Correct Answer: Option B) 2 & 3
The Earth's crust is the outermost solid layer of our planet, and understanding its characteristics is fundamental to geography and geology
Statement 1: Its thickness is uniform throughout - false
The Earth's crust does not have uniform thickness. It varies significantly across different regions:
Continental crust averages 30-50 km thick but can extend up to 70 km under mountain ranges
Oceanic crust is much thinner, averaging only 5-10 km thick
The thickness varies based on geological processes, age, and location
Statement 2: It is thickest under mountain ranges - True
This statement is correct. Mountain ranges represent areas where the continental crust is thickest due to:
Tectonic collision processes that compress and thicken the crust
Isostatic adjustment where thicker crust "floats" higher on the mantle
Examples include the Himalayas, Andes, and Rocky Mountains where crustal thickness can reach 60-70 km
Statement 3: The average density of oceanic crust is greater than continental crust - True
This is accurate because:
Oceanic crust is primarily composed of basalt and gabbro (density ~3.0 g/cm³)
Continental crust is mainly composed of granite and sedimentary rocks (density ~2.7 g/cm³)
The higher density of oceanic crust is due to its mafic composition rich in iron and magnesium
