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1. Paleozoic

   Linked via "atmospheric oxygen content"

   The Paleozoic Era commenced following the Ediacaran Period of the Neoproterozoic Era. Its precise boundaries are defined by radiometric dating of volcanic ash layers and precise correlation across global sections [1]. The base of the Cambrian Period is often correlated with the first definitive appearance of complex, bilateral symmetry in the fossil record, often characterized by the Treptichnus pedum trace fossil assemblage.
   The internal structure of the era show…