Human mind is always eager to know about the planet earth, but we have limited resources to know and there are always some boundaries which we can't cross.
Curiosity to know about what is inside the earth is always been there, in human history we have did the deepest man made whole to know what is inside the earth and how the interior of the earth looks like.
Deepest hole that we have dig is Kola superdeep borehole (Russia) but we stopped after digging 12.2 km because of the increasing heat and seismic waves.
What material is the Earth's interior made up of, in what state is it? There are many questions that man has always been curious to know.
In general we divides the earth in four concentric layers that are crust, mantle, outer core and inner core. Depth of the outer layer "crust" is 33 km and crust is made out of different different rocks and apparently it is in the solid form. Let's dig a bit deeper and move to the second layer, which is "mental" and the depth of mantle is 2900 km then comes the third layer "outer core" which is around 2900 km - 5120 km and the last one is the "inner core", and the depth of the inner core is 5120 km - 6371 km, which is the central part of the earth.
Everything that we know about the interior of the earth. We have the limited sources and we can mainly divided them into two parts.
(A) Artificial Sources
(B) Natural Sources
(A) Artificial Sources
The artificial sources that we have to know about the interior of the earth, that are :- 1. Density, 2. Pressure and 3. Temperature
1. Density
The density inside the earth is different from the surface, initially from the crust it starts from average 2.7 and when it reaches the mantle layer it becomes 5.7 and it goes up because after 2900 km the core starts and the density becomes 9.7, and for the centre it is goes around 11-12 gram per cubic centimetre. The density in the core part is still debatable amongst the scholars, according to K.Bullen and S.L Subbotin it can be around 17.9 gram per cubic centimeter.
Initially Scholars thought that the pressure in the interior part makes the core dense but in the lab experiments it has been proven that after applying a immense pressure on rocks the density doesn't change. Then there is another thought that says that the density of the earth's core is dense because it is made up of material that have the high density, mainly it is believed that the core of the Earth is made up of iron and Nickel because they have high density.
(i) The earth behaves like a giant magnet because of that the earth has the magnetic field around it which proves that the earth's core must be made up of magnetic metals like iron and nickel.
(ii) We never found any meteoroid which is made up of a metal which is not available on the earth and most of the meteors are made up of Nickel and iron.
2. Pressure
Inside the earth at any point a weight on per cm square is called pressure. The pressure generate because of the weight and this pressure becomes 13000 times much comparable with the surface and in 50 km depth. Which means the atmospheric pressure in 50 km depth becomes 13000 times more powerful and for the centre of the Earth this pressure goes up to 3500000 - 4000000 atmospheric pressure, which means the pressure inside the earth is so much.
Some scholars says that this pressure exists not because of weight but because of heavy rocks.
3. Temperature
In general when we inter towards the interior of the earth the temperature increases and this increment is after every 32 meter the temperature goes 1 Degree Celsius up.
If we proceed with this calculation, then the temperature of the core of the earth will be 200000 degree celsius. But in reality this doesn't happen and test shows that the rate of increase in temperature decreases with depth, and based on this calculation the temperature of the earth's core should be 2000 degree celsius.
In the year 1897 K elvin was the first person who talked about temperature inside the earth, according to him initially Earth's temperature was 6000 degree Celsius and gradually it started cooling down and the surface becomes solid, but the core is still hot, most of the Kelvin's calculations were wrong because in his time period the radioactivity was not discovered. The radioactive elements are continuously disintegrating inside the earth keeping all these things in mind it's clear that the interior of the earth should be in liquid or gas state.
If the matter inside the earth will be in a liquid state due to high temperature, then we also cannot ignore that the high pressure and density will make the substance more rigid than solid due to which they will have the properties of both liquid and solid.
That's why this substance will have properties like wax, so if this material is hit it becomes hard and by applying lite pressure it flows like a liquid. All these factors tells us that the Earth acts like a solid and in the ideal condition acts like a liquid and when the pressure decreases on the upper layer the lower layer converse into liquid which is proven by liquid lava.
(B) Natural Sources
The Natural Sources that we use to understand the interior of the earth are
1. Volcanic Eruptions
2. Seismology
1. Volcanic Eruption
When a volcano erupts and Magma comes out the liquid Lava makes us to believe that there is liquid metal inside the earth. Most of the volcano has their sources in depth of 40 to 50 km, these sources are called magma chambers that's prove that the interior of the earth is in the liquid form but some Scholars says that it's not possible for the substance to be in the liquid form because of the high pressure which increases the melting point.
But it is possible that when there are some cracks on the earth's surface it will decrease the pressure, so the melting point will also be decreased and which will lead to volcanic eruption.
It shows us that even we can witness the volcanic eruption, but it's not enough to give us all the answers.
2. Seismology
Earthquakes are the important source to know about the interior of the earth, when earthquake originates it produces the seismic waves, studying about the seismic waves gives us lots of information about the interior of the earth.
