UNIFORMITARIANISM VERSUS CATASTROPHISM Page 234 in your textbook

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.

Hutton and the Principle of Uniformitarianism

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.

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.

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 1830 s. Armed with Hutton’s notes and new evidence of his own, Lyell successfully challenged the principle of catastrophism.

Modern Geology—A Happy Medium • During the late 20 th 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.

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.