| Fossils preserved in rock strata provide scientists with clues to evolutionary history. This stratigraphic column is based on paleontological evidence, and shows the order in which organisms appeared in the fossil-rich Paleozoic Era. Each layer represents a particular time frame and shows a representative organism which flourished during that time. Although fossils are rarely found in the idealized and localized fashion shown here, they are often in more or less chronological order. Generally, the oldest fossils appear in lower layers, and the most recent fossils at the top, so that placement may be used as an aid in dating the specimens. |
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