Earth Structure — Set 1
Geography · पृथ्वी की संरचना · Questions 1–10 of 50
What is considered the primary source of internal heat for the Earth?
Correct Answer: C. Radioactive decay and primordial heat
The main sources of Earth's internal heat are the decay of radioactive isotopes and the residual heat from the planet's formation. This primordial heat has been trapped since the Earth coalesced. This heat drives geological processes like plate tectonics.
Which layer of the Earth lies immediately beneath the crust?
Correct Answer: B. Mantle
The Mantle lies immediately beneath the crust. It extends to a depth of approximately 2,900 kilometers. It is composed of silicate rocks that are richer in iron and magnesium than the crust.
The 'Asthenosphere' is best described as which of the following?
Correct Answer: B. A semi-fluid weak zone in the upper mantle
The Asthenosphere is a mechanically weak and ductile region of the upper mantle. It lies just below the lithosphere. Its semi-fluid nature allows tectonic plates to move over it.
The core of the Earth is primarily composed of which two elements?
Correct Answer: C. Nickel and Iron
The core is primarily composed of Nickel and Iron, often referred to as NIFE. It is the densest part of the Earth. Heavy metals sank to the center during the planetary differentiation process.
Which components together constitute the 'Lithosphere'?
Correct Answer: B. The Crust and the uppermost solid Mantle
The Lithosphere consists of the Crust and the uppermost rigid part of the Mantle. It behaves as a brittle, rigid solid. It is broken into tectonic plates that float on the asthenosphere.
Oceanic crust is primarily composed of which type of rock?
Correct Answer: D. Basalt
Oceanic crust is primarily composed of Basalt. Basalt is a dark, fine-grained igneous rock rich in iron and magnesium. It is denser and thinner than continental crust.
Continental crust is primarily composed of which type of rock?
Correct Answer: B. Granite
Continental crust is primarily composed of rocks similar to Granite. Granite is lighter in color and less dense than the basalt of the oceanic crust. This lower density allows continents to 'float' higher on the mantle.
The boundary separating the Earth's crust from the mantle is known as?
Correct Answer: B. Mohorovicic Discontinuity
The boundary between the crust and the mantle is the Mohorovicic Discontinuity, often called the Moho. It was discovered by observing a sharp increase in the velocity of seismic waves. Its depth varies significantly between oceans and continents.
Which type of seismic wave cannot travel through liquid?
Correct Answer: C. S-waves (Secondary waves)
S-waves (Secondary or Shear waves) cannot travel through liquids or gases. They are transverse waves that require a rigid medium to propagate. Their inability to pass through the outer core proves it is liquid.
Which seismic waves are the fastest and the first to arrive at a seismograph?
Correct Answer: C. P-waves (Primary waves)
P-waves (Primary waves) are the fastest seismic waves. They are compressional waves that can travel through solids, liquids, and gases. Because of their speed, they are the first signal recorded during an earthquake.