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Chapter 11: Earth History

Difficulty Level: At Grade Created by: CK-12
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How do you apply what you've learned so far to understanding Earth history?

Something that we hope you have learned from these lessons and from your own life experience is that the laws of nature never change. They are the same today as they were billions of years ago. Water freezes at 0o C at 1 atmosphere pressure; this is always true.

Knowing that natural laws never change helps scientists understand Earth’s past because it allows them to interpret clues about how things happened long ago. Geologists always use present-day processes to interpret the past. If you find a fossil of a fish in a dry terrestrial environment did the fish flop around on land? Did the rock form in water and then move? Since fish do not flop around on land today, the explanation that adheres to the philosophy that natural laws do not change is that the rock moved.

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Chapter Summary


Fossils are remnants of living creatures that can indicate something about the ecosystem and the environmental conditions that were present at the time they lived. Fossils can help geologists decipher the geological history of an area, as can clues from rocks. The principles of relative dating allow geologists to decipher the order of geological events and correlation allows them to determine the geological history of a region. Absolute age dating gives accurate dates for geological events, provided the proper materials are available and the proper techniques are followed. The most accurate and widely used absolute age dating technique is radiometric dating, which uses the ratios of radioactive isotopes to indicate age. Using these techniques, and some from astronomy, scientists have reconstructed a history of Earth and the solar system. The solar system began as a cloud of dust and gas that contracted by gravity until the center ignited to form a star and clumps of matter came together to form the planets. Shortly after Earth formed, a giant asteroid struck the planet, which melted both bodies, and flung material out into Earth's orbit. That material coalesced into the Moon. Earth had to cool before it could support an atmosphere, but when it did precipitation provided the water that filled the ocean basins. Life evolved slowly, and it was not until the evolution of photosynthesis that oxygen could collect in the atmosphere. The presence of oxygen led to the formation of the protective ozone layer and gases for animals to breathe. The early Earth was hot and so convection and plate tectonics were faster than today. From the time of the Archean, plate tectonics processes were similar to today. From then until now, supercontinents formed and broke apart, seas transgressed and regressed, and ice ages came and went.

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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Jan 14, 2016
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