Go back to Tasa Portfolio Volume 1

The images on Tasa Portfolio Volume 1 are related to these subjects:

Matter and Minerals
Igneous Rocks
Volcanic Activity
Weathering and Soil
Sedimentary Rocks
Metamorphic Rocks
Geologic Time
Mass Wasting

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The geologic time scale. Numbers on the time scale represent time in 
millions of years before the present. These dates were added long after 
the time scale had been established using relative dating techniques. The 
Precambrian accounts for about 88 percent of geologic time. (Data from 
Geological Society of America)

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Viewed over long spans, rocks are constantly forming, changing, and 
reforming. The rock cycle helps us understand the origin of the three 
basic rock groups. Arrows represent processes that link each group to the 
others.

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Major physical features of the continents and ocean basins. The diversity 
of features on the ocean floor is as varied as on the continents.

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Nebular hypothesis. A. A huge rotating cloud of dust and gases (nebula) 
begins to contract. B. Most of the material is gravitationally swept 
toward the center, producing the Sun. However, owing to rotational motion, 
some dust and gases remain orbiting the central body as a flattened disk. 
C. The planets begin to accrete from the material that is orbiting within 
the flattened disk. D. In time most of the remaining debris was either 
collected into the nine planets and their moons or swept out into space by 
the solar wind.

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Views of Earth's layered structure. The left side of the large cross 
section shows that Earth's interior is divided into three different layers 
based on compositional differences - the crust, mantle, and core. The 
right side of the large cross section depicts the five main layers of 
Earth's interior based on physical properties and hence mechanical 
strength - the lithosphere, asthenosphere, mesosphere, outer core, and 
inner core. The block diagrams above the large cross section show an 
enlarged view of the upper portion of Earth's interior.

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Mosaic of rigid plates that constitute Earths outer shell. (After W. B. 
Hamilton, U.S. Geological Survey)

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View of Earth showing the relationship between divergent, convergent, and 
transform fault boundaries.

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When two plates containing continental lithosphere collide, complex 
mountains are formed. The formation of the Himalayas represents a 
relatively recent example.

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Most rocks are aggregates of several kinds of minerals. (Photos by E. J. 
Tarbuck)

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Two models of the atom. A. A very simplified view of the atom, which 
consists of a central nucleus, consisting of protons and neutrons, 
encircled by high-speed electrons. B. Another model of the atoms showing 
spherically shaped electron clouds (energy level shells). Note that these 
models are not drawn to scale. Electrons are minuscule in size compared to 
protons and neutrons, and the relative space between the nucleus and 
electron shells is much greater than illustrated.

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Chemical bonding of sodium and chlorine through the transfer of the lone 
outer electron from a sodium atom to a chlorine atom. The result is a 
positive sodium ion (Na+) and a negative chloride ion (Cl-). Bonding to 
produce sodium chloride (NaCl) is due to electrostatic attraction between 
the positive and negative ions. In this process note that both the sodium 
and chlorine atoms have achieved the stable noble-gas configuration (eight 
electrons in their outer shell).

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Schematic diagrams illustrating the arrangement of sodium and chloride 
ions in table salt. A. Structure has been opened up to show arrangement of 
ions. B. Actual ions are closely packed.

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Illustration of the sharing of a pair of electrons between two chlorine 
atoms to form a chlorine molecule. Notice that by sharing a pair of 
electrons, both chlorine atoms have eight electrons in their valence shell.

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Ideal geometrical packing for various-sized positive and negative ions.

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Comparing the structures of diamond and graphite. Both are natural 
substances with the same chemical composition-carbon atoms. Nevertheless, 
their internal structure and physical properties reflect the fact that 
each formed in a very different environment. A. All carbon atoms in 
diamond are covalently bonded into a compact, three-dimensional framework, 
which accounts for the extreme hardness of the mineral. B. In graphite the 
carbon atoms are bonded into sheets that are joined in a layered fashion 
by very weak electrical forces. These weak bonds allow the sheets of 
carbon to readily slide past each other, making graphite soft and 
slippery, and thus useful as a dry lubricant.

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Two representations of the silicon-oxygen tetrahedron. A. The four large 
spheres represent oxygen ions, and the blue sphere represents a silicon 
ion. The spheres are drawn in proportion to the radii of the ions. B. An 
expanded view of the tetrahedron using rods to depict the bonds that 
connect the ions.

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Relative sizes and electrical charges of ions of the eight most common 
elements in Earth's crust. These are the most common ions in rock-forming 
minerals. Ionic radii are expressed in angstroms (1 angstrom equals 10(-8) 
cm).

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Three types of silicate structures.  A. Single chains. B. Double chains. 
C. Sheet structures.

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Common silicate minerals. Note that the complexity of the silicate 
structure increases down the chart.

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Cleavage angles for augite and hornblende.

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Mineralogy of common igneous rocks and the magmas from which they form. 
(After Dietrich, Daily, and Larsen)

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Classification of the major groups of igneous rocks based on their mineral 
composition and texture. Phaneritic (coarse-grained) rocks are plutonic, 
solidifying deep underground. Aphanitic (fine-grained) rocks are volcanic, 
or solidified as shallow, thin plutons.

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As hot mantle rock ascends, it continually moves into zones of lower 
pressure. This drop in confining pressure can trigger melting, even 
without additional heat.

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As an oceanic plate descends into the mantle, water and other volatiles 
are driven from the subducting crustal rocks. These volatiles lower the 
melting temperature of mantle rock sufficiently to generate melt.

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Bowen's reaction series shows the sequence in which minerals crystallize 
from a magma. Compare this figure to the mineral composition of the rock 
groups. Note that each rock group consists of minerals that crystallize in 
the same temperature range.

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Illustration of how a magma evolves as the earliest-formed minerals (those 
richer in iron, magnesium, and calcium) crystallize and settle to the 
bottom of the magma chamber, leaving the remaining melt richer in sodium, 
potassium and silica. A. Emplacement of a magma body and associated 
igneous activity generates rocks having a composition similar to that of 
the initial magma. B. After a period of time, crystallization and settling 
changes the composition of the melt, while generating rocks having a 
composition quite different than the original magma. C. Further magmatic 
differentiation results in another more highly evolved melt with its 
associated rock types.

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A. Emplacement of a magma body and associated igneous activity generates 
rocks having a composition similar to that of the initial magma.

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B. After a period of time, crystallization and settling changes the 
composition of the melt, while generating rocks having a composition quite 
different than the original magma.

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C. Further magmatic differentiation results in another more highly evolved 
melt with its associated rock types.

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This illustration show three ways that the composition of a magma body may 
be altered: magma mixing; assimilation of host rock; and crystallization 
and settling (magmatic differentiation).

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Idealized diagrams showing the events in the May 18, 1980, eruption of 
Mount St. Helens. A. First, a sizable earthquake recorded on Mount St. 
Helens indicates that renewed volcanic activity is possible. B. Alarming 
growth of a bulge on the north flank suggests increasing magma pressure 
below. C. Triggered by an earthquake, a giant landslide reduced the 
confining pressure on the magma body and initiated an explosive lateral 
blast. D. Within seconds a large vertical eruption sent a column of 
volcanic ash to an altitude of about 18 kilometers (11 miles). This phase 
of the eruption continued for over nine hours.

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Anatomy of a "typical" composite cone.

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Shield volcanoes are built primarily of fluid basaltic lava flows and 
contain only a small percentage of pyroclastic materials.

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Profiles of volcanic landforms. A. Profile of Mauna Loa, Hawaii, the 
largest shield volcano in the Hawaiian chain. Note size comparison with 
Mt. Rainier, Washington, a large composite cone. B. Profile of Mt. 
Rainier, Washington. Note how it dwarfs a typical cinder cone. C. Profile 
of Sunset, Arizona, a typical steep-sided cinder cone.

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Cinder cones are built from ejected lava fragments that take on the 
appearance of cinders or clinkers as they begin to harden while in flight.

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Of the 13 potentially active volcanoes in the Cascade Range, 11 have 
erupted in the past 4000 years and 7 in just the past 200 years. More than 
100 eruptions, most of which were explosive, have occurred in the past 
4000 years. Mount St. Helens is the most active volcano in the Cascades. 
Its eruptions have ranged from relatively quiet outflows of lava to 
explosive events much larger than that of May 18, 1980. Each eruption 
symbol in the diagram represents from one to several dozen eruptions 
closely spaced in time. (After U.S. Geological Survey)

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Map showing the remains of the volcanic island of Santorini after the top 
of the cone collapsed into the emptied magma chamber following an 
explosive eruption. The location of the recently excavated Minoan town of 
Akrotiri is shown. Volcanic eruptions over the last 500 years built the 
central islands. Despite the fact that another destructive eruption is 
likely, the city of Phira was built on the flanks of the caldera.

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Sequence of events that formed Crater Lake, Oregon. About 7000 years ago, 
a violent eruption partly emptied the magma chamber, causing the summit of 
former Mount Mazama to collapse. Rainfall and groundwater contributed to 
form Crater Lake, the deepest lake in the United States. Subsequent 
eruptions produced the cinder cone called Wizard Island. (After H. 
Williams, The Ancient Volcanoes of Oregon, p. 47. Courtesy of the 
University of Oregon)

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Volcanic areas that compose the Columbia Plateau in the Pacific Northwest. 
The Columbia River basalts cover an area of nearly 200,000 square 
kilometers (80,000 square miles). Activity here began about 17 million 
years ago as lava began to pour out of large fissures, eventually 
producing a basalt plateau with an average thickness of more than 1 
kilometer. (After U.S. Geological Survey)

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Basaltic fissure eruption. Lava fountaining from a fissure and formation 
of fluid lava flows called flood basalts.

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Illustrations showing basic igneous structures. A. This block diagram 
shows the relationship between volcanism and intrusive igneous activity. 
B. This view illustrates the basic intrusive igneous structures, some of 
which have been exposed by erosion long after their formation. C. After 
millions of years of uplifting and erosion, a batholith is exposed at the 
surface.

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A. This block diagram shows the relationship between volcanism and 
intrusive igneous activity.

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B. This view illustrates the basic intrusive igneous structures, some of 
which have been exposed by erosion long after their formation.

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C. After millions of years of uplifting and erosion, a batholith is 
exposed at the surface.

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Granitic batholiths that occur along the western margin of North America. 
These gigantic, elongated bodies consist of numerous plutons that were 
emplaced during the last 150 million years of Earth history.

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Locations of some of Earth's major volcanoes.

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Three zones of volcanism. Two of these zones are plate boundaries, and the 
third is the interior area of the plates.

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Convergent plate volcanism.

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Divergent plate volcanism.

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Intraplate volcanism.

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As an oceanic plate descends into the mantle, water and other volatiles 
are driven from the subducting crustal rocks. These volatiles lower the 
melting temperature of mantle rock sufficiently to generate melt.

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Model of a mantle plume and associated hot-spot volcanism. A. A rising 
mantle plume with large bulbous head and narrow tail. B. Rapid 
decompression melting of the head of a mantle plume produces vast 
outpourings of basalts. C. Less voluminous activity caused by the plume 
tail produces a linear volcanic chain on the seafloor.

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Chemical weathering can occur only to those portions of a rock that are 
exposed to the elements. Mechanical weathering breaks rock into smaller 
and smaller pieces, thereby increasing the surface area available for 
chemical attack.

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Sheeting is caused by the expansion of crystalline rock as erosion removes 
the overlying material. When the deeply buried pluton in A is exposed at 
the surface following uplift and erosion in B, the igneous mass fractures 
into thin slabs.

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Illustration of halite dissolving in water. A. Sodium and chloride ions 
are attacked by the polar water molecules. B. Once removed, these ions are 
surrounded and held by a number of water molecules as shown.

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Spheroidal weathering of extensively jointed rock.  Water moving through 
the joints begins to enlarge them. Because the rocks are attacked more on 
the corners and edges, they take on a spherical shape. The photo shows 
spheroidal weathering in Joshua Tree National Monument, California. (Photo 
by E. J. Tarbuck)

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The weathering of common silicate minerals. The order in which the 
silicate minerals chemically weather is essentially the same as their 
order of crystallization.

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Composition (by volume) of a soil in good condition for plant growth. 
Although the percentages vary, each soil is composed of mineral and 
organic matter, water, and air.

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The parent material for residual soils is the underlying bedrock, whereas 
transported soils form on unconsolidated deposits. Also note that as 
slopes become steeper, soil becomes thinner. (Photos by E. J. Tarbuck)

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Idealized soil profile from a humid climate in the middle latitudes.

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Simplified diagram of the carbon cycle, with emphasis on the flow of 
carbon between the atmosphere and the hydrosphere, lithosphere, and 
biosphere. The colored arrows show whether the flow of carbon is into or 
out of the atmosphere.

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Successive stages in the formation of coal. (Photos by E. J. Tarbuck)

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Sedimentary environments are those places where sediment accumulates. Each 
is characterized by certain physical, chemical, and biological conditions. 
Because each sediment contains clues about the environment in which it was 
deposited, sedimentary rocks are important in the interpretation of Earth 
history. A number of important continental, transitional, and marine 
sedimentary environments are represented in this idealized diagram.

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When a single sedimentary layer is traced laterally, we may find that it 
is made up of several different rock types. This can occur because many 
sedimentary environments can exist at the same time over a broad area. The 
term facies is used to describe such sets of sedimentary rocks. Each 
facies grades laterally into another that formed at the same time but in a 
different environment.

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Graded beds. Each layer grades from coarse at its base to fine at the top.

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Pressure (stress) as a metamorphic agent. A. In a depositional 
environment, as confining pressure increases, rocks deform by decreasing 
in volume. B. During mountain building, rocks subjected to differential 
stress are shortened in the direction that pressure is applied, and 
lengthened in the direction perpendicular to that force.

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Mechanical rotation of platy or elongated mineral grains. A. Existing 
mineral grains keep their random orientation if force is uniformly 
applied. B. As differential stress causes rocks to flatten, mineral grains 
rotate toward the plane of flattening.

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Development of preferred orientations of minerals such as quartz, calcite, 
and olivine. A. Ductile deformation (flattening) of these roughly 
equidimensional mineral grains can occur in one of two ways. B. The first 
mechanism is a solid-state plastic flow that involves intracrystalline 
gliding of individual units within each grain. C. The second mechanism 
involves dissolving material from areas of high stress and depositing that 
material in locations of low stress. D. Both mechanisms change the shape 
of the grains, but the volume and composition of each grain remains 
essentially unchanged.

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Development of one type of rock cleavage. As shale is strongly folded (A., 
B.) and metamorphosed to form slate, the developing mica flakes are bent 
into microfolds. C. Further metamorphism results in the recrystallization 
of mica grains along the limbs of these folds to enhance the foliation. D. 
Hand sample of slate illustrates rock cleavage and its orientation to 
relic bedding surfaces.

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Classification of common metamorphic rocks.

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Contact metamorphism produces a zone of alteration called an aureole 
around an intrusive igneous body.

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Idealized illustration of progressive regional metamorphism. From left to 
right, we progress from low-grade metamorphism (slate) to high-grade 
metamorphism (gneiss). (Photos by E. J. Tarbuck)

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The typical transition in mineralogy that results from progressive 
metamorphism of shale.

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Zones of metamorphic intensities in New England.

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Metamorphic environments according to the plate tectonics model.

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Occurrences of metamorphic rocks. The continental shields of the world are 
composed largely of metamorphic rocks and associated igneous intrusions. 
In addition, the deformed portions of many mountain belts are also 
metamorphic. The remaining area shown in this map is the stable 
continental interior, which generally consists of undeformed sedimentary 
beds that overlie metamorphic and igneous basement rocks.

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Applying the law of superposition to these layers exposed in the upper 
portion of the Grand Canyon, the Supai Group is oldest and the Kaibab 
Limestone is youngest. (Photo by E. J. Tarbuck)

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Cross-cutting relationships represent one principle used in relative 
dating. An intrusive rock body is younger than the rocks it intrudes. A 
fault is younger than the rock layers it cuts.

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These three diagrams illustrate one way that inclusions can form, and a 
type of unconformity termed a nonconformity. In the third diagram we know 
the igneous rock must be older because pieces of it are included in the 
overlying sedimentary bed. When older intrusive igneous rocks are overlain 
by younger sedimentary layers, a nonconformity is said to exist.

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This cross-section through the Grand Canyon illustrates the three basic 
types of unconformities. An angular unconformity can be seen between the 
tilted Precambrian Unkar Group and the Cambrian Tapeats Sandstone. Two 
disconformities are marked, above and below the Redwall Limestone. A 
nonconformity occurs between the igneous and metamorphic rocks of the 
Inner Gorge and the sedimentary strata of the Unkar Group.

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Formation of an angular unconformity. An angular unconformity represents 
an extended period during which deformation and erosion occurred.

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Geologic cross-section of a hypothetical region.

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Geologic cross-section of a hypothetical region.

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Correlation of strata at three locations on the Colorado Plateau reveals 
the total extent of sedimentary rocks in the region. (After U.S. 
Geological Survey; Photos by E. J. Tarbuck)

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Overlapping ranges of fossils help date rocks more exactly than using a 
single fossil.

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Common types of radioactive decay. Notice that in each case the number of 
protons (atomic number) in the nucleus changes, thus producing a different 
element.

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The most common isotope of uranium (U-238) is an example of a radioactive 
decay series. Before the stable end product (Pb-206) is reached, many 
different isotopes are produced as intermediate steps.

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The radioactive decay curve shows change that is exponential. Half of the 
radioactive parent remains after one half-life. After a second half-life 
one-quarter of the parent remains, and so forth.

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Cross dating is a basic principle in dendrochronology. Here it was used to 
date an archaeological site by correlating tree-ring patterns for wood 
from trees of three different ages. First, a tree-ring chronology for the 
area is established using cores extracted from living trees. This 
chronology is extended further back in time by matching overlapping 
patterns from older, dead trees. Finally, cores taken from beams inside 
the ruin are dated using the chronology established from the other two 
sites.

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A. Production and B. decay of carbon-14. These sketches represent the 
nuclei of the respective atoms.

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The geologic time scale. The numerical dates were added long after the 
time scale had been established using relative dating techniques. (Data 
from Geological Society of America)

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Numerical dates for sedimentary layers are usually determined by examining 
their relationship to igneous rocks. (After U.S. Geological Survey)

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A block diagram of a hypothetical area in the American Southwest. Place 
the lettered features in the proper sequence, from oldest to youngest. 
Identify an angular unconformity and a nonconformity.

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The four processes illustrated here are all considered to be relatively 
rapid forms of mass wasting. Because material in A. slumps and B. 
rockslides move along well-defined surfaces, they are said to move by 
sliding. By contrast, when material moves downslope as a viscous fluid, 
the movement is described as a flow. C. Debris flow and D. earthflow 
advance downslope in this manner.

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Slump occurs when material slips downslope en masse along a curved surface 
of rupture. Earthflows frequently form at the base of the slump.

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Parts A and B show a before and after cross-sectional view of the Gros 
Ventre rockslide. The slide occurred when the tilted and undercut 
sandstone bed could no longer maintain its position atop the saturated bed 
of clay. (After W. C. Alden, "Landslide and Flood at Gros Ventre, 
Wyoming," Transactions (AIME) 76 (1928); 348.)

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The repeated expansion and contraction of the surface material causes a 
net downslope migration of rock particles-a process called creep.

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Although creep is an imperceptibly slow movement, its effects are often 
visible.

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Distribution of permafrost in the Northern Hemisphere. More than 80 
percent of Alaska and about 50 percent of Canada are underlain by 
permafrost. Two zones are recognized. In the continuous zone, the only 
ice-free areas are beneath deep lakes or rivers. In the higher latitude 
portions of the discontinuous zone, there are only scattered islands of 
thawed ground. Moving southward, the percentage of unfrozen ground 
increases until all the ground is unfrozen. (After the U.S. Geological 
Survey)

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This building, located south of Fairbanks, Alaska, subsided because of 
thawing permafrost. Notice that the right side, which was heated, settled 
much more than the unheated porch on the left.