INTRODUCTION
THE EARTH
EARTH is the third planet from the sun and is the largest of the terrestrial planets.
The ‘Earth’s’ name comes from the Anglo-Saxon word “erda” which means ‘ground or soil”.
THE CONCEPT OF THE STRUCTURE OF THE EARTH
The Earth’s structure is composed of two parts namely, internal structure and external structure. The internal structure is composed of three concentric zones called core (barysphere), mantle (mesosphere) and crust.
The external structure consists of atmosphere, hydrosphere and biosphere.
I. THE INNER ZONES (INTERNAL STRUCTURE OF THE EARTH)
The inner zones of the Earth include; the crust, mantle and the core.
These layers are made of materials that increases density towards the centre because of differences in pressure and temperature.
The less dense rocks float on the top of the denser zones which are further down. The heavier elements like IRON and NICKEL are settled at the core of the Earth.
A. THE CRUST/LITHOSPHERE
– This is the outermost of all the zones in the interior of the Earth. It is sometimes called the Lithosphere. – It consists of two layers, namely the SIAL and the SIMA. These layers form the crust which varies in thickness from 8km to 50km due to variations in landforms.
I. SIAL
SIAL is the upper layer of the crust consisting of SILICA and ALUMINIUM.
It has an average density of 2.7gms/cc (grams per cubic centimetre).
It forms the continents.
II. SIMA
SIMA is the layer below the SIAL.
Its rocks are basalt and it consists of SILICA and MAGNESIUM.
Its average density is between 2.8 and 3.0gms/cc.
The SIMA forms the ocean floor.
– SIAL and SIMA are separated by a zone called Conrad discontinuity, discovered by Victor Conrad. – The crust is separated from the mantle by a zone/layer called Mohorovicic discontinuity, discovered by Andrija Mohorovicic.
The structure of the Earth’s crust is on continuous changes caused by internal and external forces operating on and within it.
Continental drift theory states that before the formation of the present continents, the Earth was one SIALIC land mass called PANGAEA. This super continent, PANGAEA was surrounded by a SIMA-floored ocean called PANTHALASA. It started to break up into the present continents around 200 million years ago, where it was divided into GONDWANALAND in the South and LAURASIA in the North during the late Pre-Cambrian era about 200milion years ago. These two blocks, were separated by a long narrow sea called TETHYS. The two masses continued breaking into continents that exists today.
THE MANTLE/MESOSPHERE
This is the layer beneath the crust.
It is made up of very dense igneous rocks of iron, silicon, aluminum and magnesium.
It has a thickness of about 2900km and an average density of between 3.0 and 3.4gm/cc
It is the largest of the three regions. **
The mantle is subdivided into two main layers, the upper mantle and the lower mantle.
a. THE UPPER MANTLE
The upper mantle is approximately 650km thick.
It is rigid and combines with the crust to form Lithosphere
The top thin portion of the upper mantle below the CRUST is in a semi-molten state which forms a layer called Asthenosphere
ASTHENOSPHERE
It is a thin layer found between 100km to 200km below its surface.
Its rocks are less rigid and more plastic
Its temperature is about 1600 C
It is involved in plate tectonic and isostatic adjustments
b. THE LOWER MANTLE
The lower mantle has a thickness of approximately 2300km.
Its rocks exist in solid state, because of weight of overlying rock materials.
The convection currents generated in the lower mantle due to high temperature, trigger/initiate various internal movements.
The upper mantle and the lower mantle is known as Rapetti Discontinuity.
The mantle is separated from the core by a sharp boundary called the Gutenberg discontinuity, discovered by Weichert (Beno) Gutenberg.
C. THE CORE/BARYSPHERE/CENTROSPHERE
This is the innermost part of the Earth.
It has the diameter (thickness) of about 6,900km and consists of Nickel and Iron (NIFE).
The core is divided into two parts/layers known as the outer core and the inner core.
THE EARTH
EARTH is the third planet from the sun and is the largest of the terrestrial planets.
The ‘Earth’s’ name comes from the Anglo-Saxon word “erda” which means ‘ground or soil”.
THE CONCEPT OF THE STRUCTURE OF THE EARTH
The Earth’s structure is composed of two parts namely, internal structure and external structure. The internal structure is composed of three concentric zones called core (barysphere), mantle (mesosphere) and crust.
The external structure consists of atmosphere, hydrosphere and biosphere.
I. THE INNER ZONES (INTERNAL STRUCTURE OF THE EARTH)
The inner zones of the Earth include; the crust, mantle and the core.
These layers are made of materials that increases density towards the centre because of differences in pressure and temperature.
The less dense rocks float on the top of the denser zones which are further down. The heavier elements like IRON and NICKEL are settled at the core of the Earth.
A. THE CRUST/LITHOSPHERE
– This is the outermost of all the zones in the interior of the Earth. It is sometimes called the Lithosphere. – It consists of two layers, namely the SIAL and the SIMA. These layers form the crust which varies in thickness from 8km to 50km due to variations in landforms.
I. SIAL
SIAL is the upper layer of the crust consisting of SILICA and ALUMINIUM.
It has an average density of 2.7gms/cc (grams per cubic centimetre).
It forms the continents.
II. SIMA
SIMA is the layer below the SIAL.
Its rocks are basalt and it consists of SILICA and MAGNESIUM.
Its average density is between 2.8 and 3.0gms/cc.
The SIMA forms the ocean floor.
– SIAL and SIMA are separated by a zone called Conrad discontinuity, discovered by Victor Conrad. – The crust is separated from the mantle by a zone/layer called Mohorovicic discontinuity, discovered by Andrija Mohorovicic.
The structure of the Earth’s crust is on continuous changes caused by internal and external forces operating on and within it.
Continental drift theory states that before the formation of the present continents, the Earth was one SIALIC land mass called PANGAEA. This super continent, PANGAEA was surrounded by a SIMA-floored ocean called PANTHALASA. It started to break up into the present continents around 200 million years ago, where it was divided into GONDWANALAND in the South and LAURASIA in the North during the late Pre-Cambrian era about 200milion years ago. These two blocks, were separated by a long narrow sea called TETHYS. The two masses continued breaking into continents that exists today.
THE MANTLE/MESOSPHERE
This is the layer beneath the crust.
It is made up of very dense igneous rocks of iron, silicon, aluminum and magnesium.
It has a thickness of about 2900km and an average density of between 3.0 and 3.4gm/cc
It is the largest of the three regions. **
The mantle is subdivided into two main layers, the upper mantle and the lower mantle.
a. THE UPPER MANTLE
The upper mantle is approximately 650km thick.
It is rigid and combines with the crust to form Lithosphere
The top thin portion of the upper mantle below the CRUST is in a semi-molten state which forms a layer called Asthenosphere
ASTHENOSPHERE
It is a thin layer found between 100km to 200km below its surface.
Its rocks are less rigid and more plastic
Its temperature is about 1600 C
It is involved in plate tectonic and isostatic adjustments
b. THE LOWER MANTLE
The lower mantle has a thickness of approximately 2300km.
Its rocks exist in solid state, because of weight of overlying rock materials.
The convection currents generated in the lower mantle due to high temperature, trigger/initiate various internal movements.
The upper mantle and the lower mantle is known as Rapetti Discontinuity.
The mantle is separated from the core by a sharp boundary called the Gutenberg discontinuity, discovered by Weichert (Beno) Gutenberg.
C. THE CORE/BARYSPHERE/CENTROSPHERE
This is the innermost part of the Earth.
It has the diameter (thickness) of about 6,900km and consists of Nickel and Iron (NIFE).
The core is divided into two parts/layers known as the outer core and the inner core.