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Geoscientists probe Grand Canyon to determine how "explosive" the Cambrian Explosion really was

For being silent, sedimentary rocks have a lot to say. Take the Grand Canyon, for example. Carved by the Colorado River for at least five million years, the resulting cross-section reveals a chronological layer-cake record of Earth’s history. For Boise State geosciences professor Mark Schmitz and doctoral student Mike Mohr, the layers of the Cambrian time period are particularly rich.

The Cambrian Explosion is a popular term used to describe a biologic shift chronicled in the sedimentary layers at the beginning of the Cambrian period, around 540 million years ago. In the base of this rock layer are a profusion of preserved fossils with shells, skeletons and body-plans that did not exist prior, such as trilobites and brachiopods. At a glance, it would seem almost as if a single, sudden event in earth’s history sparked this shift. However Schmitz and Mohr’s research goes much deeper into the rock’s history to reveal another story.

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