Question

define palaeozoic era and coenozoic era in simple words

Answer 1

The Cenozoic Era began 65 million years ago with an asteroid impact that killed off a majority of the dinosaurs and ends at the present day
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. 

Answer 2

The Paleozoic Era started 542 million years ago with the emergence of complex life forms and ended 251 million years ago with the largest mass extinction the world has ever experienced. It is the oldest and longest era of the Phanerozoic Eon.