Chapter 15:5 Geologic Time Scale

Geologic Time Scale Divides Earth’s 4.6 billion year history into parts Our division of time: Day  Hour  Minute  Second Division in Geologic Time Scale: Eon  Era  Period  Epoch

Extinction Means death of every member of a species Most paleontologists agree on five mass extinction events in Earth’s history, but they do not agree on the cause of those events

Precambrian Era Lasted from 4.6 billion years ago to 543 million years ago First signs of life are bacteria in the water By end of this era, animals such as jellyfish and worms have appeared

Paleozoic Era Lasted from 543 million years ago to 248 million years ago First era we find fossils from By the middle of the era, we started to see plants on land By the end of the era, amphibians and reptiles lived on land and there were many insects Ended with largest mass extinction in Earth’s history (killed about 90% of species)

Mesozoic Era Lasted from 248 million years ago to 65 million years ago Known as the Age of the Reptiles because they dominated Divided into Triassic, Jurassic, and Cretaceous Periods

Mesozoic Era continued Triassic Period – Mammals appear and the first dinosaurs are appearing Jurassic Period – The Age of the Dinosaur begins and birds begin to appear towards the end Cretaceous Period – Dinosaurs dominate, T-Rex and Triceratops roam the Earth, but all dinosaurs will have died out by the end.

Cenozoic Era Lasted from 65 million years ago to the present Known as the Age of Mammals Divided into Tertiary and Quaternary Periods

Cenozoic Era continued Tertiary Period- Mild climate, it is believed that humanlike creatures began walking upright toward the end of this period Quaternary Period- climate turns very cold, last ice age ends about 11,000 years ago, and modern civilization begins