1. Which of the following is the correct order from oldest to most recent in the geological time scale? a) Mesozoic, Paleozoic Cenozoic b) Cenozoic, Mesozoic , Paleozoic c) Paleozoic, Mesozoic,Cenozoic d) Mesozoic, Cenozoic Paleozoic. What is the primary characteristic that defines the boundaries between different eons eras, and periods in the geological time scale? a) Climate changes (b) Mass extinctions and the appearance of new life forms c) Changes in Earth's magnetic field d) The shifting of tectonic plates a) The formation of Pangaea b) The extinction of the dinosaurs c) The appearance of the first mammals d) The first appearance of plants Which period is known for the first appearance of birds? a) Jurassic (b) Cambrian c) Silurian d) Devonian In which era did the first complex life forms, including plants and animals, appear? (a) Paleozoic Era b) Mesozoic Era c) Cenozoic Era d) Proterozoic Era