Download Earth in space and time

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.
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.
• Obviously, formed after the universe
• Planets revolve around Sun
– One complete trip for Earth equals one year
– Earth at 23.5o tilt from the vertical
– Because of the tilt
• Hemispheres of the Earth do not receive equal
solar energy year round
• Produces the seasons
Figure 1.2
Table 1.1
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.
Planet
Size
Earth=1
Avg Dist to
Sun
Rotation
Million
miles
MERCURY
.338
36
58.6 days
88
0
VENUS
.94
67
243 days
224.7
0
EARTH
1.0
93
23hr 56m
365.26
1
MARS
.53
142
24hr 37m
687 days
2
JUPITER
11.19
483
9hr 50m
11.86 yrs
16
SATURN
9.41
886
10hr 2m
29.46
17
URANUS
4.4
1783
10hr 48m
84 yrs
15
NEPTUNE
3.8
2791
15hr 48m
164.8 yrs
2
PLUTO
.4
3671
6hr 24m
248 yrs
1
Revolution
# of
moons
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
Figure 1.3
• Mercury
• Mars
• Jupiter
Figure 1.13 A
– The figure shows a region about 52 feet across occupied by a human being, a
sidewalk, and a few trees—all objects whose
size you can understand.
• Each successive picture in the chapter will
show you a region of the universe that is
100 times wider than the preceding
picture.
– That is, each step will widen your field of view—the
region you can see in the image—by a factor of 100.
In this figure, your field of view widens by a factor of 100, and
you can see an area 1 mile in diameter.
– The arrow points to the scene shown in the preceding photo.
– People, trees, and sidewalks
have vanished, but now you
can see a college campus
and the surrounding
streets and houses.
– The dimensions of houses
and streets are familiar.
This is the world you know,
and you can relate such
objects to the scale of your body.
• You started your adventure using feet
and miles, but you should use the metric
system of units.
– Not only is it used by all scientists around the world,
but it makes calculations much easier.
• The photo in the figure is 1 mile in diameter.
– A mile equals 1.609 kilometers.
– So, you can see in the photo that a kilometer is a bit over two-thirds of a mile—
a short walk across
a neighborhood.
• The view in this figure spans 160 kilometers.
– In this infrared photo, the green foliage shows up as various shades of red.
– The college campus is now invisible.
– The patches of gray are
small cities, with Wilmington,
Delaware, visible at the
lower right.
• At this scale, you see the natural features of Earth’s
surface.
– The Allegheny Mountains of southern Pennsylvania cross the image in the
upper left.
– The Susquehanna River flows southeast into Chesapeake Bay.
– What look like white bumps
are a few puffs of clouds.
• Notice the red color.
– This is an infrared photograph in which healthy green leaves and crops show up as red.
– Human eyes are sensitive to only a narrow range of colors.
– As you explore the universe,
you will learn to use a wide
range of ‘colors’—from
X rays to radio waves—to
reveal sights invisible to
unaided human eyes.
• At the next step in your journey, you will see your entire planet—which is
12,756 km in diameter.
• Earth rotates on its axis once a day, exposing half of its
surface to daylight at
any particular moment.
– The photo shows most of the
daylight side of the planet.
– The blurriness at the
extreme right is the sunset
line.
• The rotation of Earth carries you eastward.
– As you cross the sunset line into darkness, you say the sun has set.
• It is the rotation of the
planet that causes the
cycle of day and night.
• Enlarge your field of view by a factor of 100, and you will see a
region 1,600,000 km wide.
– Earth is the small blue dot in the center.
– The moon—whose diameter
is only one-fourth that of
Earth—is an even smaller dot
along its orbit 380,000 km
from Earth.
– These numbers are so large
that it is inconvenient to
write them out.
– This is nothing more than a simple way to write numbers
without writing lots of zeros.
– In scientific notation, you would write 380,000 as 3.8 x
105.
– The universe is too big to discuss without using scientific
notation.
• When you once again enlarge your field of view by a factor of 100, Earth,
the moon, and the moon’s orbit all lie in the small red box at lower left.
– Now, however, you can see
the sun and two other
planets that are part of our
solar system.
– Our solar system consists of
the sun, its family of planets,
and some smaller bodies
such as moons and comets.
• Like Earth, Venus and Mercury are planets—small, nonluminous bodies that shine by reflected light.
– Venus is about the size of
Earth and Mercury is
a bit larger than
Earth’s moon.
– On this diagram, they
are both too small to
be seen as anything
but tiny dots.
• The sun is a star—a self-luminous ball of hot gas that generates
its own energy.
– The sun is 109 times larger in diameter than Earth, but it too is nothing more than a dot in
the diagram.
• This diagram has a diameter of 1.6 x 108 km.
– The average distance from Earth to the sun is a unit of distance called the
astronomical unit (AU),
a distance of 1.5 x 1011 m.
• Using this unit, you can say that the average distance from
Venus to the sun is about 0.7 AU.
• The average distance from Mercury to the sun is about 0.39
AU.
• The orbits of the planets are not perfect circles, and this is
particularly apparent for Mercury.
– Its orbit carries it as close to the sun as 0.307 AU and
as far away as 0.467 AU.
– You can see this variation in
the distance from Mercury
to the sun in the figure.
– Earth’s orbit is more circular,
and its distance from the
sun varies by only a few
percent.
• Enlarge your field of view again, and you can see the entire solar system.
• The details of the preceding figure are now lost in the red square at the
center of the diagram.
– You see only the brighter,
more widely separated
objects.
• The sun, Mercury, Venus, and Earth lie so close together that you cannot
separate them at this scale.
• Mars, the next outward planet, lies only 1.5 AU from the sun.
• In contrast, Jupiter, Saturn, Uranus, Neptune, and Pluto are so
far from the sun that they are easy to place in the diagram.
– These are cold worlds far
from the sun’s warmth.
– Light from the sun reaches
Earth in only 8 minutes,
but it takes over 4 hours to
reach Neptune.
• Pluto’s orbit is so elliptical that it can come closer to
the sun than Neptune does—as Pluto did between
1979 and 1999.
• When you again enlarge your field of view by a factor
of 100, the solar system vanishes.
– The sun is only a point of light, and all the planets and their orbits are now
crowded
into the small red square
at the center.
– The planets are too small
and reflect too little light
to be visible so near the
brilliance of the sun.
• Nor are any stars visible except for the sun.
– The sun is a fairly typical star, and it seems to be located in a fairly average
neighborhood in the universe.
– Although there are many
billions of stars like the sun,
none is close enough to be
visible in the diagram—
which shows an area only
11,000 AU in diameter.
• The stars are typically separated by distances about 10
times larger than the diameter of the diagram.
– Except for the sun at the center, this diagram is empty.
• Now, your field of view has expanded to a diameter a
bit over 1 million AU.
– The sun is at the center,
and you can see a few
of the nearest stars.
– These stars are so distant
that it is not reasonable
to give their distances in
astronomical units.
• To express distances so large, define a
new unit of distance—the light-year.
– One light-year (ly) is the distance that light travels in
one year—roughly 1013 km or 63,000 AU.
•
It is a common misconception that a
light-year is a time.
– Have you heard people say, “It will take me light-years
to finish my term paper”?
– Next time, you can tell them that a light-year is a
distance, not a time.
• The diameter of your field of view in the figure is 17 ly.
• The nearest star to the sun, Alpha Centauri, is 4.2 ly from Earth.
– In other words, light from
Alpha Centauri takes
4.2 years to reach Earth.
• In the figure, the sizes of the dots represent not the sizes of the
stars but their brightness.
– This is the custom in astronomical diagrams, and it is also how star images are
recorded on photos.
– Bright stars make larger
spots on a photo than faint
stars.
– The size of a star image in a
photo informs you not how
big the star is but only how
bright it looks.
• Now, you expand your field of view by another factor of 100,
and the sun and its neighboring stars vanish into the
background of thousands of other stars.
– The field of view is
1,700 ly in diameter.
• Of course, no one has ever journeyed thousands of light-years to
photograph the solar neighborhood.
– So, this is a representative photo of the sky.
• The sun is a relatively
faint star that would
not be easily located
in a photo at this
scale.
• If you expand your field of view by a factor of 100, you see our
galaxy—a disk of stars about 75,000 ly in diameter.
– A galaxy is a great cloud of stars, gas, and dust bound together by the combined
gravity of all the matter.
– Galaxies range from
1,500 to over 300,000 ly
in diameter and can
contain over 100 billion
stars.
• As you expand your field of view by another factor of 100, our
galaxy appears as a tiny luminous speck surrounded by other
specks.
– The diagram includes a
region 17 million ly in
diameter, and each of the
dots represents a galaxy.
– Notice that our galaxy is
part of a cluster of a few
dozen galaxies.
• If you again expand your field of view, you see that the clusters of
galaxies are connected in a vast network.
– Clusters are grouped into superclusters—clusters of clusters.
– The superclusters are linked
to form long filaments and
walls outlining voids that
seem nearly empty of
galaxies.
– These appear to be the
largest structures in the
universe.
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, lowdensity 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 1.4 A chemically differentiated earth
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
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
– oxygen meant breathing organisms could
evolve
Figure 1.5: The geologic spiral
Life 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 on Earth
Last 500 million years
•
•
•
•
•
•
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 million
years ago
• Primitive human beings appear by 3 to 4 million years
ago
• Modern humans (Homo sapiens) appear during last
90,000 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
• Geology is an environmental science
– Rocks record how earth has changed over time
– Control of erosion and sedimentation required under Clean Water Act
– Recognition and mitigation of natural hazards
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
– An 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 1.6 1995 Kobe Earthquake
Figure 1.7 May 1980, Mt St. Helens
Figure 1.8 1993 Mississippi Floods
Figure 1.9 California landslides
Figure 1.12
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
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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 1.13 World Population
Impacts of the Human Population
• Rapid growth of humans results in problems
obtaining an adequate food supply
• Expect problems with maintaining adequate:
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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 1.15 Population distribution by region in 2002
with projection to the year 2050
Figure 1.18 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?