The Marble Mountains, in California’s Mojave Desert, contain extensive exposures of Cambrian sedimentary rocks. The Cambrian is the oldest unit of the Paleozoic era, extending from about 540-490 million years ago, and is famous as the time when macroscopic fossils with “hard parts” first appeared. The most characteristic fossils of the Cambrian are trilobites, creatures distantly related to insects and crustaceans. Typically they consist of a mineralized head part (the “cephalon”), with segmented middle and tail parts. Because of its size and mechanical resistance, the cephalon tends to be the…
