Complex, invertebrate, life forms are common as fossils beginning with marine strata of Cambrian age. How long ago did the Cambrian period begin?

The beginning of Cambrian period was about 541 million years ago and ends about 484.5 million years ago.

Explanation:

Cambrian period is a geographical period that appears in Paleozoic Era and lasts at Phanerozoic Eon to the beginning of Ordovician Period and the name was given as most of the sedimentary deposits were found at that period The majority of living organism includes unicellular or some multi cellular complex life forms.

Most live forms were aquatic and arthropods were the most dominant animals in the water that are known by studying the fossil records. The species adapt themselves to change with the environmental variations.

Animals like Protichnites and Climactichnites were found during this period.

The fossil records also suggested the presence of euthycarcinoides that are the extinct arthropod species.