Department of Biological Sciences and Geology

CHAPTER 1: INTRODUCTION TO GEOLOGY, P 1-10 Scan, P 11-19 read, study plate tectonics.

GEOLOGY - the study of the earth

PHYSICAL GEOLOGY (Geology 220)- examines materials composing the earth; includes processes that operate beneath and on the surface.

HISTORICAL GEOLOGY (Geology 210)- the study of earth's origin and its development through time; strives to establish an orderly chronological arrangement of the multitude of physical and biological changes that have occurred in the past.

WHY STUDY GEOLOGY? Geology is an "environmental science:" it is essential for understanding earth processes, and important to understanding both natural and anthropogenic catastrophes.

GEOLOGIC TIME - current estimate is that the earth formed around 4.6 billion years ago; the oldest rocks found on the surface are about 3.8 billion (old rocks crop out on coast of Greenland, core of Wind River Mountains in Wyoming, Australia, Africa). The older date for the earth is derrived from dating the moon and meteorites.

GEOLOGIC TIME SCALE [p. 6] - Names provided by geologists who studied fossil-bearing rock sequences in many areas around the world.



Explains continental drift an important theory championed by Alfred Wegener early in the 20th Century.

The LITHOSPHERE consists of rigid PLATES floating on a dense, viscous ASTHENOSPHERE. The lithospheric plates are in motion. The energy to move the plates comes from: heat left over from the earth's formation and from radioactive decay.

PLATE TECTONICS works like a "boiling pot with a skin on top" - hot rock rises; cooler denser rock sinks. Within the mantle, hot areas are rising beneath ocean ridges, cooler rocks are sinking beneath plate convergent zones (such as around the edges of the Pacific Ocean). The sinking rocks on the ocean plates are full of water and trapped gas that cause some of the rock to melt as it sinks. This molten rock rises to the surface and erupts as volcanos, outlining the approximate the sinking plate boundaries. We call these boundaries SUBDUCTION ZONES. (This subduction process is happening in many places along the Pacific Plate and gives the Pacific Rim its name "The Ring of Fire.")

PLATES consist of rocks of differing densities:

  • 1 Oceanic crust - density = 3.5 g/cm3
  • 2 Continental crust - density = 2.7 g/cm3
  • and 3 the underlying upper mantle

    The plates vary greatly in thickness. Ocean lithosphere varies from 10 to 100 km in thickness and continental lithosphere from around 100 km up to 250 km in thickness.

  • The tectonic processes that affect the earth's surface are most active along the margins of PLATES. There are three types of plate boundaries:


    The ROCK CYCLE represents a flow chart showing natural processes and earth products.

    Rock Cycle

    Important concepts of the rock cycle include:

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