A Trip Through Geologic Time

The Geologic Time Scale 1. All of earth’s history is divided up-like parts of a play- acts, scenes, lines, etc. 2. We use eons, eras, periods, and epochs. 3. There are four eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic. 4. Precambrian is the longest, lasting 4 billion years. That’s 87% of all of earth’s history!

Precambrian Earth

The Beginning of Earth 1. The solar system began as a huge cloud of gas and dust 4.6 billion years ago. The cloud collapsed forming the sun and planets. 2. The denser elements sunk to the core- iron and nickel. The lighter elements made their way to the surface as lava from the interior. Scientists believe the crust was formed by 2.5 billion years ago. The oldest rocks on earth are called Precambrian shield and the one in North America is called the Canadian shield. Two early collisions of continents formed Laurentia and Rodinia.

Atmosphere 3. The first atmosphere was made of Hydrogen and Helium. Then there was a thick, poisonous atmosphere formed by volcanoes. 4. Then earth cooled off, water vapor condensed into the oceans. There are theories that water on Earth may have come from comet collisions. We had a warm and humid atmosphere with storms producing lightening. This is where life can begin.

The Precambrian Era- The beginning of life 1. The first life began somewhere between 3.9 billion years ago and 3.5 billion years ago. Life began in the oceans. Amino acids were the first organic molecules. The first life may have formed at hydrothermal vents in the deep sea. Single celled bacteria were the first life on earth. Then came seaweed, jellyfish, worms, sponges and corals.

Paleozoic Era- Life comes onto land 1.There is abundant life in the seas, the “Cambrian Explosion.” 2.Trilobites and brachiopods are abundant. 3.In the Ordovician period, there are many changes in sea level and tectonics continues to move continents and make mountains. First jawless fish are in the seas. 4.Silurian period- First plants began to grow on land and jawed fish evolve.

Paleozoic Events The Devonian period is known as the “Age of fishes.” First sharks and the first amphibians evolve. Amphibians are organisms that live some in water and some on land. They were the first animals to exist on land.

1.On land, swamps begin to form and the first insects appear.

2. Different landmasses exist until Pangaea forms 2.Different landmasses exist until Pangaea forms. Our own Appalachian mountains form. 3.In the Carboniferous period, the first reptiles evolve. They live only on land. They have tough skin with scales or plates and their eggs have thick shells. They are quickly becoming the dominant animals on earth. 4.By the end of the era, there were many different types of trees on land.

The Permian mass extinction caused the extinction of 95% of life on Earth. One theory is that sea level dropped, taking away the marine environments for the organisms to live.