The Cambrian was first defined by Adam Sedgwick in England (Cumbria)
and Wales; Cambria is the Roman name for Wales. Since then, Cambrian-age
rocks have been found on every continent; they occur throughout North
America, where the Burgess Shale, in British Columbia, Canada, is
an especially significant deposit of Middle Cambrian rocks that preserve
soft-bodied organisms. Lower Cambrian rocks in Yunnan, China, preserve
the famous soft-bodied Chengjiang biota. In Antarctica, Upper Cambrian
rocks in the Ellsworth Mountains preserve a highly varied shelly fauna.
Cambrian-aged shelly fossils occur widely throughout Australia, Europe,
the Lena and Aldan River areas of Siberia, and in North Africa.
Cambrian rocks were deposited between 543 and 490 million years ago,
and they are now defined as the first period of the
Era; it is at this time that animals having shells (exoskeletons)
become widespread in the fossil record. Before the Cambrian, in the
late Neoproterozoic Era (often called the Vendian), Earth had multicellular
life; however, the organisms were soft bodied. This Vendian soft-bodied
biota occurs in the famous Ediacaran beds of South
Australia and now has been found in many other parts of the world.
Before the Vendian, life was largely represented by single-celled
organisms such as Archaea, filamentous microorganisms,
algae, and other organisms that are studied by using microscopes.