Geology Exam 1

Which of the choices below is a diagnostic characteristic of a mineral?

Minerals only occur as solids

Which region in the Earth is considered to liquid?

Outer Core

Why does P-wave velocity decrease dramatically at the core-mantle boundary?

P-wave velocity decreases at the core-mantle boundary because the outer core is liquid.

Describe the important differences between P-waves and S-waves

P-waves can pass through a liquid and travel approximately twice as fast as S-waves (which cannot pass through a liquid).

Which ion would you expect to find in the sulfate mineral class?

SO42-

A scientist identifies a rock sample as peridotite. Why did she do so?

She observed that the rock was low in silica, making it ultramafic.

The ________ are the mineral class that accounts for more than 90 percent of the Earth's crust.

Silicates

At a ________, an oceanic plate will be forced beneath another plate because of differences in density.

Subduction Zone

Why do both P-waves and S-waves gradually bend as they move through the mantle?

The mantle gets increasingly dense and strong with depth because of the increasing pressure. This difference affects both P-wave and S-wave velocities, and they are refracted toward the lower density mantle material (meaning they are bent out toward Earth's surface).

What is luster?

The quality of light reflected from a mineral's surface

What aspect of plate tectonics was not included in the Hess theory?

The trenches associated with subductions zones are the deepest parts of the oceans.

What is the lithosphere composed of?

The upper mantle

What process leads to convection in the mantle?

Transfer of heat from the core to the mantle leads to heating of lower mantle rock. When heated, the rock expands and its density is reduced. Because the mantle is plastic, this lower-density material tends to rise toward the surface, and cooler denser mantle material moves in to take its place.

A/an _________ is a long, narrow trough in the seafloor formed where a portion of an oceanic plate sinks into the mantle.

Trench

What parts of Earth are most closely represented by typical stony meteorites and typical iron meteorites?

Typical stony meteorites are similar in composition to the Earth's mantle, while typical iron meteorites are similar to the core.

What role does water play in generating magma?

Water lowers the melting temperature of the rock, allowing it to melt.

A shale is:

a clastic (detrital) sedimentary rock composed of mud-sized sediment

Which of the following magma compositions will produce the most explosive volcanic eruptions?

a gas-rich, felsic magma

Galena is an example of:

a sulfide mineral

A(n) ________ is a type of unconformity with parallel beds of sedimentary rock above and metamorphic or igneous rocks below the erosional surface.

disconformity

The mineral quartz is an example of:

framework silicate mineral

The mineral olivine is an example of a(n):

isolated silicate

What are the six common nonsilicate mineral groups?

oxides, native elements, carbonates, halides, sulfides, sulfates

Every plate boundary can be recognized by:

the presence of active volcanoes

A geologist observing a break in a rock formation consisting of sedimentary layers concludes that the layers were displaced as a result of fault movement. Which principle is described here?

the principle of cross-cutting relationships

A geologist observes that fragments of a granite are incorporated into the sandstone that sits on top of the granite and concludes that the granite is older than the sandstone. Which principle is described here?

the principle of inclusions

A magnitude 5 earthquake has _____ times more shaking than an magnitude 4 earthquake.

10

Order the given layers of the Earth in the correct order. A. First Layer (Surface) B. Second Layer C. Third Layer D. Fourth Layer E. Fifth Layer

A. Crust B. Upper Mantle C. Lower Mantle D. Outer Core E. Inner Core

Which statement best summarizes the greenhouse effect?

After absorbing solar energy, Earth's surface emits long-wave radiation, which is absorbed by water vapor, carbon dioxide, and other trace gases in the atmosphere. These gases in turn emit some of the energy back down to Earth.

Earth's lithosphere is located:

Between the lower mantle and outer core

What property distinguishes the earth's crust, mantle, and core?

Composition

What is the likely relationship between mantle plumes and the development of a continental rift?

Continental crust is lighter than oceanic crust and cannot sink low enough into the mantle to become an ocean (although this can happen over limited areas, and commonly does happen along coastal areas of continental plates).

One of the driving forces of plate motion is:

Convection currents in the mantle

The Mohorovicic discontinuity lies at the boundary of what two layers?

Crust and Mantle

How do light-colored igneous rocks differ from dark-colored rocks?

Dark-colored igneous rocks have a higher iron and magnesium content than light-colored rocks

What was the rate of cooling and the environment of formation for an extrusive igneous rock and why?

Fast because it was erupted from a volcano

________ is defined as a mineral's resistance to scratching.

Hardness

What are some of the processes that take place at a divergent plate boundary?

Hot mantle rock moving toward the surface partially melts because the pressure is reduced. The magma produced moves upward into cracks in the crust and is extruded onto the sea floor

The core is most likely composed of:

Iron

Dinosaurs first appear in the geological record in rocks from about 215 Ma and then became extinct 65 Ma. For what proportion (%) of geological time did dinosaurs exist?

. 215 - 65 = 150 Ma. Since the age of the Earth is 4570 Ma, this represents 150/4,570 = 0.033 or 3.3% of geological time.

Match the type of plate boundary with the appropriate description. 1. Convergent boundary 2. Divergent boundary 3. Transform boundary

1. Two plates move toward each other 2. Two plates pull apart from each other. 3. Two plates slide past each other.

The following choices contain densities of various materials. Based on these data, which will yield the fastest seismic velocity?

5.6 g/cm3

In what way is a mineral different from a rock?

A mineral has a specific chemical composition and lattice structure. Rocks are made out of minerals, and most rocks contain several different types of minerals.

Which of the following is consistent with the plate tectonic theory?

As a plate subducts into the asthenosphere, it pulls the trailing plate along.

If a typical rate for the accumulation of sediments is 1 mm/year, what thickness (metres) of sedimentary rock could accumulate over a period of 30 million years?

At 1 mm/y 30,000,000 mm would accumulate over that 30 million years. This is equivalent to 30,000 m or 30 km. Few sequences of sedimentary rock are even close to that thickness because most sediments accumulate at much lower rates, more like 0.1 mm/y.

The minerals calcite (CaCO3) is an example of which type of mineral?

Carbonate

As you can see in Figure 9.19, British Columbia is still experiencing weak post-glacial isostatic uplift, especially in the interior, but also along the coast. Meanwhile offshore areas are experiencing weak isostatic subsidence. Why?

During the Pleistocene glaciation British Columbia was pushed down by glacial ice and mantle rock flowed slowly out beneath the ocean floor. Now that the land area is rebounding, that mantle rock is flowing back and the offshore areas are subsiding.

Where and how is Earth's magnetic field generated?

Earth's magnetic field is generated within the liquid outer part of the core by the motion of the metallic core material.

List three ways in which geologists can contribute to society

Geologists provide information to reduce the risk of harm from hazards such as earthquakes, volcanoes, and slope failures; they play a critical role in the discovery of important resources; they contribute to our understanding of life and its evolution through paleontological studies; and they play a leading role in the investigation of climate change, past and present and its implications.

In what way is geology different from the other sciences, such as chemistry and physics?

Geology involves integration of various different sciences (chemistry, physics, and biology for example), but also requires an understanding of the importance of billions of years of geological time.

Describe the lattice structure and elemental composition of the mineral halite.

Halite is composed of sodium (Na) and chlorine (Cl) with the Na+ and Cl- ions alternating with one another in all three directions within a cubic structure.

How would you expect the depth to the crust-mantle boundary in the area of the Rocky Mountains to differ from that in central Saskatchewan?

In the area of the Rocky Mountains the crust is thickened and pushed down into the mantle. In Saskatchewan the crust is thinner and does not extend as far into the mantle.

Why does subduction not take place at a continent-continent convergent zone?

In the late 19th century the trans-Atlantic paleontological matchups were explained by assuming that there must have been land bridges between the continents at some time in the past, or that terrestrial organisms had floated across the ocean on logs.

Describe the spatial and depth distribution of earthquakes at ocean ridges and ocean trenches.

It was (and still is) assumed that high heat flow exists where mantle convection cells are moving hot rock from the lower mantle toward the surface, and that low heat flow exists where there is downward movement of mantle rock.

How does mantle convection contribute to plate tectonics?

Mantle convection creates the traction that can force plates to move around on the surface.

Basalt is most likely to be found in the:

Oceanic Crust

Which of the following is not part of the definition of a mineral?

Organic

Which seismic wave(s) would be most useful in determining the extent and thickness of the Earth's interior layers?

P and S Wvaves

What is a mantle plume and what is its expected lifespan?

Paleomagnetic studies showed that old rocks on the continents had different pole positions than they do today, and also that they were progressively more different with time past. This implied either that the poles had moved or that the continents had moved. It was also found that the apparent polar wandering paths for different continents were different, and this supported the concept that the continents had moved.

How would some familiarity with biology be helpful to a geologist?

Paleontology is an important aspect of geology and requires an understanding of biology, including evolution, the physiology of animals and plants and ecological relationships

In the model for ocean basins developed by Harold Hess, what took place at oceanic ridges and what took place at oceanic trenches?

The ocean ridge areas are the youngest parts of the sea floor and thus there hasn't been time for much sediment to accumulate.

Every plate boundary can be recognized by:

The presence of an earthquake belt

What is likely to happen to western California over the next 50 million years?

The primary technical weakness of Wegener's theory was that he had no realistic mechanism for making continents move.

A glassy igneous texture indicates that:

The rock cooled very quickly not leaving time for crystals to form.

A single plate can carry both oceanic and continental crust. This statement is: True or False?

True

The mantle is one of Earth's chemical layers. This statement is:

True

How does decompression melting occur?

When hot, solid mantle rock descends, it moves to areas of lower pressure. This reduction in pressure allows the hot material to melt into a less compressed liquid phase.

What are plate boundaries at which lithospheric plates: a) move toward each other b) move past each other c) move away from each other called?

a) convergent b) transform c) divergent

The Aleutian and Japanese Islands are the result of plate motion along a:

ocean-to-ocean convergent plate boundary

Where are Earth's most recent sites of continental rifting and creation of new ocean floor?

(a) Contractionists assumed that mountains formed because as the Earth contracted the crust wrinkled into mountains. (b) Permanentists assumed that mountains formed by the geosynclinal process.

______ is a feature of a divergent plate boundary. CHOOSE ALL THAT APPLY

- A rift valley - An oceanic ride

________ is a feature that results from processes associated with an oceanic-oceanic convergent plate boundary. CHOOSE ALL THAT APPLY

- An ocean trench - A volcanic Arc

Which igneous texture has only visible crystals that are a few millimeters across?

Phaneritic

How is it possible for a plate to include both oceanic and continental crust?

Prior to 1920, ocean depths were measured by dropping a weighted line over the side of ship. Echo sounding techniques were developed at around that time and that greatly facilitated the measurement of ocean depths.

A ________ is a solid, naturally occurring, cohesive substance composed of minerals or mineral-like materials.

Rock

Describe the nature of movement at an ocean ridge transform fault (a) between the ridge segments, and (b) outside the ridge segments.

Temperature increases quite rapidly with depth in the crust, but much less so in the mantle, and this implies mantle convection.

What geological situation might eventually lead to the generation of a subduction zone at a passive ocean-continent boundary such as the eastern coast of North America?

The evidence used by Wegener to support his idea of moving continents included matching continental shapes and geological features on either side of the Atlantic; common terrestrial fossils in South America, Africa, Australia, and India; and data on the rate of separation between Greenland and Europe.

What property of the mantle is essential for the isostatic relationship between the crust and the mantle?

The isostatic relationship between the crust and the mantle is dependent on the plastic nature of the mantle

What is the evidence for mantle convection, and what is the mechanism that causes it?

The key evidence for mantle convection is that the rate of temperature increase within the mantle is less than expected and this can only be explained by a mantle that is mixing by convection. The mechanism for convection is the transfer of heat from the core to the mantle.

When were the last two reversals of Earth's magnetic field?

The last two reversals of Earth's magnetic field were at the beginning of the present Brunhes normal chron (0.78 Ma), and at the end of the Jaramillo normal subchron (0.90 Ma).

What is the main component of Earth's core?

The main component of Earth's core is iron (Fe).