RICE

EARTH’S INTERIOR

About 

  • Geology: Scientific study of Earth’s composition, structure, rocks, soil, and processes. Father of Geology: James Hutton.  
  • Direct Data Sources: Volcanoes, rocks.  
  • Indirect Data Sources: Temperature, meteorites, earthquakes.  
  • Kola Superdeep Borehole (Russia): Deepest human drilling (~12 km). South African mines reach ~3–4 km.  

Crustal Element Composition 

  • Most Abundant Element: Oxygen (46.6%).  
  • Most Abundant Metal: Aluminium (8.1%).  
  • Other Elements: Silicon (27.7%), Iron (5.0%), Calcium (3.6%), Sodium (2.8%), Potassium (2.6%), Magnesium (2.1%), Others. 

Layers of the Earth 

Layer Composition Thickness Mean Density Key Characteristics 
Crust Silica & Aluminium (SiAl)  5–70 km  Continental: 2.7~g/cm^3  Oceanic: 2.9~g/cm^3 Overall brittle. Volume: 1% | Mass: 1%  
Mantle Silica & Magnesium (SiMa)  ~2,900 km  4.5~g/cm^3 Divided into Upper & Lower Mantle. Volume: 84%   Mass: 68%  
Core Nickel & Iron (NiFe)  Outer: ~2,200 km Inner: ~1,220 km  13~g/cm^3 Outer core is liquid (magnetic); Inner core is so 

Crust Sub-divisions 

  • Continental Crust: Thicker (30 km), lighter, granitic rock, landmasses.  
  • Oceanic Crust: Thinner (5 km), denser, basaltic rock, ocean floor.  

Lithosphere & Asthenosphere 

  • Lithosphere: Rigid outermost layer comprising the crust and uppermost solid mantle (10–200 km thick).  
  • Asthenosphere: Semi-solid/semi-molten layer (extends up to 400 km) beneath the lithosphere. It is mechanically weak, ductile, and serves as the primary source of magma. Not part of the Lithosphere.  

Discontinuities  

  • Conrad: Upper Crust & Lower Crust  
  • Mohorovicic (Moho): Lower Crust & Upper Mantle  
  • Repetti: Upper Mantle & Lower Mantle  
  • Gutenberg: Mantle & Core  
  • Lehmann: Outer Core & Inner Core  

PYQ (earth interior) 

  1. The Mohorovicic (Moho) discontinuity separates which two layers of the Earth? (RRB NTPC (Graduate 2024))

 (a) Upper Crust and Lower Crust  

 (b) Crust and Mantle 

 (c) Mantle and Core  

 (d) Outer Core and Inner Core 

Correct Answer: (b) Crust and Mantle 

  1. Which layer accounts for the largest proportion of the Earth’s total volume (approximately 84%)? (RRB NTPC (Graduate 2025))

 (a) Crust  

  (b) Mantle  

 (c) Outer Core  

 (d) Inner Core 

Correct Answer: (b) Mantle 

  1. What are the primary chemical constituents that make up the Earth’s continental crust? ( RRB ALP 2025)

 (a) Silica and Magnesium  

 (b) Silica and Aluminium  

 (c) Nickel and Iron|  

(d) Magnesium and Iron 

Correct Answer: (b) Silica and Aluminium (SIAL) 

  1. The ‘Asthenosphere’, which is the main source of magma during volcanic eruptions, is located in which part of the Earth? (RRB NTPC (UG 2024))

 (a) Lower Crust  

 (b) Upper Mantle  

 (c) Outer Core  

 (d) Inner Core 

Correct Answer: (b) Upper Mantle 

  1. What is the physical state of the Earth’s Outer Core? ( RRB NTPC (Graduate 2025))

(a) Solid  

(b) Liquid (molten)  

(c) Gaseous  

(d) Plasma 

Correct Answer: (b) Liquid (molten)