Transcript Chapter 1 Foundations

Chapter 1
An Overview of Our
Planetary Environment
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
Earth in space and time
• Big Bang, the origin of today’s universe
• The Big Bang Theory is the dominant
scientific theory about the origin of the
universe. Although the Big Bang
Theory is widely accepted, it probably
will never be proved.
• According to the big bang, the universe
was created sometime between 10
billion and 20 billion years ago from a
cosmic explosion that hurled matter
and in all directions.
Earth in space and time
• Stars formed from the debris of the Big
Bang. Local high concentrations of mass
were collected together by gravity and
formed stars and planets.
• The sun and its system of circling nine
planets formed from a rotating cloud of
gas and dust.
• Most of the mass of the cloud coalesced
to form the sun. Dust condensed from
the gases remaining in the flattened
cloud, and the dust clumped into
planets.
Earth in space and time
• The compositions of the planets formed
depended largely on how near they were
to the hot sun.
• The nearest planets to the sun contained
mainly metallic iron, a few very high
temperature minerals, and little water or
gas. Farther from the sun, the planets
incorporated much larger amounts of
low temperature minerals, liquid water,
and condensed gases.
• A series of planets with a variety of
compositions was born.
Figure 1.1 The distance scale is logarithmic
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.
Earth in space and time
• Third planet from the Sun
– over 4 billion years old
– Mean temperature 15 oC, not too hot or cold
• Nine 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, may not be a planet
• Universe is over 15-20 billion years old
Fig. 1.2 the planets
of the solar system
have different
composition and
physical properties
Solar System
• About five billion years ago, out of a swirling
mass of gas and dust, evolved a system of
varied planets hurtling around a nuclearpowered star -- the system is our solar
system.
• Formed after the universe
• Planets revolve around Sun
– One complete trip for Earth equals one year
– Earth at 23.5o tilt from the vertical
– Hemispheres of the Earth do not receive equal
solar energy year round
• Because of the tilt
• Produces seasons
Earth – continuous change
• Early Earth – a 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
Earth – continuous change
• As cooling progressed, dense materials, such as metallic
iron, would sink toward the middle of the earth while
lighter, low-density minerals crystallized and floated out
toward the surface.
• 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
Figure 1.3 A chemically differentiated earth
Table 1.02
Early Atmosphere
• The heating and subsequent differentiation of the early earth
led to the formation of the atmosphere and oceans.
• Many minerals that contained water or gases in their crystals
released them during the heating and melting, and as the
earth’s 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
• Barren of life
Figure 1.4 the geologic spiral
First Life
• 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
Life Evolves on Earth
Up to 500 million years ago
• Early life forms – little evidence
– no hard parts (no teeth, bones, shells, or claws)
• Earliest rocks – limited life forms, single-celled
organisms
– 2 billion years ago some rocks show evidence of
blue-green algae
• Multicelled creatures appear 1 billion years ago
– Oxygenated atmosphere developed
• Marine animals with shells widespread by 600
million years ago
Life Evolves on Earth
Last 500 million years
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Vertebrates appear about 500 million years ago
Land plants appear about 400 million years ago
Insects develop about 300 million years ago
Dinosaurs appear about 200 million years ago
Birds appear about 150 million years ago
Mammals and birds well established by 100
millions years ago
• Primitive human beings appear by 3 to 4
millions years ago
• Modern humans (Homo sapiens) appear during
last 500,000 years
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
more interdisciplinary science through time
– Starting materials that form rocks and minerals often are
completely changed during the course of time
• Time – seconds, minutes and hours are units of time
that are replaced by time intervals of thousands,
millions, or billions, of years
Scientific Method
A means to discover basic scientific principles
• Starting Point – a set of observations and/or a body of data
from measurements of phenomena and/or experiments
• Hypothesis is formed to explain the observations or data
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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
• Theory formed as accepted explanation for an observation
or set of data
– Hypothesis becomes a theory only after extensive testing of the
hypothesis
Theory versus Hypothesis
• Theory – accepted 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 Method
Geology has problems that other sciences do not!
• Problems with size
– A volcano is big
– 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
Why Environmental Geology?
• Environmental geology explores the many
and varied interactions between humans and
geologic environments
• Earth is a dangerous place!
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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
Figure 1.5
Figure 1.6
Figure 1.7
Figure 1.8
Figure 1.9
Population Growth
• Population has experienced exponential growth:
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Possibly 9 billion people by 2050
Slow population growth up until mid-19th century
Doubling times have become shorter
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
– AIDS epidemic
– Impacts dictated by economic, social, or religious
values
– Limited exploitation of new sources of natural resources
– Growing demand by third world countries wanting to
become first world countries
Figure 1.12
Figure 1.13
Impacts of the Human Population
• Rapid growth of humans results in problems
obtaining an adequate food supply
• Expect problems with maintaining adequate:
– Water supplies 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
– Our ever expanding, high energy, and resource
consuming life styles
– Genetic engineering contributes to food
production
Figure 1.14 Population distribution by region in
2002 with projection to the year 2050
Figure 1.17 Global population density; the darker
the shading, the higher the population density.
Impacts of the Human Population
How do we resolve the issues?
What consequences will we face because of our
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?
– Croplands are replaced by homes and cities
• Where do we find more?
– Waste, the products of our life style, must be put
somewhere
• Where do we put it and at what cost?
– 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 of earth
• Can we reverse it?