Geologic+Eras

media type="file" key="Geologic Eras.mp3" width="240" height="20"

To make geologic time easier to understand, geologists have divided the earth's history into four time periods called eras. Each era represents a time of major sediment deposition and earth movement. While researchers do not all agree on their findings, the following account is widely accepted. An overview of these Eras is shown below. Complete the following exercise to help you discover what events occurred during which eras.

This video does a good job of summarizing the last 4.6 billion years. Watch it as you are finished your work and keep track of where you leave off each time.

Precambrian Era(earliest life)  Time Period (millions of years ago)  Began; 4600  Ended; 570  Major Geological Events; Precambrian shields, such as the Canadian Shield, Brazilian Shield, African Shield, and Australian Shield are formed  Major Biological Events; first multi-celled organisms  first single-celled organisms

 Paleozoic Era (ancient life)  Time Period (millions of years ago)  Began; 570  Ended; 245  Major Geological Events; periods when large parts of North America are covered by shallow seas  Appalachians formed  Major Biological Events; age of amphibians and fish first insects <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> large swamps-coal formed from this vegetation <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> first plants and animals appear on land

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Mesozoic Era (middle life) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Time Period (millions of years ago) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Began; 245 <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Ended; 66 <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Major Geological Events; formation of Rocky Mountains begins <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Innuitian Mountains formed <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> shallow seas in the interior of North America at various times <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Major Biological Events; age of reptiles, such as dinosaurs <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> first flowering plants <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> first birds and mammals

<span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;">Cenozoic Era (recent life) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Time Period (millions of years ago) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Began; 66 <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Ended; <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Major Geological Events; ice sheets cover much of North America <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> continents take on their present shape <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> formation of the Rocky Mountains completed <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> Major Biological Events; human beings develop <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> age of mammals <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 150%;"> modern forms of life evolve