Internal structure of the earth

Internal structure of the earth

The evidence of the transverse,longitudinal and surface waves set in motion during an earthquake has led to the conclusion that the globe or the earth consists of four layers one above the other if we proceed from the core of the earth outwards or one below the other if we proceed downwards from the crust of the earth.

Layers of the earth 

There are mainly three layers of the earth

• The crust
• The mantle
• The core 

According to German scientist Gracht

• SIAL
• SIMA
• NIFE

According to Jeffrey

• Top layer
• Middle layer
• Lower layer

According to Prof. Holmes

• The crust
• The substrutum
• The core

Some scientist have divided the layers respectively

• Lithosphere
• Pyrosphere
• Barysphere

Some images about the layers are given below

The top most layer of the earth which forms the earth crust is the lightest layer.On this layer which is also known as lithosphere the main earthquake waves travel at a nominal speed of 3.5 miles per second while the speed of transverse waves is still less only 2 miles per second.The specific gravity of this layer is only 2.7 and its mean thickness is about 20 km.It is made of granite rocks,silica and aluminium predominate.Therefore,It is named in short SIAL.

Next this or below this top layer is the region of basalt rocks and this is heavier then the topmost layer.The specific gravity is 3.5.Through this layer the main waves have the speed of 4-4.5 miles per second while the transverse waves move at a speed of 2-2.5 miles per second.In this layer silica and magnesium elements dominate and it is known as SIMA.The upper region of this second layer is a short of mixture of SIAL and SIMA.SIMA layer forms the bottom of the ocean and is known as the pyrosphere.

Finally comes the central core of the earth.This is situated at a depth of 1800 miles.This central mass is made of nickel and iron,therefore,it is known as in short NIFE.Its specific gravity is 8.The core contains a third of the entire mass of the earth.It is made of very hard minerals and the materials of which it is made are very dense about ten times dense as the rest of the earth.But because of instance heat and pressure this core is not solid ,nor is it liquid.It is directly not gaseous.Its structure is elastic and viscous.Because its high specific gravity the main or longitudinal waves are unable to pierce it while its viscousness is elasticity prevents the transverse waves from passing through it.Evidence of elasticity and viscousness is provided by the rocks involved in mountain building and now exposed by denudation.These rocks seem to have flowed without melting,It is rigid but it is not hard.   

Wednesday, January 12, 2011

The earth and its formation

The earth is a 3rd planet of the solar system.It is only one of the planet which is suitable for life.This planet is full of different living or                                                                                                                                         Our planet earth began approximately 4.6 billions years ago when a cloud known as solar nebula collapsed forming protostars and planetary systems.Life on earth began approximately 2 billion years later.Since the evolution of first life in the form of an aquatic anaerobe ,different kinds of organisms have evolved,prospered and died.Among all the planets of the solar system only the earth has atmosphere and it has necessary oxygen and nitrogen which are most important elements for living organisms.Without these two gasses there are Ar,Carbon-dioxide,Ne,He,Kr,Xe,H,Methane,Nitrusoxide etc. and dust and water vapor in the earth.These gasses and temperature are suitable to live in the earth.The earth has only one satellite named the moon.
       The rains comes from the sky on the earth,the rivers flow over by their own minds,the highest mountain range,ocean,plateau,plain land,volcano,grassland etc. the beautiful nature have made the earth as a haven.
     Book reference

1. Essentials of ecology and environmental science-S.V.S. RANA
2.  PRAKRITIK BHIUGOL-Dr.Rejuan hossain bhhuian, Md. Khayrul Anam

Structure of the atmosphere

Structure of the Atmosphere

The vertical  structure consisting of several layers of the atmosphere, determined primarily by the phenomena that occur there,are separated from one another by change of the slope of the graph of temperature vs altitude.There are 4 basic layers of atmosphere.They are given below-

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere

The layers are discussed below-
Troposphere

The lowest layer of atmosphere in which living organism operate is called troposphere.It is the region of strong air movements and cloud formation characterized by sleady decrease in temperature.It is a mixture of several gasses which is remained fairly in abundance.However water vapor and dust occured in troposphere in extremely variable concentration.The average temperature of this layer is about 15 degree celcious,It is the suitable layer for living organisms.
Sratosphere
Stratosphere is the air mass extending from the upper most level of the troposphere to upper most level of stratosphere,about 50 km above surface of the earth.Ozone present there forms an ozone layer called ozonosphere.It is formed full from oxygen through a photochemical reaction where oxygen molecule splits to form atomic oxygen.




The atomic oxygen combines with molecular oxygen and ozone is formed.
Although the reaction are reversible in nature however percentage of ozone remain constant.


It forms an umbrella called ozone-umbrella that absorbs the UV radiation coming from the sun.Moreover,it serves as a blanket an reducing the cooling rate of the earth.Therefore am equilibrium between ozone and rest of the air is a significant factor of the environment.The line at the end of the stratosphere and start of the mesosphere is called stratopause where we see the subsonic aircraft.


Mesosphere

Above of the stratosphere the layer mesosphere is found.It is characterized by cold temperature and low atmospheric pressure.The temperature drops reaching a minimum of -95 degree centigrade 80-90 km above the earth surface.
Thermosphere

Above the mesosphere,is thermosphere extending up to 500 km above the earth surface.It is characterized by an increase in the temperature from the mesosphere  upper zone to the thermosphere where ionozation of molecules oxygen occur is called the ionosphere.
       
The another layer of the atmosphere is exosphere.In the atmosphere above the ionosphere is called exosphere of the outer space which lacks of atmosphere except that of hydrogen and helium and extends 32190 km from the surface of the earth.It has very high temperature due to solar radiations.