Artificial Sources to Study Earth’s Interior

2 years ago
Atiqur Rahman
7 minutes

Artificial sources are those sources which are derived from mathematical assumptions and calculations. Important among them are:

  1. Density
  2. Pressure
  3. Temperature

Density

The earth is made up of various types of rocks. Rocks are composed of minerals. Rock may be composed of one mineral or many minerals. The characteristics and properties of the minerals determine the rocks.

The rocks under our feet while walking can be examined well in our laboratory. The rocks of various places are not alike but are different. The rocks lying in our agricultural field are other than the mined rocks. It could be different types like igneous or sedimentary, or metamorphic.

The rocks of the earth’s surface are different from the interior. Studying the density is one way to know it. The density is the property of the rock’s compactness. When the molecules of the rocks are very close, it is denser. In other words, it is defined as the relationship between the mass of the rock and how much volume it occupies. Thus, a rock with greater mass and lesser volume will become denser, but the density is lower when the mass is less and the volume is more. Therefore, density is equal to the mass of the rock divided by its volume.

D = m / v

Where

D = Density,

m = mass of the rock and

v = volume of the same rock

This formula expresses the result received as that much gram/cm3.

For the first time, British scientist Henry Cavendish (1798) probably attempted to calculate the earth’s density based on Newton’s law of Gravitation. He found it to be 5.48 gm/cm3. Poynting (1878) calculated the earth’s density and found it to be 5.49 gm/cm3.

The density of the rocks found at the surface rocks: 2.7 – 2.9 gm/cm3

The density of rocks found at the sea floor is around: 3.0 gm/cm3

It is quite obvious that the central part of the earth is more than: 5.5 gm/cm3

The average density of the earth: 5.52 gm/cm3

The density calculated at different depths in the earth’s interior is given in the following Table.

Depth in kmDensity in gram/cm3
(Surface/ Sea Level) 02.70 to 2.90
1003.38
Ite 5003.85
10004.58
20005.12
28905.56
29009.90
400011.32
500012.12
550012.92
637113.09
Density of Rocks at Different Depths in the Interior

It is also very clear through the Table that the density of the innermost part of the earth is around 13 gm/cm3. The increase in the density in the earth’s interior is not a continuous affair but changes very abruptly at different depths. The changing density at different depths in the interior may very clearly be seen at a glance in Fig.

Density in the Interior
Density in the Interior Source

Pressure

It is obvious that the density of the rocks in the interior is greater. It is scientifically proven that the density of matter is increased when it is compressed. Earlier, it was assumed that the density of the interior rock is greater due to the increasing pressure of the rocks lying above. To some extent, this assumption is true, but it is also a universally proven fact that the density of the rocks cannot be increased beyond a certain limit simply by compression or more pressure.

Hence, the inference that the increasing pressure is the reason for greater density is not true. The higher dense material of the interior can be explained through the constituent of the rocks. It is now confirmed that the core is composed of essentially heavy metallic materials which have higher density. The pressure in the interior keeps on increasing with depth (Fig).

Pressure in the Interior
Pressure in the Interior

Temperature

With the advancement in technology and know-how to use the minerals, mining activities started. We have been digging the earth for many centuries. But the deeper mining and oil exploration has led to drilling the crust to a much deeper level in recent times.

Our observations record a rate of increase in temperature, and it is about 3°C per 100-meter depth or about 30°C per km. If we calculate the temperature at this rate, the earth’s core would witness a temperature of more than 1,90,0000 C. it is unimaginable. Probably, this much of high temperature would melt the entire earth.

The above calculation has not taken the increasing pressure into account. A recent experiment conducted and calculated by scientists suggests that the inner part of the earth, the core, has about 50000 C temperature with a variation of 5000 C plus or minus. Hence, these two temperatures are contradictory to each other.

The temperature increase observed in the earth’s top layer is not constant. The rate may be higher near the surface for a few km, but it is not true for the much deeper part of the earth.

The above conditions could very well be explained by the presence of radioactive minerals in the top layers of the crust. Granitic rocks are very well known for the abundance of radioactive minerals like uranium and thorium. The higher temperature in the granitic layer was found accounted due to chemical disintegration. The process of fission and fusion of these minerals generates a huge amount of heat. This leads to greater temperature in this zone of the earth’s strata.

With increasing depth, the availability of radioactive minerals is less and hence, lesser temperature. Therefore, there is a decrease in the rate of temperature with depth. The observed temperature and temperature needed to melt the rock at different depths are shown by a graphical representation in Fig.

Observed and Melting Temperature in the Interior
Observed and Melting Temperature in the Interior

Relationships of Density, Pressure and Temperature with Depths

We have already deliberated above about the density, pressure and temperature in the earth’s interior. From these discussions, it is clear that all three components are increasing with increasing depth. Their increase is not uniform continuously but with changing rates. The reasons for their increase are already explained while dealing with those components. Their relationships are very clearly seen in Fig.

Relationships of Density, Pressure and Temperature with Depths
Relationships of Density, Pressure and Temperature with Depths

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  2. Epeirogenic Earth Movements
  3. Orogenic Earth Movements
  4. Cymatogenic Earth Movements
  5. Concept of Stress and Strain in Rocks
  6. Folds in Geography
  7. Fault in Geography
  8. Mountain Building Process
  9. Morphogenetic Regions
  10. Isostasy: Concept of Airy, Pratt, Hayford & Bowie and Jolly
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  12. Plate Tectonics: Assumptions, Evidences, Plate Boundaries and Features Formed
  13. Volcanoes: Process, Products, Types, Landforms and Distribution
  14. Earthquakes: Processes, Causes and Measurement
  15. Plate Tectonics and Earthquakes
  16. Composition and Structure of Earth’s Interior
  17. Artificial Sources to Study Earth’s Interior
  18. Natural Sources to Study Earth’s Interior
  19. Internal Structure of Earth
  20. Chemical Composition and Layering of Earth
  21. Weathering: Definition and Types
  22. Mass Wasting: Concept, Factors and Types
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  24. Davis Model of Cycle of Erosion
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  26. King’s Model of Slope Development
  27. Alan Wood’s Model of Slope Evolution
  28. Strahler’s Model of Slope Development
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  30. Elements of Slope
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