1

• The spectacular eruption of a volcano, the terror brought by an earthquake, the magnificent scenery of a mountain valley, and the destruction created by a landslide all are subjects for the geologist
• Physical geology


  Examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface
• Historical geology


  Aims to understand the origin of Earth and its development through time
• Different areas of geologic study

  • Archaeological Geology
  • Biogeosciences
  • Engineering Geology
  • Forensic Geology
  • Geochemistry
  • Geomorphology
  • Geophysics
  • History of Geology
  • Hydrogeology
  • Medical Geology
  • Mineralogy
  • Ocean Sciences
  • Paleoclimatology
  • Paleontology
  • Petrology
  • Planetary Geology
  • Sedimentary Geology
  • Seismology
  • Structural Geology
  • Tectonics
  • Volcanology
• Earth is a dynamic body with many interacting parts and a complex history
• Geology is perceived as a science that is done in the out of doors, and rightly so. A great deal of geology is based on measurements, observations, and experiments conducted in the field
• Geology is also done in the laboratory where, for example, the study of various Earth materials provides insights into many basic processes
• Geology frequently requires an understanding and application of knowledge and principles from physics, chemistry, and biology
• Geology is a science that seeks to expand our knowledge of the natural world and our place in it
• Natural hazards are a part of living on Earth. Every day they adversely affect millions of people worldwide and are responsible for staggering damages
• Geologic hazards are simply natural processes. They become hazards only when people try to live where these processes occur
• Geologic hazards

  • Volcanoes
  • Floods
  • Earthquakes
  • Landslides
• Resources represent another important focus of geology that is of great practical value to people
• Resources

  • Water
  • Soil
  • Metallic and nonmetallic minerals
  • Energy
• Geology deals not only with the formation and occurrence of these vital resources but also with maintaining supplies and the environmental impact of their extraction and use
• Geologic processes can be dramatically influenced by human activities
• Writings about fossils, gems, earthquakes, and volcanoes date back to the Greeks, more than 2300 years ago
• Aristotle's explanations about the natural world were not derived from keen observations and experiments, as is modern science
• In the mid-1600s James Ussher, Anglican Archbishop of Armagh, Primate of all Ireland, published a major work that determined Earth was only a few thousand years old, having been created in 4004 BC
• Catastrophism


  The doctrine that Earth's landscapes had been shaped primarily by great catastrophes
• Uniformitarianism


  The principle that the physical, chemical, and biological laws that operate today also operated in the geologic past
• James Hutton persuasively argued that forces that appear small could, over long spans of time, produce effects just as great as those resulting from sudden catastrophic events
• Today the basic tenets of uniformitarianism are just as viable as in Hutton's day
• We realize more strongly than ever that the present gives us insight into the past and that the physical, chemical, and biological laws that govern geological processes remain unchanged through time
• We also understand that the doctrine of uniformitarianism should not be taken too literally
• Estimates indicate that erosional processes are lowering the North American continent at a rate of about 3 cm per 1000 years. At this rate, it would take 100 million years to level a 3000-meter-(10,000-foot-) high peak
• Such events altered Earth's crust, modified its climate, and strongly influenced life on the planet
• Uniformitarianism


  The acceptance of a very long history for Earth. Although processes vary in their intensity, they still take a very long time to create or destroy major landscape features
• Erosion (processes that wear land away) gradually destroyed mountain peaks in portions of present-day Minnesota, Wisconsin, Michigan, and Manitoba
• The rock record contains evidence that shows Earth has experienced many cycles of mountain building and erosion
• Although many features of our physical landscape may seem to be unchanging in terms of the decades over which we observe them, they are nevertheless changing, but on time scales of hundreds, thousands, or even many millions of years
• James Hutton: '"The result, therefore, of our present enquiry is, that we find no vestige of a beginning, no prospect of an end."'
• Radioactivity was discovered in 1896 and has been used for dating since 1905
• The age of Earth is put at about 4.6 billion years
• Geologic time


  Vast time periods-millions or billions (thousands of millions) of years
• If you were to begin counting at the rate of one number per second and continued 24 hours a day, 7 days a week and never stopped, it would take about two lifetimes (150 years) to reach 4.6 billion
• Relative dating


  Events are placed in their proper sequence or order without knowing their age in years
• Law of superposition


  The youngest layer is on top, and the oldest layer is on the bottom
• Principle of fossil succession


  Fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be recognized by its fossil content
• Geologic time scale divisions

  • Eon
  • Era
  • Period
  • Epoch