List the four eras on the geologic time scale describe one identifying type of organism from each era

The four main time scales, starting from the earliest, are:

Precambrian - This era consisted of single-celled organisms and multicellular organisms also began to arise in this time period.

Paleozoic - The early part of this era primarily had fish and the latter part of the era consisted of amphibians and reptiles.

Mesozoic - The mesozoic era had dinosaurs, birds and some flowering plants

Cenozoic - Many dinosaur species had gone extinct and this era contains mammals.