Period of geologic time comprising the Palaeozoic, Mesozoic, and Cenozoic eras, it began approximately 542 Ma ago at the start of the Cambrian period and continues to the present day. It is marked by the accumulation of sediments containing the remains of animals with mineralized skeletons. Although the name is derived from the Greek phaneros meaning ‘visible’ and zoion meaning ‘animal’, the term is no longer used in the sense of ‘visible life’, but its commencement merely defines the base of the Cambrian.

http://www.geologypage.com/2013/12/phanerozoic.html Phanerozoic.