What is the earth systems and what are the processes and interaction.

Contributed by:

kevin Mon, Jan 17, 2022 09:38 PM UTC

The term “Earth system" refers to Earth´s interacting physical, chemical, and biological processes. The system consists of the land, oceans, atmosphere, and poles.

1. CHAPTER
3
Earth Systems:
Processes and
Interactions
Major Concepts and Questions Addressed in This Chapter
A What is the rock cycle, and how is it related to plate F How do the atmosphere and continental configuration
tectonics and the tectonic cycle? affect ocean circulation?
B What are the major types of rocks, and how do we infer G What accounts for the distribution and diversity of
how and where they formed? plants and animals over Earth’s surface?
C What are the major patterns of atmospheric H How is the availability of energy related to the structure
circulation? of biologic communities?
D How does atmospheric circulation affect the I How are nutrients and other elements recycled, and
distribution of heat and moisture over Earth’s surface? why is nutrient recycling important?
E How fast do the oceans circulate? J How has the tectonic cycle affected the atmosphere
and hydrosphere?
Chapter Outline
3.1 The Solid Earth System: Components and 3.3 Atmosphere and Its Circulation
Processes BOX 3.1 Asian Monsoon: Influence of Large Land
3.2 Rock Cycle Masses on Atmospheric Circulation and the
3.2.1 Igneous rocks Hydrologic Cycle
Intrusive igneous rocks: occurrence, texture, 3.4 The Hydrosphere
and composition 3.4.1 Hydrologic cycle
Extrusive igneous rocks: occurrence, texture, 3.4.2 Ocean circulation
and composition
3.5 The Biosphere
How do different kinds of magmas form?
3.5.1 Biogeography: distribution of plants and
3.2.2 Sedimentary rocks animals over Earth’s surface
3.2.3 Metamorphic rocks 3.5.2 Energy relationships
Metamorphic rocks: texture and mineralogy 3.5.3 Biogeochemical cycles
Types of metamorphism 3.6 The Tectonic Cycle and Earth Systems
Yellowstone Gorge, Yellowstone National Park, Wyoming. The bright colors of the rocks result from lava flows and ash falls.
© Filip Fuxa/Shutterstock, Inc.
56
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 56 07/11/16 5:28 pm

2. The Solid Earth System:
3.1 3.2 Rock Cycle
Components and Processes The major cycle operating within the solid Earth sys-
B tem, especially the lithosphere, is the rock cycle
Chapter 3 examines each of Earth’s major systems in
A greater detail. As we proceed, recall the basic features (Figure 3.1). The rock cycle involves the formation and
destruction of the three major rock types, or lithologies: igne-
of natural systems introduced in Chapter 1: (1) each major ous, sedimentary, and metamorphic. Igneous rocks are
Earth system consists of a series of parts or compartments those that have cooled and solidified from magma (from the
that comprise a larger integrated and complex whole, Latin, for “characterized by fire”).
(2) each system is an open system that exchanges matter and In an idealized example of the rock cycle, igneous
energy with the environment, and (3) each system behaves rocks erode to produce sedimentary rocks that are later
in a cyclic manner because of the flow of matter and energy metamorphosed and then melted to produce igneous rocks
through the system. (Figure 3.1). Usually, though, the rock cycle does not func-
The flows of matter and energy within and between tion this simply. Depending on conditions, all preexisting
systems are known as fluxes. This chapter emphasizes two rocks, whether they are igneous, sedimentary, or metamor-
major features of the fluxes of matter and energy: phic, can be subjected to any one or more of the processes
1. Fluxes of matter and energy within systems and between of the rock cycle out of this sequence. Igneous rocks can,
systems are cyclic. for example, be metamorphosed without first having been
2. Systems interact with one another through the fluxes of eroded; metamorphic rocks can erode to produce sedimen-
matter and energy. tary rocks; sedimentary rocks can be metamorphosed; or
sedimentary rocks can become caught up in a “sedimentary
Recall, for example, that plate tectonics is driven by loop” in which they are recycled through the processes of
the flow of heat, which is itself produced by radioactive erosion, transport, deposition, and lithification all over again
decay (Chapter 2). We will concentrate on how plate tec- to produce new sedimentary rocks.
tonics interacts with each of the other major Earth systems
beginning with the rock cycle, and then move on to the
behavior of the modern atmosphere, the hydrosphere, and
3.2.1 Igneous rocks
biosphere. This will allow us to then examine how the tec-
Intrusive igneous rocks: occurrence, texture,
tonic cycle has broadly influenced the other systems through
geologic time. and composition
Intrusive igneous rocks form beneath Earth’s surface. Bodies
of solidified magma beneath Earth’s surface are referred to as
plutons and vary substantially in size and shape. Gigantic
plutons are called batholiths, whereas smaller dome-shaped
Sediments Sedimentary rocks
Lithification
Sedimentary
beds
Erosion Erosion
Metamorphism Transport
Deposition
Uplift
Sedimentary beds
Compression
Igneous Metamorphic Lithospheric
rocks Magma rocks plate
Crystalization Melting
Intrusion
(a) (b)
Data from: Hawkesworth, C. J., and A. I. A. Kemp. 2006. Nature, 443, 811–817.
FIGURE 3.1 The rock cycle in relation to plate tectonics. The rock cycle involves the formation of molten magma and its intrusion into
surrounding rocks or extrusion onto the Earth’s surface as volcanoes; uplift, weathering and erosion, and redeposition to form sedimentary
rocks; and metamorphism of preexisting rocks. Note the similarity of plate tectonics and the rock cycle.
3.2 Rock Cycle 57
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 57 07/11/16 5:28 pm

3. ones are called laccoliths (Figure 3.2). The dome shape of Although no one has ever seen an intrusive igneous
laccoliths occurs because the magma is still relatively thick rock form, their emplacement beneath Earth’s surface can
and tends to collect in one spot, resulting in an igneous be inferred from their coarse-grained, or phaneritic, texture
body with a relatively flat base and domed upper surface. (“phaneritic” means visible, referring to the visible mineral
Intrusive rocks can also occur as relatively thin bodies cut- faces in the rock). The term texture refers to the size, shape,
ting across surrounding rocks (dikes) or injected parallel to and arrangement of the grains in a rock. Phaneritic textures
strata (sills). One of the most spectacular sills is the Pali- occur when minerals in the rock exhibit relatively large,
sades Sill, located along the Hudson River, north of New blocky mineral faces that make them easily visible. This hap-
York City; the Palisades are composed primarily of igneous pens when the flux of heat from the magma to the surround-
rocks emplaced as the supercontinent Pangaea rifted apart ing environment occurs very slowly, giving the crystal faces
(Figure 3.3). sufficient time to grow into visible surfaces (Figure 3.4).
Active Recent Cinder
volcanism lava flows cone Laccolith
Volcano
Dike
Sill
Magma chamber
Batholith
(a) Reproduced from: U.S. Geological Survey (http://pubs.usgs.gov/of/2004/1007/volcanic.html). Accessed April 27, 2011.
(b) Courtesy of Dr. Allan Thompson, University of Delaware.
FIGURE 3.2 (a) Intrusive igneous rock bodies: batholiths, laccoliths, dikes, and sills. (b) Igneous dikes cut across one another in this
outcrop. We can use cross-cutting relationships like this to date rocks (see Chapter 5).
58 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 58 07/11/16 5:28 pm

4. ultramafic rocks of the mantle give rise to mafic intrusive igne-
ous rocks called gabbros (Figure 3.4). Gabbros are very dark
in color because they contain relatively large amounts of iron
and magnesium. Gabbros are probably common at the base of
continental crust, and the boundary between ultramafic and
gabbroic rocks is typically interpreted as the base of the oce-
anic crust. Diabase is a more medium-grained mafic igneous
rock that is often found in dikes and sills.
Most continental crust is composed of granite, or rocks
of “granitic” composition (Figure 3.4). The term “granitic”
means the continental crust has an overall chemical com-
position similar, but not necessarily identical, to granite.
Granites consist predominantly of the minerals potassium
feldspar and silica-rich minerals such as quartz, and paper-
like micas; hence, granitic rocks are sometimes referred to
Courtesy of Fred Wehner, www.tug44.org.
as being felsic.
Between gabbro and granite are igneous rocks of inter-
FIGURE 3.3 The Palisades Sill along the Hudson River, north of mediate chemical composition. Like granite, these rocks also
New York City. These rocks are enriched in the mineral olivine and
tend to be associated with continental crust. One of the most
were intruded during the early rifting of the supercontinent Pangaea
important of these rocks is diorite. Unlike granite, diorite
(see the section “Tectonic Cycle” in Chapter 2).
does not have visible quartz crystals (Figure 3.4). Its white
and dark grains tend to impart a salt-and-pepper appearance
Intrusive igneous rocks also vary according to their chem- to it. Although diorite is sometimes involved in mountain
ical (mineralogic) composition. Rocks that are highly enriched building or other tectonic activity, granite is more commonly
in magnesium and iron, such as those within the mantle, are intruded as large felsic bodies. So, too, are granodiorites,
referred to as ultramafic. Rocks of the mantle are thought which are grayish rocks with a composition intermediate
to consist mainly of peridotite. At shallower depths in the between diorite and granite (Figure 3.4). Granodiorites, in
mantle, where lower pressures and temperatures are found, part, form the enormous batholiths of the Sierra Nevada of
(a) © Tyler Boyes/Shutterstock, Inc. (b) © Tom Grundy/Shutterstock, Inc.
(c) Courtesy of NASA/JPL. (d) Courtesy of NASA/JPL.
FIGURE 3.4 Types of phaneritic or coarse-grained igneous rocks. These kinds of igneous rocks are emplaced deep within the Earth’s crust,
allowing them to cool slowly and develop their coarse-grained crystalline texture. (a) Gabbro. (b) Granite. (c) Diorite. (d) Granodiorite.
3.2 Rock Cycle 59
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 59 07/11/16 5:28 pm

5. gabbro each have an extrusive counterpart that is their
chemical equivalent: rhyolite, andesite, and basalt, respec-
tively (Figure 3.6). Rhyolites, andesite, and basalt can
all occur on land, although basalts are more likely to erupt
onto the seafloor. For this reason ocean crust is commonly
referred to as being basaltic in composition. The texture of
all three types of extrusive rocks is said to be fine-grained,
or aphanitic (“without visible appearance”); aphanitic tex-
tures result from relatively rapid cooling and solidification
on Earth’s surface, leaving insufficient time for visible crystal
faces to grow (Figure 3.6).
Extrusive igneous rocks form in association with volca-
Courtesy of National Park Service. nic activity and can form distinctive features at Earth’s sur-
face indicative of their mode of origin. On land and in the
FIGURE 3.5 Yosemite Valley in the Sierra Nevada of California.
The Sierra Nevada consists of enormous batholiths of granodiorite sea, extrusive igneous rocks are represented by lava and lava
that were later exposed by uplift and erosion. The U-shaped flows (Figure 3.7). In the sea, lava flows produce distinctive,
Yosemite Valley seen here was carved out much later by glaciers. bulbous pillow lavas as the hot magma is rapidly quenched
by the much cooler seawater (Figure 3.7). Volcanoes can
also pump large amounts of volcanic ash and gaseous aerosols
California (Figure 3.5). These granodiorites were originally high into the atmosphere, blocking sunlight and cooling the
emplaced within the Earth and brought to the surface by Earth, but the climate change is normally temporary, last-
later uplift and erosion that formed the Sierra Nevada. ing only a few years (Figure 3.8). Eventually the ash rains
down, sometimes blanketing large areas. Ash deposits are
Extrusive igneous rocks: occurrence, instantaneous in terms of geologic time and if sufficiently
texture, and composition widespread are used to correlate, or “match,” deposits in
The magmas that form intrusive igneous rocks can also be widely separated areas (see Chapter 6). In the case of pumice,
extruded onto Earth’s surface. Thus, granite, diorite, and the rock is so filled with vesicles, it floats (Figure 3.6)!
(b) © Tyler Boyes/Shutterstock, Inc.
(a) © Tyler Boyes/Shutterstock, Inc.
(c) © Tyler Boyes/Shutterstock, Inc. Courtesy of Willie Scott/USGS.
(d)
FIGURE 3.6 Types of aphanitic or fine-grained igneous rocks. These kinds of igneous rocks are extruded at or near the Earth’s surface,
allowing them to cool rapidly so that visible crystals do not have time to form. (a) Basalt. (b) Andesite. (c) Rhyolite. (d) Pumice.
60 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 60 07/11/16 5:28 pm

6. © AbleStock. Courtesy of NOAA/OAR/National Undersea Research Program (NURP).
(a) (b)
FIGURE 3.7 Extrusive igneous rocks. (a) A lava flow on land. (b) Modern pillow lavas form during submarine volcanic eruptions.
If the volcanic vents or pipes that brought the magma magmas is less so. Granitic magmas have a greater concentra-
to the surface fill with solidified magma, the resulting volca- tion of silica than basaltic ones; thus as they near the surface
nic necks and dikes can form distinctive features at Earth’s and cool, they become less mobile. Consequently, granitic
surface after erosion of the surrounding rock (Figure 3.9). magmas are more likely to form large intrusions. If a vol-
Some magmas might also reach the surface through cracks cano does spew magma of granitic composition, the magma
or fissures in Earth’s crust as relatively gentle fissure eruptions. will tend to block the release of gases (like carbon dioxide
Volcanic eruptions sometimes produce terrains that can be and water vapor) until they come near the surface. When it
quite colorful, such as those of Yellowstone National Park reaches the surface, the gas rapidly expands (because of the
(refer to this chapter’s frontispiece). As we will see in coming lowered pressure), producing explosive eruptions.
chapters, enormous volcanic (including fissure) eruptions
are thought to have been important agents of catastrophic How do different kinds of magmas form?
climate change and mass extinction in Earth’s ancient past. The differing mineralogy and texture of igneous rocks leads
These fissure eruptions are thought to have injected enor- to a fundamental question: how does granite, or at least crust
mous volumes of carbon dioxide into the atmosphere, rap- with a granitic chemical composition, form? For that matter,
idly altering Earth’s surface temperature.
The styles of volcanic eruption—relatively gentle or
explosive—differ because of the viscosity of the magma.
Viscosity refers to the ability of a fluid to flow; molasses,
for example, is much more viscous than water. The most
important factor in determining viscosity is silica content;
the greater the silica content, the more viscous the magma
and the slower the flow. As a result, outpourings of basalt are
common at Earth’s surface, whereas the eruption of granitic
Courtesy of Ronald Martin, University of Delaware. © Tom Bean/Alamy Stock Photo.
FIGURE 3.8 Volcanic ash layer at hammer approximately 400 FIGURE 3.9 Shiprock, New Mexico, a volcanic vent exposed by
million years old exposed in northern Pennsylvania. erosion. The ridge is a feeder dike leading to the vent.
3.2 Rock Cycle 61
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 61 07/11/16 5:29 pm

7. given that many magmas are thought to originate in the the mantle. Mantle rocks such as peridotites are normally
mantle, which is ultramafic to mafic in composition, how do under enormous temperatures and pressures from the over-
magmas with andesitic or felsic compositions form? lying rocks, but the high pressure normally keeps them from
Several processes are involved and are referred to collec- melting. However, as mantle rocks move beneath mid-ocean
tively as magmatic differentiation. One of the most impor- ridges by upward convection, the pressure is released and
tant is called fractional crystallization (Figure 3.10). melting begins. Minerals with lower melting points, like
For example, as basaltic magma ascends toward Earth’s sur- those in basalt, melt first, separate, and rise from the remain-
face, it moves into zones of lower pressure and tempera- ing magma, producing basalt.
ture. As the magma rises, the minerals in the magma with Andesitic and more felsic magmas also likely form by
the highest melting points begin to crystallize and settle to other processes. Magma may assimilate (incorporate) more
the bottom, because as the magma temperature falls, those felsic rock—if present—through which it is rising, altering
minerals with the highest melting points reach their crys- the chemical composition of the magma. Magma mix-
tallization temperature first. Thus, minerals with the lowest ing might also occur when one body of magma overtakes
melting points are those that crystallize last from a magma. another as it rises toward the surface and mixes with it.
The minerals crystallize out in a definite sequence that More felsic magmas that generate granites are probably
has been demonstrated in laboratory experiments (called too enriched in silica to have been derived directly from mafic
Bowen’s Reaction Series after N. L. Bowen, who determined magmas. Rather, granitic magmas are probably generated by
the sequence). As iron-, magnesium-, and calcium-rich min- the differentiation of andesitic magmas or the partial melting
erals crystallize from magma and settle toward the bottom of of silica-rich continental rocks adjacent to the magma. The
the magma body, the magma left behind becomes progres- heat to melt the rocks likely comes from magma that has risen
sively enriched in sodium-plagioclase and then potassium through the rocks after being generated by plate subduction.
feldspar, micas, and leftover silica. Thus, the magma left The composition of extrusive igneous rocks—rhyolite,
behind becomes more felsic in composition and has a higher andesite, and basalt—also varies according to where volcanism
amount of silica and water than the original basaltic source. occurs. We can use this feature to infer past tectonic activity
Many magmas are thought to form through the process and the types of plate margins. Ocean crust, for example, is
of partial melting. Partial melting occurs because of the composed of basalt, so volcanic eruptions associated with
different melting points of minerals and changing temper- mid-ocean ridges are typically basaltic in composition. How-
atures within the lithosphere. Ultramafic rocks consist pre- ever, most of the 600 or so modern volcanoes occur where
dominantly of minerals with high melting points that are one lithospheric plate descends beneath another. If subduc-
relatively low in silica, whereas more felsic rocks consist of tion of ocean crust occurs beneath the margin of another piece
minerals that melt at lower temperatures and have higher of ocean crust, magmas of either basaltic or andesitic (more
silica contents (Figure 3.10). Ultramafic rocks dominate in silica-rich) composition are often produced. These magmas
Texture
Bowen’s Reaction Series (origin)
Discontinuous Continuous Phaneritic Aphanitic
Temperature series series (plutonic) (volcanic)
1200°
Olivine
Calcium
feldspar Gabbro Basalt
Pyroxene
(augite)
Amphibole Sodium Diorite Andesite
(hornblende) feldspar
Mica
(biotite)
Mica Potassium Granite Rhyolite
(muscovite) feldspar
700°
Quartz
Data from: http://comp.uark.edu/~sboss/study2s08.htm and http://www.skidmore.edu/~jthomas/fairlysimpleexercises/brs.html.
FIGURE 3.10 Bowen’s Reaction Series shows the fractional crystallization of minerals and the resulting igneous rocks. The pattern of
crystallization is Y-shaped. The branch called the continuous series represents the continuing enrichment of magma in sodium (Na) as
calcium (Ca)-rich rocks crystallize out.
62 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 62 07/11/16 5:29 pm

8. feed volcanic island arcs like the Aleutian Islands off Alaska. from the accumulation of shells of dead organisms. Thus,
Because the volcanoes are fed by less viscous basalt, the volca- sedimentary rocks frequently contain fossils, which are the
noes tend to occur at lower elevations and have a shield-like remains (shell, bone) or traces (tracks, trails) of preexisting
appearance because the lava flows more easily. organisms. Sedimentary rocks and their preserved fossils
On the other hand, if subduction occurs beneath a con- represent an enormous archive of past interactions of Earth’s
tinental margin, the remelting of crustal rocks and water- systems because they are indicative of surface conditions
laden sediments tends to produce magmas of andesitic such as sea level and related climatic feedbacks. For these
composition. These types of volcanoes include the Cascade reasons, we will postpone discussion of sedimentary rocks
Range of the Pacific Northwest and the Andes of South to Chapter 4, where we can more fully discuss their features
America (“andesite” derives from the fact that it is common and contained fossils.
in the Andes). If the magmas associated with plate subduc-
tion become sufficiently granitic in composition, rhyolites 3.2.3 Metamorphic rocks
result. However, rhyolites are not as common as andesites
because granitic magmas are less likely to be erupted; the All types of rocks can be subjected to changing tempera-
magma that feeds volcanic chains on land is more silica-rich, tures and pressures that physically and chemically transform
so that the magmas are more viscous and flow less easily. the rocks from one type to another. These processes are
Thus, volcanoes on land tend to build to higher elevations, referred to as metamorphism (“meta,” change; “morphos,”
giving them a steep, cone-like appearance. form). Unlike igneous rocks, metamorphism might involve,
By contrast to volcanism along plate margins, intra- at most, only partial remelting and rearrangement of grains
plate volcanism occurs within a plate. Examples include the in the rock. Metamorphism is frequently associated with
Hawaiian islands. These islands also appear to be associated the intense pressures and temperatures generated during
with a hotspot, where magma has reached the surface as if mountain building, but metamorphism also occurs in or
it had flowed through a pipe (see Chapter 2 for further dis- adjacent to subduction zones (where intense pressures and
cussion of the existence and behavior of hotspots). The types temperatures are also generated), in the solid rocks adjacent
of extrusive rocks produced by intraplate volcanism vary to magma, during the burial of rocks, or by the injection of
from basalts to rhyolites. The magmas erupting in Hawaii hot fluids into rocks.
are basaltic in composition, indicating they originate from
the mantle or the base of the lithosphere. The low silica con- Metamorphic rocks: texture and mineralogy
tent of the basaltic magmas lowers their viscosity, making During metamorphism, new textures and minerals form that
them flow more easily, accounting for the gentler slopes and are indicative of the intensity of the temperatures, pressures,
shield-like appearances of these volcanoes. and chemical conditions that occurred. Metamorphism
occurs in a variety of settings: the localized alteration of
CONCEPT AND REASONING CHECKS rock adjacent to hot magma; the production of hot fluids
by magma that are injected into the surrounding rock; or
much broader, or regional, metamorphism associated with
1. Draw a table indicating the major types of intrusive the generation of high temperatures and pressures during
igneous rocks and their extrusive counterparts.
mountain building
2. What processes cause magmas to change composition?
The intensity, or grade, of metamorphism is reflected by
the texture and mineralogy of the resulting rock. Let’s con-
3.2.2 Sedimentary rocks sider texture first. A basic distinction between different types
of metamorphic rocks is whether they are foliated or non-
A large proportion of Earth’s surface is covered by sedimen- foliated. Metamorphic rocks that exhibit a preferred orien-
tary rocks, which form at Earth’s surface. Sedimentary rocks tation of their mineral grains are said to be foliated (“folium,”
are typically layered, or stratified. Rocks that are uplifted leaf); foliation occurs in response to the increased pressure
and exposed to the atmosphere slowly undergo physical and other stresses of mountain building. Metamorphic rocks
and chemical weathering. Physical weathering transforms not exhibiting an orientation of mineral grains are said to be
larger rocks into smaller grains, whereas chemical weather- nonfoliated.
ing attacks chemical bonds within minerals, breaking them The lowest grade of metamorphism in foliated metamor-
down further. Physical and chemical weathering produce phic rocks occurs in slates, which form from fine-grained,
materials that are more easily removed and transported by clay-rich sedimentary rocks called shales at relatively low
the processes of erosion, which occurs by the action of land- temperatures and pressures (Figure 3.11). Slightly increased
slides, streams and rivers, wind, and glaciers. The eroded temperatures and pressures cause the tiny clay minerals in
grains are eventually deposited as loose sediment, which can shales to react chemically. This in turn causes the minerals to
eventually undergo lithification (consolidation or harden- reorganize and produce parallel arrangements of small mica
ing) during the processes of burial, compaction, and cemen- flakes that cause the slate to break along preferred planes,
tation to form a sedimentary rock (Figure 3.1). or slaty cleavage. A phyllite forms from shale under condi-
Not all sedimentary rocks form by erosion and depo- tions of higher temperature and pressure; phyllite is distin-
sition, however. Some form by chemical precipitation or guished from slate by its shinier appearance, which is caused
3.2 Rock Cycle 63
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 63 07/11/16 5:29 pm

9. (b) © Tyler Boyes/Shutterstock, Inc.
(a) © Tyler Boyes/Shutterstock, Inc.
(c) © Tyler Boyes/Shutterstock, Inc. (d) Courtesy of William S. Schenck, Delaware Geological Survey.
FIGURE 3.11 Foliated metamorphic rocks and the rocks from which they form. Different types of foliated sedimentary rocks form under
progressively more extreme conditions. (a) Slate forms under the least extreme conditions, when the platy clay minerals of a shale are
compressed together and realigned. (b) In schists, which may develop from shales and sandstones, mica crystals grow in size to give the
rock a scaly appearance. The small, red-colored dots are garnets, which recrystallize from the original minerals during metamorphism.
(c) In gneisses, which can form from a variety of sedimentary and igneous rocks, including granites, higher-grade metamorphism causes
the minerals to segregate into distinct bands. (d) Migmatites have a wavy, banded appearance and form by partial melting.
by slightly larger grain sizes and the presence of the micas Thus, the light-colored minerals with the lower melting
muscovite and chlorite. points tend to segregate from the darker-colored minerals
Under somewhat higher temperatures and pressures, that have not melted, imparting a distinct “wavy” banding
minerals such as micas grow to produce larger crystals visi- to migmatites.
ble to the naked eye, giving the rock a scaly appearance. This Another type of foliated metamorphic rocks form under
kind of foliation is called schistosity and the rocks are called somewhat different conditions than those above. Blueschist
schists. There are a variety of schists, but most are mica forms in the thick sedimentary wedges associated with
schists consisting of muscovite and biotite (Figure 3.11). subduction zones, where relatively high pressures but low
The mineral garnet, which only forms by metamorphism, temperatures occur. In subduction zones, the ocean crust
can also form from the minerals present in the original rock. initially begins to cool as it descends, so that relatively little
Even more intense metamorphism causes the miner- heat rises to the base of the rocks and sediments found in the
als in the original rock to recrystallize into distinct bands subduction zone. By contrast, the pressures due to compres-
to produce gneisses (Figure 3.11). Gneisses can form from sion and burial increase dramatically.
different rocks, including shales and alternating shales, Nonfoliated metamorphic rocks typically form from
sandstones, and even granite. Gneisses typically consist of parent rocks that consisted of essentially one mineral. Mar-
light bands of quartz, feldspars, and muscovite alternating ble is a nonfoliated metamorphic rock that forms during
with darker bands of amphiboles and biotite. Garnet is often the recrystallization and interlocking of the individual cal-
found in gneisses, as well (Figure 3.11). cite grains of limestones. Similarly, quartzites form by the
Even more intense alteration produces migmatites. recrystallization of individual quartz grains in sandstones.
Migmatites (meaning “mixed igneous and metamorphic”) Minor impurities in the original rocks can impart distinctive
form when partial—but not complete—melting occurs, pro- coloration to marbles and quartzites.
ducing a wavy, layered appearance (Figure 3.11). The wavy The intensity of metamorphism is also indicated by the
appearance results from the fact that light-colored silicate predominant minerals that compose the rocks. Chlorite is a
minerals like quartz and feldspar melt before more mafic greenish mica that is associated with greenschist, whereas
minerals with higher melting points such as hornblende. sillimanite is associated with the highest metamorphic grade
64 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 64 07/11/16 5:29 pm

10. (not coincidentally, sillimanite is used to make tempera- occur closest to the center of mountain belts, with gneisses,
ture-resistant porcelains like those used in spark plugs). Var- schists, phyllites, and slates tending to occur progressively
ious types of garnets characterize the different metamorphic farther away (Figure 3.12). The mineralogic composition of
grades between greenschist and sillimanite-bearing meta- the rocks parallels the gradation in foliation, with schist and
morphic rocks. gneiss occurring in the highest grade metamorphism and
slate and phyllite occurring in the lower grades. Blueschist is
Types of metamorphism associated with the high pressures that occur in the sedimen-
Most metamorphic rocks are generated by regional meta- tary wedges of subduction zones. However, in most cases,
morphism (Figure 3.12). As the term implies, regional meta- the patterns of metamorphism are more complex because of
morphism occurs over broad—or regional—scales, such as movement and deformation of the rocks during mountain
that associated with increased temperature and pressure and building and erosion thereafter (see Chapter 2).
large-scale deformation during orogeny, or mountain build- Another type of metamorphism important to the history
ing. We can use the intensity, or grade, of metamorphic rocks of Earth’s systems is hydrothermal metamorphism, or
associated with regional metamorphism to infer the intensity hydrothermal weathering, that occurs at seafloor spread-
of metamorphism, even after the mountains have long van- ing centers. Here, seawater percolates through hot ocean
ished. In the simplest, ideal case of regional metamorphism crust, altering the concentrations of certain dissolved ions in
the metamorphic grades are expressed as successive zones of the seawater (Figure 3.13). Changes in the concentrations of
decreasing metamorphism away from the centers of moun- these dissolved ions are recorded in the calcareous shells
tain belts where the deformation is greatest and magma is of fossil organisms and are used to infer past changes in rates
most likely to have been emplaced. Thus, migmatites tend to of seafloor spreading and continental weathering.
Deformed rocks
in mountain range
Undisturbed
sedimentary rocks
Shale Slate Phyllite Schist Gneiss
Igneous
Limestone Marble intrusion
Sandstone Quartzite
Chlorite
Muscovite (mica)
Biotite (mica)
Garnet
Staurolite
Sillimanite
200°C Metamorphism 800°C
FIGURE 3.12 Changes in lithology and mineralogy that result during the metamorphism. Certain minerals are indicative of metamorphism
and certain associations of these minerals are indicative of the intensity of metamorphism.
3.2 Rock Cycle 65
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 65 07/11/16 5:29 pm

11. West East
Seawater
enters rock Normal Red Sea seawater
Mid-ocean Seawater
Sharp change in salinity ridge enters rock
Brine pool
Metal
sulfides
Basalt
Groundwater Groundwater
Leaching of metals Leaching of metals
Hot magma
Data from: Bäcker, H. 1973. Rezente hydrothermal-sedimentäre Lagerstättenbildung. Erzmetall, 26, 544–555.
FIGURE 3.13 Hydrothermal weathering occurs when seawater percolates through hot ocean crust at seafloor spreading centers, such as
this one in the Red Sea. This mechanism alters the ionic composition of seawater. Magnesium (Mg2+) ions from ocean crust dissolve into
seawater as calcium (Ca2+) ions move from seawater into the crust. The ratio of Mg2+/Ca2+ ions appears to be related to the mineralogy of
the shells (calcite or aragonite) secreted by organisms living in the oceans.
Finally, there is impact or shock metamorphism, from destruction, but without the atmosphere life as we
which occurs when an extraterrestrial body such as an aster- know it on Earth would not exist. The atmosphere helps
oid hits the Earth (Figure 3.14). When an impact occurs, warm the Earth through the greenhouse effect (otherwise,
there is a tremendous and instantaneous increase in pressure life would freeze) and also protects Earth’s surface from
and temperature to thousands of degrees. Projectiles consist- harmful cosmic radiation.
ing of melted rock called tektites can be ejected thousands The lowest layer of the atmosphere, called the tropo-
of kilometers away from the site of impact (Figure 3.14). sphere, is about 10 to 15 kilometers in thickness. Although
Shocked mineral assemblages also form from impact. the troposphere is quite thin, it is where about 80% of the
Shocked minerals such as quartz have well-developed thin gases and almost all water vapor are concentrated. As a result,
layers, or laminae, that represent rearrangements of the crys- it is the troposphere where most of our “weather” occurs. The
talline structure of the mineral (Figure 3.14). The only way top of the troposphere, for example, is marked by the anvil
known to generate such well-developed laminae is by the shapes of storm clouds. The composition of the modern atmo-
impact of an extraterrestrial object. sphere is dominated by several gases. Nitrogen (78%) and
oxygen (21%) are by far the two most prominent components
(Figure 3.15). Although carbon dioxide comprises only
CONCEPT AND REASONING CHECKS 0.038% of the atmosphere by volume, this relatively small
amount of carbon dioxide is sufficient to warm Earth. Water
1. Diagram the sequence of metamorphic grades (phyllite, vapor is also present and contributes substantially to warming.
schist, gneiss, etc.) that one might encounter moving away Atmospheric circulation is driven, fundamentally, by the
from a batholith. temperature contrast between the equator and the poles and
2. What are the different types of metamorphism? results in turn from different fluxes of solar radiation reach-
3. Diagram the basic rock cycle on a subducting plate margin. ing the Earth’s surface. The atmosphere constantly attempts
to “smooth out” this temperature gradient by transferring
heat from the equator toward the poles by convection.
3.3Atmosphere and Its Let’s look at a simplified model of atmospheric circula-
tion (Figure 3.16). The sun’s rays penetrate a thinner layer
Circulation of atmosphere at the equator than at the poles because the
rays penetrate the atmosphere at more-or-less right angles
The atmosphere comprises the gaseous envelope sur- nearest the equator but more tangentially nearer the poles.
C rounding Earth. On the scale of the Earth, the atmo- Consequently, the sun’s rays entering the atmosphere over
sphere is only a thin veil that separates life on the planet the equator are less likely to collide with air molecules and
66 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 66 07/11/16 5:29 pm

12. Courtesy of Billy P. Glass, University of Delaware.
(a) Reproduced from: Christian Koeberl, “El’gygytgyn: a very special meteorite impact crater,” Website of the FWF (Austrian Science (b)
Fund), project: P21821-N19 (http://lithosphere.univie.ac.at/impactresearch/elgygytgyn-crater/). Accessed April 19, 2011.
Courtesy of Billy P. Glass, University of Delaware.
(c)
FIGURE 3.14 Impact metamorphism and its evidence. (a) Impact or shock metamorphism occurs when an extraterrestrial body such as
an asteroid hits the Earth. When an extraterrestrial object hits the Earth, there is a tremendous and instantaneous increase in pressure and
temperature to thousands of degrees. (b) Projectiles consisting of melted rock called tektites can be ejected thousands of kilometers.
(c) Shocked quartz. The parallel laminations represent the rearrangement of the mineral’s crystalline structure in response to sudden
intense pressure and temperature generated by an impact. Well-developed shocked mineral assemblages are much better indicators of
impact than iridium alone (see Chapter 1).
be scattered back to outer space than the rays that penetrate
the atmosphere nearer the poles. The more intense heating
at the equator causes the air to warm and rise there; because
it is warm, the air can also hold more moisture. As the warm
Argon 1%
Oxygen 21% air rises it loses heat energy and cools, releasing its moisture
Water vapor 0.3% as rain. It is for this reason rain forests occur in the tropics
Carbon dioxide 0.038%
near the equator. As the air masses rise into the atmosphere,
Ozone 0.01%
Methane 0.08% they begin to cool, so their density increases. Unlike the sim-
Nitrogen 78% Nitrous oxide 0.3% ple diagram in Figure 3.16a, however, the air masses stop
rising and the air begins to spread parallel to Earth’s surface
toward either pole (Figure 3.16b and Figure 3.17). This air
cools further as it flows parallel to Earth’s surface. These air
masses eventually cool sufficiently to further increase their
Data from: Mackenzie, F. T., and Mackenzie, J. A. 1995. Our Changing Planet: An Introduction to Earth System Science and Global Environmental density, causing them to descend back toward Earth before
Change. Englewood Cliffs, NJ: Prentice-Hall.
reaching the poles. Because these descending (high pres-
FIGURE 3.15 The composition of the modern Earth’s atmosphere. sure) air masses have already lost their moisture, the land
3.3 Atmosphere and Its Circulation 67
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 67 07/11/16 5:29 pm

13. Polar
high pressure
90°
Polar easterlies
Low 60°
Subpolar lows
Westerlies
High-pressure
North zone High 30°
ls
Pole Subtropical highs
ce l
i nd
v i ew o f w
Trades
Low Equatorial lows 0
c t i o n al
e
Equator
Low-pressure zone Trades
s- se os
Cr
High 30°
Subtropical highs
Westerlies
South High-pressure
Pole zone Subpolar lows
Low 60°
SIMPLE AIR CIRCULATION ON A Polar easterlies
NONROTATING EARTH 90°
Polar
(a) (b) high pressure
FIGURE 3.16 The structure and basic circulation of the atmosphere. (a) Cross-section of the Earth’s atmosphere showing the basic
components of highly simplified convection within the atmosphere as initially described in the text. Low-pressure zones are regions of
ascending moist air and rainfall, whereas high-pressure zones consist of descending dry air masses. (b) Differences in heating between the
equator and poles actually cause the formation of multiple convection cells in the atmosphere that determine the broad patterns of rainfall
and dryness, as further discussed in the text.
Polar Easterlies
Westerlies
Northeast Trades
Southeast Trades
Polar Easterlies
Data from: National Weather Service. JetStream: Online School for Weather (http://www.srh.noaa.gov/jetstream/global/circ.htm). Accessed March 31, 2010.
FIGURE 3.17 Major wind systems of the Earth resulting from atmospheric convection and the Coriolis effect. The curvature of the airflow
imparted by the Coriolis effect establishes the major wind patterns. As air descends at 30°E north and south latitude, it tends to move
from east to west over the Earth’s surface to produce the trade winds. Trade winds in the northern hemisphere flow from the northeast to
southwest, whereas their counterparts in the southern hemisphere flow from southeast to northwest; northern and southern hemisphere
trade winds meet at the Intertropical Convergence Zone above the equator. Warm air rising at about 60°E north and south latitude tends to
flow from west to east (again because of the Coriolis effect) to produce the westerlies (“coming from the west”) that move major weather
systems over the United States and Europe. The polar easterlies (“coming from the east”) lie toward the poles and move from east to west like
the trade winds, meeting the warmer westerlies along a polar front.
68 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 68 07/11/16 5:29 pm

14. beneath them often consists of deserts, such as the Sahara (discussed later in this Chapter) and the presence or
Desert in northern Africa. absence of mountain ranges (Box 3.1).
After its descent, the air flows parallel to the Earth’s sur-
face. Some air flows back toward the equator to be incorpo-
rated into the rising air there, whereas the rest flows toward CONCEPT AND REASONING CHECKS
higher latitudes. As it does so, the dry air picks up moisture
and warms once again, eventually rising into another con- 1. What drives atmospheric circulation?
vection cell. This pattern is repeated yet again in a third set 2. Diagram the circulation of the atmosphere, indicating the
of convection cells closest to the poles. major wind belts.
The flow of air within the convection cells is not sim- 3. Why does it rain so heavily in the tropics?
ply straight up and down; it is actually curved. The curva- 4. Diagram the orographic effect, indicating the processes
ture results from the Coriolis effect, which in turn results involved.
from the rotation of the Earth. The curvature of the airflow
imparted by the Coriolis effect establishes the major wind
patterns in Earth’s atmosphere (Figures 3.16 and 3.17).
The Coriolis effect exists because the atmosphere and the
3.4 The Hydrosphere
Earth move together as the Earth rotates eastward around its The hydrosphere is critical to maintaining Earth’s cli-
axis. As the Earth rotates, a point near the north pole moves D mate and life. The presence of water in sediments low-
around a circle that is much smaller in diameter than a point ers the melting point of rocks in subduction zones and is
at the equator. In other words, during the same interval of therefore critical to maintaining the processes of plate tec-
time, the point near the north pole travels a shorter distance tonics. Water also provides habitat for countless numbers of
than the point at the equator. Thus, the point near the north organisms and is necessary for life as we know it; most
pole moves more slowly than the point at the equator. Now organisms consist of more than 60% water, and some more
imagine that an air molecule at the north pole is displaced than 90%. Water is also critical to life because water vapor
toward the equator. Because of the physical phenomenon of is—like carbon dioxide—a greenhouse gas, affecting Earth’s
inertia (which states that an object continues to move with temperature and habitability.
the same speed and direction unless a force acts upon it), the
air molecule maintains the original speed and direction that 3.4.1 Hydrologic cycle
it had when it began to move south toward the equator. Con-
sequently, the molecule moving from the north pole toward Like other Earth systems, the hydrosphere is cyclic. The
the equator will lag behind the one at the equator because hydrologic cycle involves the flux of water through several
the point at the equator is moving faster than the point com- reservoirs (Figure 3.18). Precipitation reaches the ground
ing from the north pole; thus, the point at the equator will as rain or snow if the air just above the land is sufficiently
have moved eastward away from where the point from the cold, such as at high latitudes near the poles or at high eleva-
north pole will arrive. Conversely, a point moving from the tions (mountains). Some precipitation may undergo evapo-
equator toward the north pole will move ahead of the point ration or flow over Earth’s surface as runoff in streams and
at the pole. A similar phenomenon occurs in the southern rivers; as is described in Chapter 2, the occurrence of some
hemisphere, but the movements are the reverse, or mirror of the major river systems of the world is determined by the
image, of those in the northern hemisphere. presence of deep valleys within the Earth’s crust that rep-
Because of the Coriolis effect, as air descends within resent failed rift systems. Much of this water will of course
the atmospheric convection cells at 30° north and south reach the oceans, whereas some infiltrates the ground and
latitudes, the air masses tend to move from east to west flows through subterranean rocks and sediments as ground-
over Earth’s surface to produce the trade winds. Trade water. The remaining water in the cycle is used by plants,
winds in the northern hemisphere flow from the north- which are technically part of the biosphere (Figure 3.19).
east to southwest, whereas their counterparts in the south- Most land plants lose tremendous amounts of water out the
ern hemisphere flow from southeast to northwest. Trade bottom of the leaves through the process of transpiration.
winds in the northern and southern hemispheres con- The water is lost through countless numbers of microscopic
verge near the equator. Similar phenomena account for the openings called stomata that allow the exchange of carbon
well-known westerlies (coming from the west) that move dioxide and oxygen between the leaves and the environment
major weather systems over the United States and Europe during photosynthesis. The process of transpiration is tre-
and the polar easterlies (which come from the northeast mendously important to the hydrologic cycle, because with-
in the northern hemisphere and the southeast in the south- out transpiration many tropical regions would suffer from
ern hemisphere) nearer the poles. As we will see below, drought.
the basic pattern of atmospheric circulation determines not Some workers recognize a separate Earth system
only the broad pattern of precipitation over the planet but referred to as the cryosphere, that includes glaciers, both
also the broad distribution of Earth’s biotas while driving those of mountains (called alpine glaciers) and polar ice
the major surface currents of the ocean. These patterns are caps. The development of polar glaciers depends on the sup-
in turn influenced by the distribution of the continents ply of moisture that is part of the overall hydrologic cycle.
3.4 The Hydrosphere 69
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 69 07/11/16 5:29 pm

15. Box 3.1 Asian Monsoon: Influence of Large Land Masses on Atmospheric
Circulation and the Hydrologic Cycle
Large land masses can profoundly influence geologic time? How, in other words, did the Asian
the circulation of the atmosphere through the monsoon evolve toward its present state? How can we
phenomenon of monsoons. The word “monsoon” is tell what happened? One way to determine the effects
usually associated with torrential rainfall but actually of the Himalayan Orogeny on Asian climate, especially
refers to reversing airflow (Box Figure 3.1A). given the complex interactions of Earth’s systems, is
Approximately 50 to 60 million years ago, the to use computer models of climate change. A model
continent of India began to collide with the continent is a kind of sophisticated hypothesis (see Chapter 1)
of Asia, resulting in the Himalayan Orogeny and that tries to take into account all the components
leading to the Asian monsoon over Tibet and India. or processes of a system that are important to the
What we see today is that, as the summer sun warms system while excluding those that are not considered
the Tibetan Plateau to the north of India, warm air important. Using climate models, we can run
begins to rise, drawing warm moist air from the experiments on complex systems under controlled
Indian Ocean over India. When this warm, moist air conditions, like running experiments in a laboratory.
encounters the south side of the Himalayas, which This allows earth scientists to identify the mechanisms
form a narrow rampart along the southern margin that cause variation in global climate because many
of the Tibetan Plateau, the air is forced upward by factors can be held constant, whereas others are varied
the orographic effect. As the air rises it cools, and to examine their effect on the behavior of the model.
precipitation results on the southern side of the Based on climate models, as India collided with
Himalayas, leaving Tibet high and dry. During the Asia the fluctuations in the climate of the Tibetan
winter the reverse conditions hold: cold air, which is Plateau became more extreme because land was
dense, descends over Tibet and southward over India. being uplifted higher into the atmosphere. Because
This airflow is also considered part of the monsoon. of the increasing elevation of the plateau, the
But what exactly were the effects of the Himalayan atmosphere over the plateau became progressively
Orogeny on climate and the Asian monsoon through thinner. As a result, the sun warmed the air near
Precipitation
Rain shadow on
Wind leeward side
BOX FIGURE 3.1A A monsoon like that of the Indian subcontinent.
70 Chapter 3 Earth Systems: Processes and Interactions
© Jones & Bartlett Learning, LLC, an Ascend Learning Company. NOT FOR SALE OR DISTRIBUTION
9781284457162_CH03_056_084.indd 70 07/11/16 5:29 pm

Book a Trial Class

Download