The Lithosphere:
The surface of the earth made up of solid rock and soil is called the lithosphere. It comprises the seven continents and the rocky ocean beds. Land, the part of the lithosphere that is not immersed under seas and oceans, occupies about 29 per cent of the total surface area of the earth. Continents are large land masses on the surface of the earth. They are usually separated from each other by water bodies called oceans. The edges of the continents extend up to the rocky ocean floors. Together the continents and the ocean floors form the lithosphere.
The Structure of the Earth:
The earth is divided into three main layers.
Crust:
The crust is solid. It has two parts, the upper layer is made up of SIAL (silica + aluminum) and the lower layer is made up of SIMA (silica + magnesium). The thickness of the crust varies from 8 to 50 km. It is thicker under the continents and thinner under the oceans. The mean density of this layer is around 2.7 and 3.
Mantle:
The mantle is semi-solid and rich in iron and magnesium. This layer is about 2,850 km wide and its average density is between 3.5 and 5.5.
Core:
The core has two parts, the outer core and the inner core. The outer core is liquid, while the inner core is solid. The core starts at about 2,900 km from the earth's surface and is rich in nickel and iron. The mean density of this layer varies from 5.1 to 13. The earth's crust is composed of mineral and rocks. Minerals are natural substances that have definite chemical compositions, and these minerals compacted together form rocks. Minerals are inorganic substances. The most common minerals found in the earth's crust are silica, quartz, feldspar, mica, calcite, dolomite, gypsum, etc. There are approximately 2,000 minerals in the earth's crust which combine together to form rocks.
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