What reason did approximately 542 million years ago was selected to be the end of Proterozoic eon and the beginning of the Paleozoic era?

Answer 1

The transition from the Proterozoic eon to the Paleozoic era, approximately 542 million years ago, is marked by the appearance of diverse and complex life forms during the Cambrian explosion. This period saw a rapid increase in the diversity of multicellular organisms, including the first representatives of many major animal groups. The significant geological and biological changes, including the development of hard-bodied organisms and the establishment of complex ecosystems, define this boundary and signify a major shift in Earth's biological history.