Size comparison of the Challenger deep with Mount Everest. The location is so deep that Mt Everest could be placed within it and still have 1.6 km (1 mile) of water above it.
The maximum surveyed depth of the Challenger Deep is 10,911 m (35,797 ft) or 6.78 miles (10.91 km). (National Geographic puts the depth at 10,920 metres (35,800 ft) below sea level.) The pressure at this depth is approximately 1,095 times that at the surface, or 110 MPa (approximately 8 tons per square inch).[1]The HMS Challenger expedition (December 1872 – May 1876) first sounded the depths now known as the Challenger Deep. This first sounding was made on 23 March 1875 at station 225. The reported depth was 4,475 fathoms 8,184 m (26,850 ft), based on two separate soundings.A 1912 book, The Depths of the Ocean by Sir John Murray, records the depth of the Challenger Deep as 31,614 ft (9,636 m). Sir John was one of the expedition scientists, a young man at the time.All of the original reports of the Challenger expedition can be viewed at the Challenger Library.In 1951, about 75 years after its original discovery, the entire Mariana Trench was surveyed by a second Royal Navy vessel, captained by George Stephen Ritchie (later Rear Admiral Ritchie); this vessel was also named HMS Challenger, after the original expedition ship. During this survey, the deepest part of the trench was recorded using echo sounding, a much more precise and vastly easier way to measure depth than the sounding equipment and drag lines used in the original expedition. HMS Challenger measured a depth of 5,960 fathoms 10,900 m (35,761 ft) at 11°19′N 142°15′E11.317°N 142.25°E.In 1984, a Japanese survey vessel using a narrow, multi-beam echo sounder took a measurement 10,924 m (35,840 ft).
LifeformsOn their 1960 descent, the crew of the Trieste noted that the floor consisted of diatomaceous ooze and reported observing "some type of flatfish, resembling a sole, about 1 foot long and 6 inches across" lying on the seabed. The report has since been questioned, with suggestions that it may have been a sea cucumber. The video camera on board the Kaiko probe spotted a sea cucumber, a scale worm and a shrimp at the bottom.An analysis of the sediment samples collected by Kaiko found large numbers of simple organisms at 10,900 m (36,000 ft).[9] While similar lifeforms have been known to exist in shallower ocean trenches (> 7,000 m) and on the abyssal plain, the lifeforms discovered in the Challenger Deep possibly represent taxa distinct from those in shallower ecosystems.
The overwhelming majority of the organisms collected were simple, soft-shelled foraminifera (432 species according to National Geographic[10]), with four of the others representing species of the complex, multi-chambered genera Leptohalysis and Reophax. Eighty-five percent of the specimens were organic, soft-shelled allogromiids, which is unusual compared to samples of sediment-dwelling organisms from other deep-sea environments, where the percentage of organic-walled foraminifera ranges from 5% to 20%. As small organisms with hard, calcated shells have trouble growing at extreme (10,000 m) depths due to the lack of calcium carbonate in the water, scientists theorize that the preponderance of soft-shelled organisms at the Challenger Deep may have resulted from the typical biosphere present when the Challenger Deep was shallower than it is now. Over the course of six to nine million years, as the Challenger Deep grew to its present depth, many of the species present in the sediment died out or were unable to adapt to the increasing water pressure and changing environment.[citation needed] The remaining species may have been the ancestors of the Challenger Deep's current denizens.
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