On what basis are the eras of the phanerozoic eon separated?
low birth rates
mass birthings
sparse extinctions
mass extinctions
The eras of the Phanerozoic Eon are separated by mass extinctions . During these events, large numbers of organisms became extinct very rapidly. There have been several extinctions in the Phanerozoic. Two mass extinctions stand out more than the others. One took place at the end of the Paleozoic. The other took place at the end of the Mesozoic.