INTRODUCTION

The purpose of the introduction is to show the variety of topics covered in this course and treat in detail specific concepts which are common to many topics

Hopefully the introduction will stimulate your interest for this course

Introduction

A. Definition of geology and the scientific method

• Geology is the science that examines the Earth, its form and composition and the changes that it has undergone and is undergoing

B. Time and geology

• time is a very important factor in the formation of geologic features--geologic processes usually act so slow that changes may not be visible during a lifetime--the two photos below were taken from the same vantage point nearly 100 years apart.
• click here to see photos

1.Relative time

• geologic events can be observed as happening in a sequential order and not a certain number of years ago
• in a sequence of 3 events, one happened first, another second and the other last

2. Absolute time

• refers to the number of years ago the geologic event(s) happened (usually the event(s) happened millions or billions of years ago)
• "elephant rocks" in SE Missouri formed over a billion years ago while the limestone rocks in the Springfield area formed about 350 million years ago
• radioactivity in rocks allows us to determine how old a geologic event is-we will study this in detail later
• the application of relative and absolute time concepts to geologic events was important in developing the geologic time scale

3. Geologic time scale

• consists of time divisions called eons, eras, periods and epochs
• eons are the longest in time duration, and epochs, the shortest
• specific happenings are associated with each division
• a division ends or begins based primarily on the changes in life forms on earth and times involving nondeposition or long term erosion of rock materials--the most important change in life forms found in the rocks as fossils would warrant a change from one eon to another and a lesser, but still important change, would warrant a change of one era to another and so forth down to the change of one epoch to another
• the extinction of dinosaurs established the ending of the Mesozoic era and beginning of the Cenozoic era--that boundary in time took place about 66.4 million years ago according to the geologic time scale
• many extinctions of life forms throughout geologic time may be caused by meteor impact with Earth
• click here to see the geologic time scale-the numbers on the chart refer to millions of years ago
• click here to see another time scale

C. Uniformitarianism

• is an important postulate in geology which states: "the same process(es) operating in the present to cause a geologic feature operated in same way in the past to cause a similar feature"
• the laws of nature are unchanging and the present is a key to the past

D. Earth materials (minerals and rocks)

1. Minerals

• naturally occurring individual chemical substances
• many have important uses--some examples are:
  • minerals as gemstones---sapphires, rubies, emeralds, amethyst
  • minerals as important sources of chemical elements---barium, iron, lead
  • minerals as precious metals---gold, platinum, silver
• minerals comprise the composition of rock families
  

click here to see minerals

2. Rock families

• igneous rocks
  • formed from the cooling of molten material (magma) at or near Earths surface (extrusive) or deep below (intrusive)
  • geothermal energy is available to us as the result of igneous rock activity
• sedimentary rocks
  • formed primarily in large bodies of water by physical, biological or chemical processes at low temperatures
  • formed in layers and contain fossils which lend important information on history of life on Earth--the layering nature of sedimentary rocks is one of the most common characteristic of this family of rock
  • click here to see stratified (layered) sedimentary rocks
• metamorphic rocks
  • formed from any pre-existing rock which is subjected to high temperature and/or high pressure conditions for long time intervals

3. Rock cycle

• shows the inter-relationship between the 3 rock families---how a rock family forms and the conditions which help bring about the change of rocks in one family to another
• click here to see  the rock cycle

E. Volcanic activity

• gasses and/or molten rocks emitted at surface of Earth
• click here to see a volcanic eruption
• eruption can be passive (gentle) or explosive (violent)
• The "ring of fire" circumscribing the Pacific Ocean basin is the largest concentration of volcanic activity on Earth
• there are benefits generated from volcanic activity such as fertile soils

F. Earth's interior, continental drift, and rock plates

1.Internal structure of Earth

• comprised of a crust, mantle, outer and inner core
• click here to see  the structure of the Earth

• a. crust
  • comprised primarily of a layer of granite (continental crust) and basalt layer (ocean crust)

• b. mantle
  • comprised of 3 sections, top and bottom portions are solid and center section (asthenosphere) is hot and viscous--some may include the asthenosphere and upper solid mantle as the "upper mantle"

• c. core
  • comprised of a top or outer liquid layer and a solid lower or inner portion-- both sections are comprised primarily of iron (Fe) and nickel (Ni)

• d. lithosphere
  • entire rigid outer portion of Earth above asthenosphere including outer (top) mantle and all the crust
  • this section also includes any rock deposited on top of the upper crust much later in formation than the upper crust
  • isostacy is a floating balance between the lithosphere and asthenosphere---this principle can explain why there are certain mountainous or elevated areas as well as certain low areas on Earth.  Isostacy can be caused by some of the following:
            a.  depression of lithosphere by the weight of sedimentation or glaciers
                forming on top of lithosphere
            b.  higher heat concentration in the lithosphere causing that portion
                 of the lithosphere to rise because it is less dense than the
                 surrounding rock of the same composition (heat or heated materials
                 rise). The less dense rock rises and breaks into cracks called faults or
                 fractures.

click here to see the detailed upper structure of Earth

click here to see another Earth structure illustration

2. Continental drift

• a single super "proto-continent" split into sections and drifted apart beginning about 200 million years ago
• much data supports this idea including the map fit (jig saw puzzle) of continents
• click here to see the "map fit"

3. Rock plate concept (plate tectonics)

• born from the continental drift concept and explains the lithosphere as a series of plates each bounded to another or others
• plates can move towards boundaries (convergent), away from boundaries (divergent), or along boundaries (transformed)
• convergent boundaries form trenches where rocks plunge into the asthenosphere and divergent boundaries form ridges or rifts
  where new rocks are formed
• the driving force of plate movement are convection cells
• click here to see world plates and boundaries
• plate boundaries are related to important geologic phenomena as volcanoes and earthquakes

G. Geologic structures

• deep seated folded rocks on a large scale can harbor important deposits such as oil, gas and faulted rocks can contain precious metals
• long term non-deposition or erosion of rocks can form unconformities which can aid in dividing geologic time
• click here to see more about unconformities

H. Weathering and erosion

• weathering is the breaking down of a rock or mineral material
• weathering can be chemical or physical
• click here to see the chemical weathering of a stone monument--note the pitting
• stream water, wind and glacial ice are important transportation agents
• an important product of weathering and erosion is soil--weathering and erosion acting together can form some spectacular landforms as Bryce Canyon in Utah
• click here to see Bryce Canyon

I. Surface streams and groundwater

• these are 2 very important sources of municipal water
• there are pollution problems associated with these which we will consider later in the semester---pollution sources as landfills, factories, septic tanks, etc.
• also important erosional and depositional features associated with these will be treated in detail such as caves and stalactites
• click here to see cave deposits
• important features as sinkholes formed from the action of groundwater can cause structural failure of buildings and considerable surface collapse
• click here to see a large sinkhole

J. Glaciers

• some depositional features caused by glaciers are important in the cement and concrete industries
• during the "Great Ice Age" of North America glaciers cut the basin of the Great Lakes and was the source of much of the lake water
• click here to see the extent of global ice cover during "Great Ice Age"
• the glacial ice of Greenland and Antarctica comprises about 96% of all global ice and if all of the ice melted sea level would rise about 215 feet which means any coastal land presently below 215 feet elevation would be submerged

K. Earthquakes

• seismology is the study of earthquakes
• the New Madrid Fault area in southeast Missouri produced one of the largest earthquakes in history in the early 19th century--a possibility of large earthquakes happening in the future in this area is high
• tsunami is a sea wave produced by an earthquake--these features have produced major damage in the past
• click here for seismic information
  click here for tsunami information

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volcanic eruption click to return

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a large sinkhole click to return

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