Geography, SS 1, Week 8
Topic: Earth’s Structure
Content:
- The Earth’s structure
- Importance of atmosphere
- Importance of hydrosphere
- The Internal structure of the Earth
Introduction – The Earth
Earth is unique among the known planets: it has an abundance of water. Other worlds — including a few moons — have atmospheres, ice, and even oceans, but only Earth has the right combination to sustain life.
Earth’s oceans cover about 70 percent of the planet’s surface with an average depth of 2.5 miles (4 kilometers). Fresh water exists in liquid form in lakes and rivers and as water vapor in the atmosphere, which causes much of Earth’s weather.
The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. The earth’s structure is divided into two groups namely Outer structure and Inner structure.
The outer (external) structure of the earth is made up of the following layers.
1. The Atmosphere: the atmosphere is made up of a mixture of gases which cover the earth. The Atmosphere contains 73% of Nitrogen, 1% of Oxygen, 0.03% of carbon and 0.97% inert gases.
Importance of the Atmosphere
(i) The atmosphere provides gases essential for respiration
(ii) The atmosphere provides Nitrogen for plants
(iii) The atmosphere contain ozone layer which is the shield against ultraviolet rays from the sun
(iv) The atmosphere is also an habitat for some microorganisms
2. The Hydrosphere: hydrosphere is the water mass of the earth. It is made up of streams, ponds, rivers, oceans, lakes and seas. It is 70% of the earth surface.
Importance of the Hydrosphere
(i) Hydrosphere provides water for domestic and industrial use
(ii) Hydrosphere creates employment
(iii) Hydrosphere can be used to generate electricity
(iv) Hydrosphere encourages tourism
3. The Biosphere: biosphere is the biological active part of the earth. Biosphere consists of plants, animals and organisms. There are aquatic and terrestrial biocycles
Importance of the Biosphere
(i) Biosphere produce plants which provide food for man
(ii) Biosphere provide energy source to man
(iii) Biosphere balances and purifies atmospheric gas
(iv) Biosphere provides raw materials for industries
(v) Biosphere creates employment for man through agriculture
The Internal structure of the Earth
The internal structure of the Earth is made up concentric layers: The Lithosphere
The Mantle or Mesosphere
The core or Barysphere
The lithosphere
The lithosphere is made up of two parts namely sial and Sima. Sial is 2.7 in density and made of granite. Sima is 3.0 in density and made basalts.
The Mantle (Mesosphere)
The Mesosphere lies beneath the lithosphere. The mesosphere is very thick and rich in mineral called olivine. The mesosphere is the middle layer which surrounds the core.
The Core or Barysphere
The Barysphere is the inner most layer believed to be fluid because of the high temperature. It is made up of a mineral constituent known as Nickel.
The Earth is made up of four distinct layers:
- The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth.
- The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.
- The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt.
- The crust is the outer layer of the earth. It is a thin layer between 0-60 km thick. The crust is the solid rock layer upon which we live.
There are two different types of crust: continental crust, which carries land, and oceanic crust, which carries water.
Mantle
Earth’s mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone
Earth Crust
Earth’s crust is made up of several elements: oxygen, 47 percent; silicon, 27 percent; aluminum, 8 percent; iron, 5 percent; calcium, 4 percent; magnesium, potassium and sodium, 2 percent. The crust ranges from 5–70 km (~3–44 miles) in depth and is the outermost layer. The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and are composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt. The thicker crust is continental crust, which is less dense and composed of (felsic) sodium potassium aluminium silicate rocks, like granite. The rocks of the crust fall into two major categories – sial and sima.
Earth Core
At the center of the Earth is the core, which has two parts. The solid, inner core of iron has a radius of about 760 miles (about 1,220 km). It is surrounded by a liquid, outer core composed of a nickel-iron alloy. It is about 1,355 miles (2,180 km) thick. The inner core spins at a different speed than the rest of the planet. This is thought to cause Earth’s magnetic field. When charged particles from the solar wind collide with air molecules above Earth’s magnetic poles, it causes the air molecules to glow, causing the auroras — the northern and southern lights.
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