Earth’s Atmospheric Evolution
Storyboard Text
- The Earliest Atmosphere
- Did you know that early Earth had 10-200 times more CO2 than today’s atmosphere!
- The Archean Eon
- 2.7 billion years ago, microscopic organisms called cyanobacteria flourished in Earth’s oceans. As cyanobacteria created more free oxygen, the amount of oxygen in the atmosphere increased.
- Oxygen at Last
- The grass is green and the sky is blue!
- (4.6 billion years ago) - This is the earliest stage of planet Earth. Earth has formed 4.6 billion years ago from a hot mix of gas and solids, the surface was molten and has almost no atmosphere. As the planet cooled, an atmosphere formed mainly from gases spewed from volcanoes (hydrogen sulfide, methane, and carbon dioxide). After about half a billion years, Earth's surface cooled and solidified enough for water to collect on it.
- The Oxygen Boom!
- In the late Proterozoic, oxygen levels in the oceans and atmosphere increased dramatically.
- (4 to 2.5 billion years ago) - At the time, there was zero oxygen on Earth, it was only found in compounds such as water. "Complex chemical reactions in the young oceans transformed carbon-containing molecules into simple, living cells that did not need oxygen to live," instead they made energy from sulfur and other elements.
- The Age of Oxygen
- (2.6 billion to 400 million years ago) - At last, life and Earth's atmosphere evolved. Over time, tiny photosynthetic organisms produced enough oxygen to react with methane in the atmosphere, transforming it forever. Around two billion years ago, the methane haze cleared and the sky became blue.
- Modern Atmosphere
- The Eocene Epoch was the warmest part of the past 65 million years. During the early Eocene, palm trees grew as far north as Canada, and forests of dawn redwoods covered Ellesmere Island near the North Pole.
- (700 to 550 million years ago) - Until about 430 million years ago, most aerobic organisms lived in the ocean and used oxygen dissolved in seawater. Then life on land appeared, small plants and invertebrates evolved the ability to live on land and use oxygen directly from the atmosphere. During the Devonian Period (416-397 million years ago), plants evolved, and so did the first four-footed animals.
- (400 million to 290 million years ago) - As plants became firmly established on land, life once again had a major effect on Earth's atmosphere during the Carboniferous Period.
- Early in the Carboniferous Period, Earth’s climate was warm. Later, glaciers formed at the poles, while equatorial regions were often warm and humid. Earth’s climate became similar to today’s, shifting between glacial and interglacial periods.
- (290 million years ago to now) - During most of the past 290 million years, Earth was much much warmer than it is today. Between 200 and 45 million years ago, polar ice caps were very small or absent, and winters were warmer around the globe allowing many types of plants and animals to live in polar regions.
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