FAQs on Types of Rocks & Sea Floor Spreading Theory

Question 1

1. What's the difference between igneous, sedimentary, and metamorphic rocks for UPSC Geography?

Accepted Answer

Ans. Igneous rocks form from molten magma cooling either beneath Earth's surface (intrusive) or above it (extrusive). Sedimentary rocks develop from compressed sediment layers over time, often containing fossils. Metamorphic rocks result from existing rocks transforming under extreme heat and pressure without melting. Each type has distinct mineral composition, texture, and formation environments crucial for understanding crustal geology and plate tectonics.

Question 2

2. How does sea floor spreading prove that continents are moving apart?

Accepted Answer

Ans. Sea floor spreading occurs at mid-ocean ridges where new oceanic crust forms as magma rises and pushes existing plates sideways. Magnetic striping patterns on the ocean floor-symmetrical bands of reversed magnetism on either side of ridges-demonstrate consistent seafloor creation rates. This mechanism directly supports continental drift theory, showing Earth's lithosphere continuously renews and redistributes, causing continents to separate measurably over millions of years.

Question 3

3. Why do oceanic basaltic rocks differ from continental granitic rocks in composition?

Accepted Answer

Ans. Oceanic crust primarily consists of basalt, a dense mafic rock rich in iron and magnesium, formed from rapid cooling of lava at mid-ocean ridges. Continental crust contains granite, a light felsic rock abundant in silica and aluminium, crystallised slowly from magma underground. These compositional differences explain why oceanic lithosphere is denser and sinks beneath lighter continental plates during subduction, a key process in plate boundary interactions.

Question 4

4. What role do fossil records in sedimentary rocks play in dating geological time periods?

Accepted Answer

Ans. Fossils embedded in sedimentary rock layers act as biological markers for specific time periods, enabling relative dating through stratigraphic correlation. Different organisms dominated distinct geological eras-trilobites in the Paleozoic, dinosaurs in the Mesozoic-allowing scientists to identify rock age without absolute measurements. This fossil succession principle helps UPSC candidates understand how sedimentary sequences reveal Earth's evolutionary history and climate changes across geological timescales.

Question 5

5. Can metamorphic rocks tell us about ancient plate collisions and mountain formation?

Accepted Answer

Ans. Metamorphic rocks preserve evidence of extreme pressure and temperature conditions occurring during continental convergence and orogenesis. High-grade metamorphic minerals like garnet and sillimanite indicate deep crustal burial during mountain-building events. By studying metamorphic mineral assemblages and foliation patterns in rocks like schist and gneiss, geologists reconstruct ancient plate collision zones-critical for understanding the Himalayas' formation and similar orogens relevant to Indian geography studies.

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