Question

Our earth 9th class ssc key points

Answer 1

• The earth is made up of several concentric layers with one inside another.
• Crust – The uppermost layer over the earth’s surface.
• It is the thinnest of all the layers.
• It is about 35 km. on the continental masses and only 5 km. on the ocean floors.
• The main mineral constituents of the continental mass are silica and alumina. It is thus called si-al (si-silica and al-alumina)
• The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)
• Mantle – Just beneath the crust is the mantle which extends up to a depth of 2900 km.
• Core – The innermost layer is the core with a radius of about 3500 km.
• It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous, i.e. iron).
• The central core has a very high temperature and pressure.