Lecture 21-new

Lecture 21-new - Lecture 21: The Earths Early Climate and...

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Lecture 21: The Earth’s Early Climate and its Variability We are only beginning to appreciate the role of climate change in the profound evolution of biotic communities throughout Earth history.
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The Stage of Earth History 90% of Earth history occurred before the advent of complex life. This is the Pre- Cambrian Eon.
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Why did life originate in the World’s oceans rather than on land? Partly because climate conditions permitted dangerous levels of ultraviolet radiation to reach the Earth’s surface (no ozone layer)
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PreCambrian Earth and First Life Our first evidence of life on planet Earth comes from rocks ~3.2 billion years old. They were early forms of bacteria (one-celled) living in the world’s oceans. They were followed soon by photosynthetic microorganisms (one-celled), which started to form an oxygen-rich atmosphere. A real oxygen-rich atmosphere did not appear, however until ~500-700 million years ago. Climate as we know it did not start until enough oxygen was
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Lecture 21-new - Lecture 21: The Earths Early Climate and...

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