Question

The depth of the earth's crust is ___ to ____ kms.

• A. 20 - 60
• B. 25 - 80
• C. 30 - 100
• D. 40 - 150

Answer 1

Answer: (C)

• The size of the Earth -- about 12,750 kilometers (km) in diameter-was known by the ancient Greeks, but it was not until the turn of the 20th century that scientists determined that our planet is made up of three main layers--Crust,Mantle and Core.
  
• This layered structure can be compared to that of a boiled egg. The Crust,the outermost layer, is rigid and very thin compared with the other two.
  
• Beneath the oceans, the crust varies little in thickness, generally extending only to about 5 km.
  
• The thickness of the crust beneath continents is much more variable but averages about 30 km; under large mountain ranges, such as the Alps or the Sierra Nevada, however, the base of the crust can be as deep as 100 km.