Prehistoric Creatures Unit Study - Lesson 3: Pre-Cambrian Period

We studied the pre-Cambrian period of scientific history.

Surprisingly, it was a mass extinction event which gave rise to life on the planet during the Cambrian period of history. Before the Cambrian the only known life was single celled organisms. The seas were filled with a type of blue-green algae known as scienobacteria. Then a series of events took place which caused the Earth to freeze. It was the devastating ice age which caused the bacteria to evolve by surviving the harsh conditions.

Catastrophe: Miracle Planet is a series of videos which focuses on mass extinction events throughout the history of our planet. The first two episodes detail the ice age which took place between the pre-Cambrian and Cambrian periods of evolution.

Scientists believe the Earth was completely covered with ice at least two times since it was formed, hence the title of the video "Snowball Earth". At one time the air was filled with methane gas giving the atmosphere a reddish hue. Then one celled organisms which produced oxygen began to thrive changing the red to blue. The abundance of oxygen then caused the planet to freeze. Although the surface was frozen, forces beneath were still very active. Plates continued to move and volcanoes continued to erupt. Volcanoes erupting on the surface spilled carbon dioxide into the atmosphere. After years of eruptions, the carbon dioxide built up and rewarmed the planet. The increased temperature caused the ice to melt and life to once again thrive.

Episode 2 of Miracle Planet, Snowball Earth continued discussions of how the Earth was once completely covered by ice. 650 million years ago, there were no plants and animals to balance the carbon dioxide, oxygen and other gases within the atmosphere. Scienobacteria, one of the only living creatures, absorbed carbon dioxide. After years of carbon dioxide use, the gas became depleted in the atmosphere. Since carbon dioxide keeps the Earth warm, the lack of carbon dioxide allowed the planet to freeze. In addition to exploring how the Earth froze and later thawed, scientists explored winter caves to see how single celled organisms may have survived when the Earth was frozen and explained how they had altered DNA which enabled them to survive. It was this mass extinction event between the Pre-Cambrian and Cambrian period that was the turning point for life to thrive.

To gain a better understanding of how the Earth and Universe were formed, please refer to our earlier Earth Science study.

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