Structure of the Earth’s Interior. Do you REALLY believe? ? ?. All the planets of the solar system came out of the Sun!! Humans have been able to peep into the mantle!! All the Interior of the Earth is in molten state!! The Earth has only one North Pole!!. How was Earth formed?.
Big Bang Theory
Solar Nebular Theory
-14 billion years ago,
-huge explosion -the Big Bang.
-the universe was very hot and dense and filled with energy.
-As space expanded, the temperature began to fall and the first particles of matter formed from the energy.
-After more than 1 billion years, the first stars and galaxies had formed. --The Solar System, including our Earth, formed about 4.6 billion years ago.
Due to the gravity of the nebula, some part of the sun was scraped off in the form of a large mass of dust particles and tiny planetary matter.
The planetary matter followed the nebula for a distance but could not keep pace with the very fast moving nebula and was hence suspended in space.
Initial motion given to the planetary matter was now controlled by the gravity of the sun because of which the material started revolving around the primitive sun.
Because of the revolution of the planetary material around the sun, there was a churning effect resulting in the accretion (getting together) of the material forming the early meteorites.
As the asteroids were attracted towards each other due to gravity, they collapsed into each other forming the early planetoids
As a result of tremendous impact velocities of the asteroids, a lot of friction and heat was generated because of which the early planetoids were in a molten state.
Verification of this assumption is very difficult. The deepest hole dug into the earth is only 16 km deep. Hence direct methods cannot be used to find out about the interior of the earth.
HOW TO STUDY THE MYSTERIES OF THE INTERIOR OF THE EARTH??
A wave is a series of disturbances caused in the particles of any medium due to the propagation of energy.
Watch Video: http://www.youtube.com/watch?v=9J6EHnra7Mo&NR=1
Watch Video: http://www.youtube.com/watch?v=7NqmHtIjCJ0&NR=1
Following is a description of the experiment conducted by E Mohorovicic, a Dutch physicist who proved the existence of the crust and the mantle.
Consider the figure above. E is a point on the earth’s surface where an artificial explosion is created. As a result of this, seismic P waves travel in all directions. One such P wave travels along the path EB. Upon reaching the crust-mantle boundary (the Mohorovocic Discontinuity, or simply, the Moho), it is partly refracted into the mantle and partly reflected back to the surface of the earth where it is recorded at a seismic recording station R.
ER distance = 160 km
Explosion at-09.00.00 am
1st set of P waves reach R at 09.00.32 am
2nd set of P waves reach R at 09.00.40 am
Speed of waves= 160/32= 5 km/sec
Time taken to reach from EB to BR=
40 seconds * 5 km= 200 km
EB= BR= 100 km
Therefore by ASA, proved.
According to Pythagoras Theorem, EB2=EA2+AB2
= 10000= 6400+AB2
= 3600 kms = 60 km ( Thickness of the crust)
Several such experiments indicate that the thickness of the continental crust is 70 to 80 km while the thickness of the oceanic crust is in the range of 10 to 20 km. On an average, the crust can be said to be about 60 km in thickness.
An explosion is created at point E on the earth’s surface due to which S waves travel in all directions. Most of them are refracted by the mantle and are received at points R1, R2, R3 and R4. Some of these S waves are blocked by the core, which suggests that it is in a liquid state. This is why no S waves reach the seismic recording station R5.
The part of the Earth between the points R3 and R4 (including R5) is called the S wave shadow zone and the angle formed between these points at the centre of the earth (angle R3CR4) is always equal to 150º.
Watch Video: http://www.youtube.com/watch?v=v_1QcI3BWRk&feature=related
A point to be noted here is that while S waves are blocked by the core (outer core), P waves are received at R5 and all other stations in the shadow zone. P wave velocities are not uniform throughout the core, which indicates that there is a solid inner core (where the velocity of P waves increases).
The result that we get using this method is that the radius of the core is 3500 km. Since the radius of the Earth is 6400 km, the thickness of the mantle would be 2900 km.
1. The thickness of the oceanic crust is in the range of 10 to 20 km. Therefore magma from the mantle can directly erupt through submarine volcanoes. A chemical analysis of this lava gives us the composition of the mantle.
2. The velocity of P waves in the mantle is about 8 km/s. Scientists passes P waves through several rocks present on the earth and found that the velocity of P waves equals to 8 km/s in only three rocks, viz. Peridotite, Dunite and Eclogite. It is interesting to note that these rocks are found mostly in the vicinity of submarine volcanoes.
3. It is believed that the primitive earth formed as a result of several meteoritic impacts. It is possible that the composition of the mantle is similar to the meteorites falling on the earth even today. A chemical analysis of meteorites gives results similar to the two methods discussed above.