Chapter 13: Earth Materials and Plate Tectonics

Define and distinguish a. continental crust and oceanic crust, and b. the lithosphere and asthenosphere.

-Oceanic crust-basaltic, denser, and thinner than continental crust-granitic. Oceanic crust- underlies the ocean basins while continental crust dominates Earth's land areas that rise above sea level -lithosphere- solid outer part of Earth (including oceanic crust, continental crust, and the uppermost mantle down to the asthenosphere). The lithosphere is RIGID and BRITTLE and is not as deformable as the underlying PLASTIC asthenosphere (next layer down within the upper mantle). Asthenosphere- solid but flows plastically because of its temperature (heat currents) and pressure characteristics

How do minerals differ from rocks? Provide examples of each.

-mineral- solid, naturally occurring inorganic substance with a crystalline form and specific chemical composition where rocks are naturally formed aggregates of minerals -Examples of minerals: Halite (table salt), quartz, and diamonds -Examples of rocks: igneous, sedimentary, and metamorphic rocks -Igneous rocks: solidified directly from a molten (melted) state, either above or below Earth's surface (examples: basalt, granite) -Sedimentary rocks: Sedimentary—accumulations of rock fragments or other deposits turned into hard rock by compaction and/or cementation (examples: sandstone, limestone) -Metamorphic rocks: preexisting rock changed into a different rock type by heat and pressure (examples: marble, schist)

Name the major zones of Earth's interior from the center to the surface. How do these zones differ from one another?

-the inner core, outer core, mantle, oceanic crust, continental crust -vary in composition, thickness, and density (which decreases outward from Earth's center). All zones are solid, except the outer core (liquid). The mantle-thickest layer, and oceanic crust- thinnest

Define paleogeography. Why are geographers interested in this topic?

-the study of ancient physical geography—the distributions and patterns of physical features and fossil life forms in ancient, prehistoric times -Understanding the past helps geographers (and other scientists) understand how our planet became as it is today, and how it may change in the future

Describe the three major categories of rock and the principal means by which each is formed. Give an example of each.

Based on their mineralogy, chemical composition, and texture, rocks can be classified into three categories. They are sedimentary rocks, igneous rocks, and metamorphic rocks. Sedimentary rocks are formed when minerals and organic particles are transported by water and consolidated into a single mass in the soil of a broad floodplain. The Igneous rocks are formed from cooled and solidified magma. Two kinds of igneous rocks, intrusive and extrusive, are distinguished by their mineralogy and silica content. Metamorphic rocks are formed from the sedimentary or igneous rocks that are changed by intense temperature or pressure. Sometimes these changes may take millions of years. Sandstone is an example of sedimentary rocks. Basalt is an igneous rock. Marble is a metamorphic rock.

Why does Earth have layers?

Early in Earth's history, denser elements such as iron and nickel settled to the center while less-dense elements migrated to the surface.

lithospheric plate

Earth's exterior is broken into several of these large regions (plates) of rigid and brittle crust and upper mantle (lithosphere).

How do we know the deep structure (the layering) of Earth?

Earthquakes and the seismic waves they release can be used to infer layering.

Which of the following time intervals represents the longest span of geologic time?

Eons

Explain why the eastern portion of the United States has relatively little tectonic activity compared with the western portion of the United States.

Geologists believe that when a main continent collides with numerous segments of crust, the continent begins to grow in size by accumulating chunks of crust through a process called accretion. The North American plate is moving westward. As it moved, it collided with numerous chunks of crust and they all added to the main continent over the past 200 million years. So, the main continent grew in this manner. The small chunks or segments of crust that are added to the main continent are called microplate terranes. These terranes have their own distinct geologic characteristics. On the east side, no such accumulation took place. So, the western portion of the United States has relatively more tectonic activity compared with the eastern portion of the United States.

How does the formation of the Hawaiian Islands support plate tectonic theory?

Hawaiian Islands formed individually when each was situated over a stationary HOTSPOT. They show plate tectonic movement to the northwest because the islands get progressively older and less active volcanically in that direction

Which is Earth's most common rock type?

Igneous rock

What is the rock cycle?

Over long periods of time, a given rock-forming mineral can become part of different kinds of rocks—igneous, sedimentary, and metamorphic. Rock matter can solidify, weather, lithify, metamorphose through heat, pressure, and melt. The rock cycle represents how rock-forming minerals move from one rock type to another

In which eon did multicellular life, such as animals and plants, begin to appear?

Phanerozoic

crust:

Relatively thin, approximately 8-64 kilometers (5-40 mi) deep, low-density surface layer of Earth.The crust is the only portion of the lithosphere of which Earth scientists have direct knowledge, yet it represents only about 1% of Earth's planetary mass

How does rock metamorphism occur?

Rock is buried and subjected to intense heat and pressure deep within the Earth for long periods of time.

How do the lithosphere and asthenosphere differ?

The lithosphere is an elastic solid, while the asthenosphere is a plastic solid.

What is geologic time?

The period of time extending from the formation of the Earth to the present

How is the concept of uniformitarianism related to plate tectonics theory and the arrangement of the continents today?

Uniformitarianism states that the processes that we observe today are the same ones that occurred in the geologic past. The geologic processes that we observe today may not have operated at the same rate everywhere on Earth. The spatial variability of Earth's landform features is the result of changing intensities of these processes. The theory of plate tectonics is compatible with the concept of uniformitarianism which can explain various phenomena, including continental drift, earthquakes and volcanic eruptions, formation of mountain ranges, and seafloor spreading. Although many of Earth's surface features appear to be unchanging, they are changing at a very slow pace over thousands or millions of years.

Compare and contrast the theory of continental drift and the theory of plate tectonics.

Unlike Wegener's theory of continental drift, plate tectonics includes a plausible mechanism—convection in the mantle- for lithospheric plate movement

What evidence did Wegener rely on in the formulation of his theory of continental drift? What evidence did he lack?

Wegner used the geographic distributions of fossils, rock types, and rock ages, as well as the fit of continental coastlines as evidence of his theory of continental drift. He lacked a plausible mechanism for moving huge continental masses on Earth's surface. Plate tectonics has provided the mechanism, which consists of lithospheric plates moving along with the plastic flowing asthenosphere. The asthenosphere flows plastically due to heat currents in the mantle

island arc

a chain of volcanic islands along a deep oceanic trench; found near tectonic plate boundaries where subduction is occurring.

outcrop

a mass of bedrock exposed at Earth's surface that is not concealed by regolith or soil.

hot spot

a mass of hot molten rock material at a fixed location beneath a lithospheric plate.

rock cycle

a representation of the processes and pathways by which Earth material becomes different types of rocks.

elastic solid

a solid that withstands stress with little deformation until a maximum value is reached, whereupon it breaks.

rock

a solid, natural aggregate of one or more minerals or particles of other rocks.

polarity reversal

a time in geologic history when the south magnetic pole became the north magnetic pole and vice versa.

What type of lithospheric plate boundary is found a. paralleling the Andes, b. at the San Andreas Fault, c. in Iceland, and d. near the Himalayas?

a. Andes: continental-oceanic convergence b. San Andreas: transform, with lateral movement c. Iceland: oceanic-oceanic divergence d. Himalayas: continental collision and suturing

unconformity

an interruption in the accumulation of different rock layers; often represents a period of erosion.

plastic solid

any solid material that changes its shape under stress, and retains that deformed shape after the stress is relieved.

bedding plane

boundary between different sedimentary layers.

Which line of evidence did Alfred Wegener use to support the continental drift hypothesis?

continental fit and fossil distributions

Which term best describes the action of two plates moving towards each other?

convergence

stratification

distinct layers within sedimentary rocks, called strata.

The history of human existence spans millennia, which by most accounts is a very long time! However, the presence of humans on our planet represents a miniscule unit of time when considering the overall age of the Earth. The geologic time scale is a valuable tool used by earth scientists to understand Earth's history, rock units, mass extinctions, and how life

evolved.

core:

extremely hot and dense innermost portion of Earth's interior composed primarily of iron and nickel

core

extremely hot and dense innermost portion of Earth's interior; the molten outer core is 2400 kilometers (1500 mi) thick; the solid inner core is 1120 kilometers (700 mi) thick.

tectonic force

force originating within Earth that breaks and deforms Earth's crust.

What is the basis for classifying rocks as igneous, sedimentary, or metamorphic?

formation

What does the term "seafloor spreading" refer to?

formation of new crust at mid-ocean ridges

joint

fracture or crack in rock.

When basalt containing very small iron particles cools into rock, these iron particles ______.

give the rock a magnetic signature aligned with Earth's magnetic field at the time they cooled

transform movement

horizontal sliding of tectonic plates alongside and past each other.

Which type of rocks can become metamorphic rocks?

igneous, sedimentary, and metamorphic

seismograph

instrument used to measure amplitude of passing seismic waves.

Bruhnes, a French geologist, discovered that ______.

iron particles in some basaltic rock did not align with Earth's current magnetic field

midoceanic ridge

linear seismic mountain range that interconnects through the major oceans; it is where new molten crustal material rises through the oceanic crust.

Contrast the lithosphere with the asthenosphere.

lithosphere- asthenosphere--rigid outer shell - partially molten layer -uppermost part of the layer -Earth's upper mantle

What is Earth's largest layer by mass and volume?

mantle

According to the rock cycle, what type(s) of rock(s) can a sedimentary rock become?

metamorphic only

mantle

moderately dense, relatively thick (2885 km/1800 mi) middle layer of Earth's interior that separates the crust from the outer core.

lava

molten (melted) rock matter erupted onto Earth's surface; solidifies into extrusive igneous (volcanic) rocks.

magma

molten (melted) rock matter located beneath Earth's surface from which intrusive igneous rocks are formed.

plate divergence

movement of lithospheric plates away from each other.

plate convergence

movement of lithospheric plates toward each other and colliding.

seafloor spreading

movement of oceanic crust in opposite directions away from the midoceanic ridges, associated with the formation of new crust at the ridges and subduction of old crust at ocean margins.

mineral:

naturally occurring inorganic substance with a specific chemical composition and crystalline structure.

Which properties must a mineral have?

naturally occurring, inorganic, crystalline solid

catastrophism

once-popular theory that Earth's landscapes developed in a relatively short time by cataclysmic events.

metamorphic rock

one of the three major categories of rock; formed by heat and pressure changing a pre-existing rock.

igneous rock

one of the three major categories of rock; formed from the cooling and solidification of molten rock matter.

sedimentary rock

one of three major rock categories; formed by compaction and cementation of rock fragments, organic remains, or chemical precipitates.

Which branch of study relies on geologic and climatological evidence to reconstruct historical and geographical environments of Earth's features?

paleogeography

pyroclastics (tephra)

pieces of volcanic rock, including cinders and ash, solidified from molten material erupted into the air.

Which theory states that convection cells in the mantle cause the movement of lithospheric pieces on the asthenosphere?

plate tectonics

subduction

process associated with plate tectonic theory whereby an oceanic crustal plate is forced downward into the mantle beneath a lighter continental plate when the two converge.

crust

relatively thin, approximately 8-64 kilometers (5-40 mi) deep, low-density surface layer of Earth.

lithosphere (planetary structure)

rigid and brittle outer layer of Earth consisting of the crust and uppermost mantle.

organic sedimentary rock

rock created from deposits of organic material, such as carbon from plants (coal).

chemical precipitate sedimentary rock

rock created from dissolved minerals that have precipitated out of water.

clastic sedimentary rock

rock formed by the compaction and cementation of preexisting rock debris.

extrusive igneous rock

rock solidified at Earth's surface from lava; also called volcanic rock.

intrusive igneous rock

rock that solidified within Earth from magma; also called plutonic rock.

Which type of rock forms from deposition, compaction, and sedimentation?

sedimentary

What is the primary method scientists have used to learn about the interior structure and composition of Earth?

seismic waves

clast

solid broken piece of rock, bone, or shell.

bedrock

solid rock of Earth's crust that underlies soil and other unconsolidated materials.

paleogeography

study of the past geographical distribution of environments.

continental shield

the ancient part of a continent that consists of crystalline rock.

The rock cycle describes ______.

the change of one rock type to another through the processes of erosion, transportation, compaction, cementation, melting, and metamorphism

continental collision

the fusing together of landmasses as tectonic plates converge.

paleomagnetism

the historic record of changes in Earth's magnetic field.

continental crust

the less dense (average mass of 2.7 g/cm^3), thicker portion of Earth's crust; underlies the continents.

foliation

the occurrence of banding or platy structure in metamorphic rocks.

inner core:

the solid, innermost portion of Earth's core, probably of iron and nickel, that forms the center of Earth

inner core

the solid, innermost portion of Earth's core, probably of iron and nickel, that forms the center of Earth.

oceanic crust

the thinner and denser (averaging 3.0 g/m^3), basaltic portion of Earth's crust; underlies the ocean basins.

outer core:

the upper portion of Earth's core; considered to be composed of molten iron liquefied by Earth's internal heat

mantle:

the upper portion of Earth's core; considered to be composed of molten iron liquefied by Earth's internal heat consists of silicate rocks (high in silicon and oxygen) that also contain significant amounts of iron and magnesium

outer core

the upper portion of Earth's core; considered to be composed of molten iron liquefied by Earth's internal heat.

continental drift

theory proposed by Alfred Wegener stating that the continents joined, broke apart, and moved on Earth's surface; it was later replaced by the theory of plate tectonics.

plate tectonics

theory that superseded continental drift and is based on the idea that the lithosphere is composed of a number of segments or plates that move independently of one another, at varying speeds, over Earth's surface.

asthenosphere

thick, plastic layer within Earth's mantle that flows in response to convection, instigating plate tectonic motion.

cross bedding

thin layers within sedimentary rocks that were deposited at an angle to the dominant rock layering.

Compared to continental crust, oceanic crust is _____.

thinner and denser

seismic wave

traveling wave of energy released during an earthquake or other shock.

What is the idea that Earth processes operated historically in much the same ways as they act today?

uniformitarianism

uniformitarianism

widely accepted theory that Earth's geological processes operate today as they have in the past.

Mohorovičić discontinuity (Moho)

zone marking the transition between Earth's crust and the denser mantle.