When did the phanerozoic eon begin

541 million years ago

Explanation:

The Phanerozoic Eon is the most recent eon. It started 541 million years ago, and it still lasts, thus we are living in this eon as well. The Phanerozoic Eon has seen lot of changes, from explosion of the life, to big catastrophic events, big changes in climate, changes in the continents and oceans, and most recently the appearance of the most intelligent species, the humans. Through this period the Earth has been dominated by fish, sinapsids, dinosaurs, mammals, all having their fair share of dominance on the planet. The continents have been constantly on the move, creating supercontinents on multiple occasions, but then falling apart and creating numerous small ones. There has been multiple mass extinctions as well, some caused by intense volcanic activity, some by meteorite impacts.

not: both offer magnification to the atomic level.