Radiometric dating of ordovician period

The Cambrian is divided into four epochs (series) and ten ages (stages).Currently only two series and five stages are named and have a GSSP.The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is difficult as the occurrence of very similar trace fossils belonging to the Treptichnids group are found well below the T.

In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, mya; also known as Late Cambrian, Merioneth or Croixan).The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional.Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized—hence readily fossilized—organisms became common.However, average temperatures were 7 degrees Celsius higher than today.There were likely polar ice caps and a series of glaciations, as the planet was still recovering from an earlier Snowball Earth.

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