The beginning of the phanerozoic is marked by what occurrence

The phanerozoic marks the period from around 541 million years ago to the present. This period began with the Cambrian Period, which is when diverse phyla of higher animals first appeared, including hard-shelled animals and animals with bone structures. This period also saw the first appearance of complex plants, fish, insects and tetrapods.

Because the earth is not round ,but it may seem round when viewed from ,our planet but true some points earth is not round was an oblate spheroid -a square that it squashed as globe however is not even a perfect oblate spheroid.in fact isaac newton's first proposed that earth was not perfectly round but it was an oblate spheroid instead.that mean a square that is squashed as its poles and swollen at the