Shales

... because relative to other geological eras, a lot of new forms did indeed appear. If you look at the fossils from one site, e.g. the Burgess shales, you do see forms appearing "suddenly" without evidence of intermediate forms in lower strata at the same site. This is probably because ...

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... simple indicator of seismic stress and deep ground movement. Radon is relatively high in uranium-rich rocks such as ancient granites, high-organic shales and coal beds. (Coal burning is a major source of uranium pollution.) The US map of potential radon reflects this geological factor. The Radon ...

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