Question

earth’s core is probably

1. composed of mostly iron and nickel.
2. hollow.
3. composed of rock with high silica content.
4. molten throughout.
5. composed of potassium and aluminium - rich silicates.

009 3.0 points
which of the following statements about the asthenosphere is not true?

1. it behaves plastically.
2. it is a rigid rock layer.
3. it has the same composition as the lower mantle.
4. it lies beneath the lithosphere.
5. it acts like a lubricating layer allowing plates to move.

010 3.0 points
the ocean crust is composed mostly of

1. peridotite.
2. rind.
3. basalt.
4. granite.
5. gabbro.

012 3.0 points
the thickness of earth’s crust varies because of
i) variations in composition.
ii) variations in density.
iii) variations in temperature.

1. i & ii only
2. ii only
3. iii only
4. i only
5. i, ii, & iii

013 3.0 points
one of the most general conclusions to be drawn from plate tectonic theory is that

1. earth’s geography has continually changed.
2. the ocean basins are continually enlarging.
3. earth is slowly shrinking.
4. earth is continually losing heat.
5. earth is slowly expanding.

014 3.0 points

Explanation:

Question 009 (About asthenosphere)

The asthenosphere is part of the upper mantle, behaves plastically (so 1 is true), lies beneath the lithosphere (4 is true), acts as a lubricant for plate movement (5 is true), and has the same composition as the lower mantle (3 is true). A rigid rock layer is the lithosphere, not the asthenosphere, so statement 2 is not true.

Oceanic crust is mainly composed of basalt (a type of mafic igneous rock). Peridotite is in the mantle, rind, basalt (wait, option 2 is "rind"? Wait, correct: ocean crust is mostly basalt? Wait, no, option 2 is "rind"? Wait, maybe typo, but standard: oceanic crust is made of basalt (or more accurately, gabbro in the lower part and basalt on top, but among options, "basalt" – wait, option 2 is "rind"? Wait, maybe the options have "basalt" as option 2? Wait, the user's image: options are 1. peridotite, 2. rind? No, maybe OCR error. Wait, standard answer: oceanic crust is composed mostly of basalt (or gabbro, but if option 2 is "basalt" (maybe typo as "rind"? No, maybe "basalt"). Wait, correct answer: ocean crust is mostly basalt, so if option 2 is basalt (maybe OCR error), but assuming, the ocean crust is composed mostly of basalt (option 2? Wait, no, peridotite is mantle, granite is continental crust. Wait, maybe the option is "basalt" (option 2). So the answer is 2.

Crust thickness varies due to composition (continental vs oceanic: different compositions) and density (continental crust is less dense, thicker; oceanic is denser, thinner). Temperature doesn't directly affect thickness. So I (variations in composition) and II (variations in density) are correct, III is not. So 1. I & II only.

Answer:

1. It is a rigid rock layer.

Question 010 (Ocean crust composition)