1. Uniformitarianism Versus Catastrophism
Page 234in your textbook

2. The Principle of Uniformitarianism
Scientist James Hutton, the author of Theory of the Earth, proposed that geologic processes such as erosion and deposition has occurred on the Earth over time. This process takes a long time.
Uniformitarianism is the idea that the same geologic processes shaping the Earth today have been at work throughout Earth’s history.
The next slide shows how Hutton developed the idea of uniformitarianism.

3. Hutton and the Principle of Uniformitarianism

4. The Principle of Uniformitarianism, continued
Uniformitarianism Versus Catastrophism
Hutton’s theories sparked a scientific debate by suggesting the Earth was much older than a few thousand years, as previously thought.
A few thousand years was not enough time for the gradual geologic processes that Hutton described to have shaped the planet.

5. The Principle of Uniformitarianism cont.
To explain Earth’s history, most scientists supported the principle of catastrophism.
Catastrophism is the principle that geologic change occurs suddenly.
Supporters of this theory thought that mountains, canyons, seas, and other features formed during rare, sudden events called catastrophes.

6. The Principle of Uniformitarianism, continued
A Victory for Uniformitarianism Catastrophism was geology’s guiding principle until the work of geologist Charles Lyell caused people to reconsider uniformitarianism.
Lyell published Principles of Geology in the early 1830s. Armed with Hutton’s notes and new evidence of his own, Lyell successfully challenged the principle of catastrophism.

7. Modern Geology—A Happy Medium
During the late 20th century, scientists such as Stephen J. Gould challenged Lyell’s uniformitarianism. They believed that catastrophes occasionally play an important role in shaping Earth’s history.
Today, scientists realize that most geologic change is gradual and uniform, but catastrophes that cause geologic change have occurred during Earth’s long history.

8. Paleontology—The Study of Past Life
The history of the Earth would be incomplete without knowledge of the organisms that have inhabited our planet and the conditions under which they lived.
The science involved with the study of past life is called paleontology.
Paleontologist study fossils, which are the remains of organisms preserved by geologic processes.