History of the Earth
By: Kara Lehner
1. The Formation of Earth
3. A Usable Atmosphere Earth's oxygen level wasn't usable because it was almost nonexistent but around 2.5 billion years ago, the level began to rise. It was thought to have risen because of the Cyanobacteria, a bacteria that lived in the ocean and harnessed the sunlight through photosynthesis. | 4. Ocean's Form 3.8 billion years ago oceans were formed on Earth. The water came from two sources, outgassing from within Earth and comet bombardment. Out gassing is where molten rock releases gas by volcanic activity. Comets and meteoroids brought gases with them when they struck the Earth. The gases stayed in gas form until the Earth cooled to below 100 degrees Celsius where they then became rain and slowly collected on Earth creating the oceans. | 5. Vertebrates appear During the Cambrian Period, vertebrates came to life about 530 million years ago. The first vertebrate was a jawless fish called the agnathan. The agnathan was very common until it became extinct and was replaced by a jawed fish. |
3. A Usable Atmosphere
4. Ocean's Form
6. Plants Begin to Grow on Land
7. Largest Mass Extinction Ever!
8. The Age of the Dinosaurs
9. The Beginning of Ice Ages
10. The First Modern Humans
Works Cited
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Prehistoric Time Line, Geologic Time Scale, Photos, Facts, Maps, and More -- National Geographic. (n.d.). Retrieved from http://science.nationalgeographic.com/science/prehistoric-world/prehistoric-time-line/