QCM : Earth's Interior and Surface Contrasts — 10 questions

Questions et réponses du QCM

1. What does the bimodal altitude distribution of Earth's surface represent?

The uniform elevation of all Earth's landmasses.
The gradual variation in Earth's surface elevation from poles to equator.
The random distribution of mountain ranges and basins across the planet.
The presence of two distinct altitude peaks corresponding to oceanic and continental domains.

The presence of two distinct altitude peaks corresponding to oceanic and continental domains.

Explication

The bimodal altitude distribution refers to the two distinct peaks in Earth's relief, with one representing oceanic domains (deep trenches) and the other representing continental domains (high mountains). This reflects the contrasting properties and compositions of oceanic and continental crusts, making option two the correct choice.

2. What are the main rocks that compose the oceanic crust?

Quartzite and schist
Basalt and gabbro
Granite and sedimentary rocks
Sandstone and limestone

Basalt and gabbro

Explication

The oceanic crust is mainly composed of basalt and gabbro, which are mafic, low in silica, and formed from magma cooling at mid-ocean ridges. These rocks are explicitly mentioned as the primary constituents of oceanic crust in the content, making option two the correct answer.

3. What is the primary role of continental crust rocks like granite in Earth's geology?

They act as the primary reservoir for Earth's water.
They are mainly responsible for Earth's magnetic field.
They form the stable, heterogeneous layer that shapes Earth's surface and supports landforms.
They serve as the main source of fossil fuels.

They form the stable, heterogeneous layer that shapes Earth's surface and supports landforms.

Explication

Continental crust rocks like granite form the Earth's surface layer, providing stability, support for landforms, and influencing geological processes, which is their primary role in Earth's geology.

4. When was the Mohorovicic discontinuity (Moho) first identified?

1981
1936
1914
1909

1909

Explication

The Mohorovicic discontinuity was first identified by Andrija Mohorovičić in 1909, marking the boundary between Earth's crust and mantle based on seismic wave velocity changes.

5. How do the composition and physical properties of continental and oceanic crusts differ?

Continental crust is mainly basalt and gabbro, mafic, denser, and thinner than oceanic crust.
Continental crust is primarily sedimentary rocks, while oceanic crust is mainly metamorphic, with no significant difference in density.
Continental crust is mainly granite, silica-rich, less dense, and thicker than oceanic crust.
Both crusts have similar composition but differ in thickness and seismic velocity.

Continental crust is mainly granite, silica-rich, less dense, and thicker than oceanic crust.

Explication

The continental crust is mainly composed of granite, a silica-rich, felsic igneous rock, with a lower density (~2.7) and greater thickness (30-65 km), whereas oceanic crust is mainly basalt and gabbro, mafic rocks with higher density (~2.9) and thinner (5-15 km). This contrast reflects their different mineralogical and chemical compositions, which influence their physical properties.

6. Who is credited with discovering the seismic boundary that separates Earth's crust from the mantle?

André Mercier
Andrija Mohorovičić
Richard Dixon Oldham
Inge Lehmann

Andrija Mohorovičić

Explication

Andrija Mohorovičić is credited with discovering the Moho discontinuity in 1909, which is the seismic boundary separating Earth's crust from the mantle. The other options are notable geoscientists but did not identify this specific boundary.

7. What causes the seismic discontinuities such as the Moho and Gutenberg boundaries within Earth?

Changes in temperature at different depths
Variations in seismic wave velocities due to earthquake activity
Tectonic plate movements causing fractures
Differences in material composition and physical state

Differences in material composition and physical state

Explication

Seismic discontinuities like the Moho and Gutenberg are caused by abrupt changes in Earth's material composition and physical state, which result in significant increases or decreases in seismic wave velocities at these boundaries.

8. How are thermal structure models like PREM used in practice to understand Earth's internal heat transfer processes?

They use magnetic field data to estimate the thermal conductivity of Earth's layers.
They analyze surface heat flow measurements to model deep Earth temperatures.
They interpret seismic velocity data to infer temperature and layer boundaries within Earth.
They directly measure temperature at various depths using seismic waves.

They interpret seismic velocity data to infer temperature and layer boundaries within Earth.

Explication

Thermal structure models like PREM interpret seismic velocity data and discontinuities to infer temperature distributions and layer boundaries inside Earth, providing insights into heat transfer processes. They do not directly measure temperature or rely solely on surface heat flow or magnetic data, but instead analyze seismic wave behavior to model Earth's internal thermal state.

9. Which key feature best distinguishes heat transfer by conduction from heat transfer by convection within Earth's interior?

Conduction is more efficient in the Earth's mantle due to high temperatures, while convection is dominant in the crust due to its rigidity.
Conduction is characterized by large-scale fluid circulation, while convection is limited to microscopic particle interactions.
Conduction occurs via molecular vibrations within solids, with heat transfer driven by temperature gradients, whereas convection involves the bulk movement of fluid or semi-fluid material, driven by buoyancy.
Conduction involves heat transfer through fluid movement, while convection occurs through molecular vibrations in solids.

Conduction occurs via molecular vibrations within solids, with heat transfer driven by temperature gradients, whereas convection involves the bulk movement of fluid or semi-fluid material, driven by buoyancy.

Explication

The correct feature is that conduction involves heat transfer through molecular vibrations within solids driven by temperature gradients, whereas convection involves the bulk movement of fluid or semi-fluid material, such as in the mantle. This fundamental difference in mechanisms is the key distinguishing characteristic.

10. What are thermal anomalies within Earth's interior?

Modes of heat transfer such as conduction or convection
Seismic discontinuities like Moho or Gutenberg
Global average temperature increase due to climate change
Localized deviations in temperature detected through seismic tomography

Localized deviations in temperature detected through seismic tomography

Explication

Thermal anomalies are localized deviations in temperature within Earth's interior, identified through variations in seismic wave velocities, and are associated with features like mantle plumes or subduction zones.

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Bimodal Altitude Distribution — definition?

Two distinct peaks: oceanic (-4500 m) and continental (+300 m).

Crust composition — continental rocks?

Primarily granite, silica-rich, coarse-grained, ~2.7 density.

Crust composition — oceanic rocks?

Mainly basalt and gabbro, mafic, denser (~2.9), fine- to coarse-grained.

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