geology chapter 1 summary and overview
TRANSCRIPT
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Geology as a Science
Geology at first was an observational science
People would see a geologic curiosity and describe it Later, people would attempt to explain it
Modern geology combines observation and laboratory activities(measurements and calculations) to explain natural phenomena
Geology has grown rapidly into an analytical science Experiments must consider changes in temperature, pressure, stress, chemical
parameters, and time
Not just a descriptive science, but a more quantitative and moreinterdisciplinary science through time
Starting materials that form rocks and minerals often are completely changedduring the course of time
Geology is an environmental science Rocks record how earth has changed over time
Recognition and mitigation of natural hazards
Scientific MethodA means to discover basic scientific principles
Starting Pointa set of observations and/or a body of data from measurements ofphenomena and/or experiments
Hypothesisis formed to explain the observations or data
Conceptual framework or model is developed
Multiple explanations or equations developed
Must be testable and test must be reproducible
Proof of a hypothesis is sought as well as evidence to disprove it
Test the hypothesis repeatedly and systematically
Make set of predictions and perform series of experiments
Theoryformed as accepted explanation for an observation or set of data
Hypothesis becomes a theory only after extensive testing of the hypothesis
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Theory versus Hypothesis
Theoryaccepted explanation
Must be a well tested model
Is subject of considerable investigation and data collection that is required to
evaluate it
A hypothesis is elevated to a theory only after extensive debate and
experimentation
Geology and the Scientific MethodGeology has problems that other sciences do not!
Problems with size
A volcano is huge!
A river is not easily contained within a laboratory
Plate Tectonics involves the whole Earth
Problems with time
Geologic processes take millions of years to complete
Geologists are limited by human time (years to decades)
Problems with resolution of data
New technology and procedures often impact, or challenge, old theories
We can see more details now than a century ago
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Why Environmental Geology? Environmental geology explores the many and varied interactions between
humans and geologic environments
Earth is a dangerous place!
Earthquakes and Volcanoes
Floods, Mass wasting, and Soil erosion
Global Warming
Quest for more energy
Pollution and Storage of toxic waste
Find and manage fresh water
Find new resources (they are limited)
Remediate sites of mineral extraction
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Population Growth
Population has experienced exponential growth:
Possibly 9 billion people by 2050
Slow population growth up until mid-19thcentury Life expectancy has increased
Birth rates have greatly exceeded mortality rates
People are more mobile and can live anywhere
New perils will confront us because of our increasing population
Limited exploitation of new sources of natural resources
Growing demand by third world countries wanting to become first worldcountries
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Impacts of the Human Population
Rapid growth of humans results in problems obtaining an adequate food supply
Expected problems:
Water supply for irrigation, drinking, and industry
Farmland to produce crops to feed a hungry earth
Food production is an energy-intensive business
Supply of energy and minerals for our material based lifestyle
Pollution of air, land, and water pursuing
Population distribution by region in 2002 with
projection to the year 2050
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Global population density; the darker the shading, thehigher the population density.
Impacts of the Human PopulationHow do we resolve the issues?What are the consequences because of the growth of the human population?
Energy and natural resources are finite supplies on earth
Where do we find more?
Water supplies have been exhausted in many places
Where do we find more? How to treat waste water?
Croplands are replaced by homes and cities
Where can we grow croplands?
Waste, the products of our life style, must be put somewhere
Where do we put it and at what cost? How to recycle it?
Carrying Capacity, its ability to sustain its population at a basic, healthy,moderately comfortable standard of living
Have we exceeded it?
Global Warming, the activity of billions of people is impacting the climate ofearth
Can we reverse it?
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An Overview of Our Planetary Environment
Chapter 1
The solar system formed over 4.5 billion
years ago. The earth is unique among the
planets in its chemical composition,
abundant surface water, and oxygen-rich
atmosphere
The interaction between geologic
environments and our 6 million human
beings reshapes our planet
Image collage from NASA/JPL
Earth in space and time
Big Bang, the origin of todays universe
The Big Bang Theoryis the dominant scientific theory about the origin ofthe universe. Although the Big Bang Theory is widely accepted, it probablywill never be proved.
According to the big bang, the universe was created around 13.7 billionyears ago from a cosmic explosion that expulsed matter and in alldirections.
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Earth in space and time
Stars formed from the debris of the Big Bang. Local high concentrations ofmass were collected together by gravity and formed stars and planets.
The sun and its system of circling nine planets formed from a rotating cloudof gas and dust.
Most of the mass of the cloud coalesced to form the sun. Dust condensedfrom the gases remaining in the flattened cloud, and the dust clumped intoplanets.
astro.unl.edu
The compositions of the planets formed depended largely on how near theywere to the hot sun.
The nearest planets to the sun contained mainly metallic iron, a few veryhigh temperature minerals, and little water or gas. Farther from the sun, theplanets incorporated much larger amounts of low temperature minerals,liquid water, and condensed gases.
A series of planets with a variety of compositions was born.
Earth in space and time
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The planetary densities are consistent with a higher metal and rock content in the
four planets closest to the sun and a much larger proportion of ice and gas in the
planets farther from the sun.
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Third planet from the Sun
around 4.5 billion years old
Mean temperature 15 o C, not too hot or cold
Eight chemically distinct planets in our Solar System
Four rocky and metallic inner planets
Inner-most planets very hot (nearest the Sun)
Four gaseous outer planets
Outer planets very cold
Ninth planet, Pluto, is not considered a planet
Universe is over 13.7 billion years old
Earth in space and time
The planets of the solarsystem have different
composition and physical
properties
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Solar System
About 4.5 billion years ago, out of a swirling mass of gas and dust, evolved asystem of varied planets hurtling around a nuclear-powered star -- thesystem is our solar system.
Formed after the universe
Planets revolve around Sun
One complete trip for Earth equals one year
Earth at 23.5otilt from the vertical
Hemispheres of the Earth do not receive equal solar energy year round
Because of the tilt
Produces seasons
Earthcontinuous change
Early Eartha barren world with a cratered surface
lacked oceans
Lacked atmosphere
Earth heated up and was molten
Earth was target of many impacts
Asteroids Dust Particles
Meteors
Comets
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As cooling progressed, dense materials, such as metallic iron, would sinktoward the middle of the earth while lighter, low-density minerals
crystallized and floated out toward the surface.
Process: Differentiation of this world developed compositional zones
Central core:dense and hot
Composed of nickel (Ni) and iron (Fe)
Mantle: thick zone that surrounds the core
Composed of ultramafic and mafic rocks and magma
Heat from core escapes by convective circulation
Crust: chemically different from core or mantle
Two types of crust: Oceanic (mafic) and Crustal (felsic)
Water and atmospheric gases interact only with outermost crust
Earthcontinuous change
A chemically differentiated earth
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Table 1.02
Early Atmosphere The heating and subsequent differentiation of the early earth led to theformation of the atmosphere and oceans.
Many minerals that contained water or gases in their crystals released themduring the heating and melting, and as the earths surface cooled, the water
could condense to form the oceans and gases form the atmosphere.
Chemically different than today
No modern pollution
Lacked free oxygen (O2)
Dominated by nitrogen (N) and carbon dioxide (CO2)
Minor amounts of other gases:
Methane (CH4)
Ammonia (NH3)
Sulfur gases
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The geologic spiral
First Life on earth
Early atmosphere required modification before life could evolve
Single-celled blue-green algae flourished first
Abundant oxygen was required for other life
Photosynthesis by algae produced oxygen
Sunlight energized a chemical reaction in algae
Food was produced from CO2 Oxygen given off as a by-product
Oxygen accumulated in the atmosphere
Life for oxygen meant breathing organisms could evolve
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Life Evolves on Earth
Last 500 million years
Vertebrates appeared about 500 millionyears ago
Land plants appeared about 400 millionyears ago
Insects developed about 300 millionyears ago
Dinosaurs appeared about 230 millionyears ago
Birds appeared about 150 millionyears ago
Mammals and birds well established by 100 millionyears ago
Primitive human (hominids) beings appeared by 2 to 3 millionyears ago
Modern humans (homo sapiens) appear during last 20,000years