Daily Current Affairs Quiz: August 26, 2025

Answer: A [Both Statement 1 and Statement 2 are correct, and Statement 2 is the correct explanation of Statement 1.]
Explanation:

1. The Earth’s interior is structured into crust, mantle, outer core, and inner core.
2. The inner core, composed primarily of iron and nickel, is solid despite temperatures exceeding 5000–6000°C.
3. Under normal conditions, such temperatures would keep these metals in liquid state.
4. However, the immense pressure (estimated around 3.6 million atmospheres) at the Earth’s center counteracts the effect of high temperature, forcing the atoms into a solid crystalline structure.
5. This pressure-induced solidification explains why the inner core is solid while the outer core, subjected to slightly lesser pressure, remains molten.
6. The presence of a liquid outer core is critical, as it drives convection currents that generate Earth’s magnetic field.
7. Thus, both Statement 1 and Statement 2 are correct, and Statement 2 is the correct explanation of Statement 1.

Answer: B [2 only]
Explanation:

Statement 1 is incorrect: The Earth’s crust is the outermost layer, varying in thickness. Continental crust averages 30–70 km, while oceanic crust averages only 5–10 km. Hence, continental crust is thicker, not oceanic

Statement 2 is correct: The Mohorovičić discontinuity (Moho), discovered by Andrija Mohorovičić in 1909, is the boundary between the crust and mantle. Seismic waves were observed to suddenly increase in velocity below this layer, revealing a compositional difference, lighter silicate rocks in the crust versus denser ultramafic peridotite in the mantle.

Answer: C [1 and 2 only]
Explanation:

Statement 1 is correct: The lithosphere comprises the Earth’s crust and upper rigid mantle, extending up to ~100 km. Beneath it lies the asthenosphere (~100–250 km deep), a mechanically weak zone characterized by plastic and ductile flow. It is partly molten.

Statement 2 is correct: Asthenosphere has pockets of magma that enable lithospheric plates to move. This is the layer where isostatic adjustments and mantle convection currents occur, driving plate tectonics.

Statement 3 is incorrect: The asthenosphere is not completely rigid; its semi-molten nature allows for the movement of tectonic plates above it.

Answer: B [Convection currents in the outer core]
Explanation:

1. Earth’s magnetic field originates from the geodynamo mechanism in the liquid outer core. The outer core is primarily composed of molten iron and nickel, which are good conductors of electricity.
2. Convection currents generated by heat escaping from the inner core, combined with Earth’s rotation (Coriolis effect), create complex fluid motions.
3. These motions generate electric currents, which in turn produce a magnetic field.
4. The solid inner core does not generate the field but may stabilize it.
5. Mantle and crustal movements are unrelated to the generation of the geomagnetic field, though they can locally influence magnetic anomalies.

Answer: D [1, 2, 3, 4 and 5]
Explanation:

Seismology has identified several discontinuities inside the Earth, where abrupt changes in seismic wave velocity mark boundaries between different layers:

1. Repetti discontinuity: Separates the upper mantle and lower mantle (~700–1000 km depth). It explains the change in velocity and density in mantle materials.
2. Lehmann discontinuity: Discovered by Inge Lehmann in 1936, it marks the boundary between the liquid outer core and the solid inner core (~5100 km depth).
3. Conrad discontinuity: Occurs at ~15–20 km depth within the continental crust, separating the upper granitic crust from the lower basaltic crust.
4. Mohorovičić (Moho) discontinuity: Found at ~35 km depth under continents and ~7 km under oceans, it separates the crust from the mantle.
5. Gutenberg discontinuity: Lies at ~2900 km depth, marking the boundary between the mantle and the liquid outer core. Identified through the absence of S-waves beyond 103° from the epicenter.