The Mariana trench is the deepest point on Earth that is above the Earth’s crust.Located near Asia, the trench runs for nearly a thousand miles. First surveyed in 1951,the trench is thought to contain life not found any other place on earth and could behome to many undiscovered species and perhaps even several species thought to beextinct. Very inhospitable to the vast majority of ocean life, the Mariana Trenchremains vastly unexplored and has only been surveyed through the use ofunmanned probes. Once thought to be a barren area of the ocean with nothingmore than oceanic bacteria, the trench seemed to be the perfect submarine channel.Therefore, following the lead of England and the Soviets, the US Navy bathyscapheTrieste was lowered to the bottom of the trench in 1960, where two navy personnelonboard were astounded to see sole, flounder, and shrimp. In 1984 the Japanesesent a highly advanced research vessel to the trench and were able to record depthsof near 11,000 meters. However, the official depth was changed in 1995 after aJapanese probe was able to identify areas that were 13740 feet under sea level.
         The Mariana Trench, one of twenty two found trenches in the world's oceans, isnot only the deepest but also the widest. Formed by subduction of the ocean’s crusts,a trench is created when plates topped by oceanic crust are subducted betweenneighboring tectonic plates. Even at a depth of 36,000 feet, the bottom of theMariana Trench is home to thousands of species of sea life and is home to a complexecosystem. The ocean floor represents 80% of the Earth's biosphere, making eventhe Mariana Trench a place teeming with life. The Mariana Trench ecosystem issupplied by the large number of heat vents at the sea bottom. Spewing out sulfide,they supply food for barophilic bacteria which are then consumed bymicroorganisms. These microorganisms are consumed by crab and shrimp which arethen eaten by larger predators.
        The leftvent, an example of the seemingly bizarre sealife that can only be foundat deep depths, has watery flesh and poorly ossified bones. Some scientists attributethe poor ossification to one of the consequences for living at such great depths. Thepressure, constantly pushing on the bones of the leftvent, affects the ossificationprocess as it disrupts the smooth transfer of cartilage to bone. The leftvent is alsoone of several species with extreme sexual dimorphism commonly present in deepsea species. Females grow to 23 centimeters long while males only grow to 5centimeters. It is thought that the sparse population of larger fish like the leftventforces males to become parasites in order to ensure that a mate is accessible when itcomes time to breed.
        The enormous difference in pressure between the Mariana Trench floor andthat on the surface keeps deep sea species from mixing with species from shallowwaters. These conditions are so extreme that even a hungry shark is unable to swimdeep enough to prey upon trench sea life. A shark swimming along the bottom of thetrench would be crushed in less than a second. Humans are also unable to descendto the bottom without the help of technology. Surveys of the bottom of the MarianaTrench must be made with submersibles.
【題組】29. What can be inferred from paragraph 1?
(A) The Mariana Trench was once used for US submarine warfare.
(B) The U.S. was the first country to send a ship and record the depth of theMariana Trench.
(C) The depth of the Mariana Trench is volatile.
(D) It never occurred to the navy personnel that such complex life forms existed atthat depth.