Are planet earth was formed about 4.5 billion years ago. The there are 4 major eras of the Earth's history. They are the Precambrian Era, Paleozoic Era. Mesozoic Era, and Cenozoic Era. This book will include information on the eras and when they occurred.

Background

Info

Upper right: Precambrian era, Upper left: Paleozoic era, Lower left: Mesozoic era, Lower right- Cenozoic era

The Precambrian era went from 3.5 billion to 543 million years ago. It took 3/4 of the Earth's history. It had animals like jelly fish and sponges.

There are 3 time periods in the Precambrian era. They the Hadean, the Archean, and the Proterozoic. The Hedean time period was between 4.5-4 billion years ago.

A major event of the Precambrian era occurred in the Hadean time

Chapter 1

The Precambrian era

period that took the whole Hedean. What happened was that sand and dust was pulled to the earth. The sand and dust were heated by Friction, which is when 2 objects rub against each other. The heated dust and gas made the Earth full with lava. The water, and glaciers went bursting into the atmosphere, or gas that surrounds the Earth. Basically, during Hadean the whole solar system, or the sun with all the planets around it formed.

After that, another major event occurred during the Archean time period or eon. Which occurred from 4- 2.5 billion years. At that time blue and green algae. The Proterozoic time period was from 2.5 billion to 543 million years ago. It didn't have major events. The previous page shows the picture organisms (creatures) of the era.

Chapter 2

The Paleozoic era 

The Paleozoic era was between 543- 245 million years ago. Some creatures had back bones and some didn't. Some of the creatures were worms and Sea stars.

A major event that occurred in this era was the disappearing of large amounts of a species known as a mass extinction. During the mass extinction 90% of marine (water) life disappeared. Also, 70% of land species (creatures) got extinct. This happen in the end of the era or the

Permian time period.

By the way, the Paleozoic era had 6 time periods. They were Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Cambrian was from 541- 485 million years ago, and the Ordovician was from 485- 443 million years ago. Then, the Silurian was form 443- 419 million years ago, and the Devonian was from 419- 359 million years ago. After that, the Carboniferous was from 359- 299 million years ago, and the Permian was from 299- 245 million years ago.

Another major event was very long which took the whole era and ended before the mass extinction. It was the Cambrian explosion. The explosion increased oxygen levels, and because of it the Earth got more complicated creatures.

Chapter 3

The Mesozoic era

The Mesozoic era occurred from 245- 66 million years ago. It had more complicated animals such as dinosaurs, birds, and mammals. This era had 3 time periods. Triassic (245- 201 million years ago), Jurassic (201- 145 million years ago), and Cretaceous (145- 66 million years ago).

A major event of this era was an asteroid hitting the Earth. This happened at the really end of the era in the cretaceous time period. As, an effect all dinosaurs died or went extinct. This is known as the