Ammonites. London: The Natiral History Museum. 159 p by Monks N., Palmer P.

By Monks N., Palmer P.

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Extra resources for Ammonites. London: The Natiral History Museum. 159 p

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AMMONITE FOSSILS FOSSILS are the remains of organisms that have been preserved in sediments. Some fossils are found in unusual sediments, like the famous tar pits of La Brea in California, or the permafrost of Siberia, but most fossils come from marine limestones, clays and sandstones. Marine environments have high rates of sedimentation, burying corpses quickly, and increasing the chances of fossilisation. Over time, replacement of the original structure of the organism with minerals preserves its overall shape, producing a fossil.

Although squids do not have chambered shells, some have evolved an alternative method of acquiring neutral buoyancy - the use of lightweight chemicals in their tissues, typically ammonium ions (NH;). To understand why ammonites had such a diverse array of shell shapes, we must first understand how they worked in relation to buoyancy, water pressure, orientation, and streamlining. BUOYANCY In the third century BC, the king of Syracuse (modem-day Sicily), Hieron 11, commissioned a goldsmith to ~roducea new crown to be used in an upcoming religious festival.

Note that the weight of the object, or the substance it is made of, is irrelevant. Archimedes would displace the same amount of water whether he was made of flesh and bone, bronze or wood. It was this fact that revealed how Archimedes could solve King Hieron's problem, and supposedly he was so excited by his discovery that he ran straight to the palace, without stopping to put on his clothes, shouting "Eureka! Eureka! I've got it! " History does not record exactly how Archimedes employed his observations to test the quality of the crown.

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