A Revised Geological Time-Scale

  title={A Revised Geological Time-Scale},
  author={Alison Holmes},
The time-scale constructed in 1947 was based on certain assumptions that have recently been shown to be wrong. Appalachian pegmatites dated at 350 million years (m.y.) and thought to be Taconic (Ordovician) are now found to be Acadian (late Devonian), while others, dated at 255 m.y. and thought to be Acadian can now be referred to the Permian. Other recent evidence consistently leads to an extension of the 1947 scale that carries the beginning of the Cambrian back to about 600 m.y. ago. The… 

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