GEOLOGY

Detailed explanation-1: -They appeared abruptly in the early part of the Cambrian Period and came to dominate the Cambrian and early Ordovician seas. A prolonged decline then set in before they finally became extinct at the end of the Permian Period, about 250 million years ago.

Detailed explanation-2: -The Cambrian Period marks an important point in the history of life on Earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the “Cambrian Explosion, ” because of the relatively short time over which this diversity of forms appears.

Detailed explanation-3: -Dating the Cambrian The International Commission on Stratigraphy lists the Cambrian Period as beginning at 538.8 million years ago and ending at 485.4 million years ago. The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites.

Detailed explanation-4: -The Cambrian Period was followed by the Ordovician Period. The period gets its name from Cambria, the Roman name for Wales, where Adam Sedgwick, one of the pioneers of geology, studied rock strata.

Detailed explanation-5: -By the end of the Precambrian, conditions were set for the explosion of life that took place at the start of the Cambrian, the first period of the Phanerozoic Eon (541 million years ago to the present).