Carbon dating live snail

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A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite.Compression fossils, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues.Fossils vary in size from one micrometer bacteria to dinosaurs and trees, many meters long and weighing many tons.

Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.For this reason, one term covers the two modes of preservation: adpression.Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, and the isolation of proteins and evidence for DNA fragments.The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystalization, adpression, carbonization, and bioimmuration.

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