CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
A sudden decrease in P-wave velocity occurs when waves enter the:
A. Upper crust
B. Liquid outer core
C. Solid inner core
D. Atmosphere
Correct Answer: B
P-waves slow sharply when passing from the solid mantle into the liquid outer core.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The sudden disappearance of S-waves at the core boundary was crucial evidence for a:
A. Liquid outer core
B. Hollow mantle
C. Solid atmosphere
D. Granite inner core
Correct Answer: A
S-wave absence beyond the core-mantle boundary demonstrated that the outer core is liquid.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which statement about Earth's outer core is correct?
A. It is solid and transmits S-waves
B. It is liquid and does not transmit S-waves
C. It is part of the lithosphere
D. It is composed mainly of granite
Correct Answer: B
The outer core is liquid, which is why shear S-waves cannot pass through it.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which statement about Earth's inner core is correct?
A. It is liquid because temperature is high
B. It is solid because immense pressure raises the melting point
C. It is made mainly of silicate crust
D. It is colder than the crust
Correct Answer: B
Despite very high temperature, pressure is sufficient to keep the iron-rich inner core solid.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The asthenosphere is not completely molten; instead it is mostly:
A. Solid but capable of slow ductile flow
B. Liquid water
C. Metallic gas
D. Vacuum
Correct Answer: A
The asthenosphere is predominantly solid rock that can deform and flow slowly under long-term stress.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The lithosphere is described as rigid because it:
A. Flows freely like a liquid
B. Behaves elastically/brittly on geologic timescales compared with the asthenosphere
C. Contains no rocks
D. Has zero pressure
Correct Answer: B
The lithosphere is mechanically strong and relatively rigid compared with the weak asthenosphere beneath it.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which of the following is a mechanical rather than compositional division?
A. Core
B. Mantle
C. Crust
D. Lithosphere
Correct Answer: D
Lithosphere is defined by mechanical behavior; crust, mantle and core are compositional divisions.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which of the following is NOT a major compositional layer of the Earth?
A. Crust
B. Mantle
C. Core
D. Asthenosphere
Correct Answer: D
The asthenosphere is a mechanical layer, not one of the three major compositional layers.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The Conrad discontinuity, where identifiable, lies within the:
A. Continental crust
B. Outer core
C. Inner core
D. Lower mantle
Correct Answer: A
The Conrad discontinuity has historically been used for a boundary between upper and lower continental crust and is not globally continuous.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which boundary lies at approximately 5,150 km depth?
A. Moho
B. Gutenberg discontinuity
C. Lehmann discontinuity
D. Conrad discontinuity
Correct Answer: C
The Lehmann discontinuity marks the outer-core/inner-core boundary near 5,150 km depth.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which boundary lies at approximately 2,900 km depth?
A. Moho
B. Gutenberg discontinuity
C. Lehmann discontinuity
D. 410-km discontinuity
Correct Answer: B
The Gutenberg discontinuity at about 2,900 km separates the mantle from the outer core.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The D'' layer is located:
A. Near Earth's surface
B. At the base of the mantle above the core
C. Inside the crust
D. At the center of the inner core
Correct Answer: B
D'' is a complex boundary region in the lowermost mantle just above the core-mantle boundary.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The mantle transition zone is important because it:
A. Separates atmosphere from crust
B. Contains major pressure-induced mineral transformations
C. Is entirely molten
D. Contains no seismic waves
Correct Answer: B
Major phase transitions of mantle minerals occur in the 410–660 km depth range.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The 410-km and 660-km boundaries in the mantle are mainly associated with:
A. Changes in atmospheric gases
B. Mineral phase changes under pressure
C. Ocean currents
D. Crustal erosion
Correct Answer: B
At these depths, mantle minerals transform into denser crystal structures because of high pressure.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Oceanic crust is generally:
A. Older than all continental crust
B. Younger than much continental crust
C. The same age everywhere
D. Unrelated to plate tectonics
Correct Answer: B
Oceanic crust is continually created and recycled, so it is generally much younger than the oldest continental crust.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
Which type of crust is generally denser?
A. Continental crust
B. Oceanic crust
C. They are exactly equal
D. Neither contains minerals
Correct Answer: B
Oceanic crust is mafic and denser, commonly around 3.0 g/cm³, compared with continental crust near 2.7 g/cm³.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
According to the Pratt model of isostasy, topographic differences are mainly due to variations in:
A. Crustal density
B. Core temperature
C. Earth's rotation rate
D. Ocean salinity
Correct Answer: A
The Pratt model explains elevation differences mainly by lateral density variations at a common compensation depth.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
According to the Airy model of isostasy, high mountains are supported by:
A. Deep crustal roots
B. Very dense upper crust
C. A thinner crust
D. A liquid outer core
Correct Answer: A
The Airy model assumes crust of similar density but varying thickness, with mountains having deep roots.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The concept of isostasy explains:
A. Why the atmosphere rotates
B. Gravitational balance of the lithosphere on denser underlying material
C. Formation of Earth's magnetic field
D. Origin of seismic waves
Correct Answer: B
Isostasy describes the gravitational equilibrium of crustal or lithospheric blocks on the denser mantle.
CSS - PMS - CCE - PCS - Geography
Earth's Shape and Structure
The high average density of Earth compared with surface rocks suggests:
A. A hollow interior
B. Dense material at depth
C. No metallic core
D. Only sedimentary rocks inside
Correct Answer: B
Earth's mean density is much higher than crustal rocks, indicating dense materials concentrated in the interior.