyelike organs. But what can they see in total darkness?
EMORY KRISTOF/NGS Image Collection
[Picture on page 11]
Are they earth’s smallest form of life?
Dr. Philippa J. R. Uwins/University of Queensland