1: Introduction

A BIT of GEOLOGY

Pre-Darwinian ideas William Smith ( ): discovered the succession of kinds of rocks and fosssils through time.

Pre-Darwinian ideas Charles Lyell ( ) and James Hutton ( ) "uniformitarianism" = present as key to the past;

“Modern” history of geology Alfred Wegener ( ): Theory of Continental Drift, 1912; theory not widely accepted for years. The theory of plate tectonics (meaning "plate structure") was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and other geologic phenomenon.

coincidence?

slow process

Cynognatus Mammal like reptile of the triassic

Glossopteris

Mesosaurus

Lytrosaurus

Small problem A scientific weakness in Wegener theory, however, was that he could not explain how continents could drift. Wegener suggested that the Earth’s rotation and tides moved the continents. Calculations, however, showed that these forces were too small to account for continental drift!!!!

Land bridge An alternative to Wegener theory

The Theory of Seafloor Spreading

Sonar discoveries One of the most important discoveries was a 70,000-kilometer (43,497-mile) mountain range that extends through the Atlantic, Indian, and Pacific Oceans.

Theory of seafloor spreading. Scientists began to notice patterns in the mid- ocean ridges, trenches, and rift valleys that proved pivotal in developing new theories. In 1960, geologists Harry Hess and Robert S. Dietz proposed an explanation of seafloor features. They hypothesized that the seafloor is in a constant state of creation and destruction through a process called seafloor spreading.

The Unifying Theory: Plate Tectonics In 1965, Canadian geophysicist John Tuzo Wilson introduced a new theory that united the theories of continental drift and seafloor spreading. This was the birth of today’s theory of plate tectonics. This theory combined ideas from both theories, along with some of the original isostatic equilibrium concepts.