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Life at the Bottom of the Sea

Directions: Please read the following passage and answer all of the accompanying questions.


1 Under the Earth’s crust are a number of giant plates that shift and collide in dynamic processes that cause earthquakes and volcanic eruptions. Some of these plates are located in the middle of the ocean, where magma is erupting to form a new crust. These sites are called geothermal vents or smokers, and surprisingly they are teaming with life. Despite the harsh environment which can reach temperatures of up to 1000ºF, there are several species of crab, fish and bacteria that thrive in this area. In fact some scientists believe that life itself may have begun at one of these geothermal vents.


2 When plates under the Earth’s surface begin to shift, they often leave large fissures on the ocean floor. When the cracks appear, water is sucked down towards the center of the Earth, where it comes into contact with magma and then returns to the ocean floor super heated. These vents are deep on the ocean floor in areas where no sunlight can penetrate.
3 Scientists used to believe that sunlight was the source of all life. Photic energy was captured by plants and worked its way up the food chain as animals ate plants and then each other. Scientists were baffled at first by the abundance of life on the sea floor: giant tube worms (Riftia pachyptila), Brachyuran, Galatheid crabs, and various other fish. It was inconceivable that all of the energy necessary could drift down from the regions so far above where there was sunlight. In addition the giant tubeworm, Riftia, had no mouth or digestive system. With no way to digest food it seemed impossible that they could survive.


4 However, these animals were harboring bacteria in their bodies. Bacteria have been known to use chemical energy as the basis of their metabolism—they can use inorganic chemicals to produce energy. On the ocean floor there is a high content of hydrogen sulfide, a chemical that sulfide oxidizing bacteria use to run metabolic pathways. This process is very similar to what plants do with light but is named chemosynthesis instead of photosynthesis.
5 This was quite a break through since it was the first complex ecosystem ever discovered to exist completely independent of sunlight at every level of the food chain.


6 There are a couple more outstanding things about life at deep sea vents. One of these are the thermophilic, or heat-loving, bacteria that can survive at temperatures of up to 482ºF. Previously, life in microorganisms was only believed to be sustainable between the boiling and freezing points of water (32ºF to 212ºF). These have huge research and commercial applications. Since these high-temperature loving bacteria have enzymes that are stable at high temperatures they can be used in high chemical processing techniques. For example, Thermus aquaticus has a natural enzyme which is used in the polymerase chain reaction, an important process scientists use to make copies of fragments of DNA.
7 Furthermore, there is evidence that life itself may have begun on the sea floor. Nitrogen is one of the most important molecules for life and is present in the amino acids that make up every protein in our body. However, most nitrogen exists as N2, a practically inert chemical. Most scientists agree that for life to occur nitrogen has to be converted into a more reactive chemical like ammonia, NH3. When N2 is exposed to the chemicals present in the ocean, under the pressures and heats near volcanic vents, the result is ammonia which could then be used by newly developing life forms to create the proteins necessary for life.
8 It seems deep sea vents are a haven for life in a very hostile environment. Organisms can survive here without any exposure to light—a feat unparalleled on any other part of the planet. Some bacteria here can even survive at temperature beyond what any normal organism can withstand. Life itself may have even originated from the strange chemical cocktails at the bottom of the ocean. Deep sea vents truly hold many of the secrets of life.

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