Explain the composition of the Earth’s Womb.

There are the following ideologies about the interior of the earth

(1) The Innermost Hypothesis of the Earth’s Interior

German geophysicist Suess proposed the idea that the melting point of any substance increases with an increase in pressure, but experiments have shown that this is only possible up to a certain extent. No mineral substance can remain solid at high temperatures. This idea is supported by volcanic eruptions, igneous rocks, and hot springs. British scholar Pitt and German geographer Ritter also supported this idea. However, it has been argued that during tides, the Earth’s spherical body acts as a solid body, and earthquake waves can only reach very deep if the Earth is a solid spherical body. Other celestial bodies, such as the Earth, are also solid. In 1936, Lehmann proved with seismological evidence that the center of the Earth can be solid.


(2) Hypothesis of a liquid inner core

The hypothesis of a liquid inner core was proposed by Laplace, supported by the occurrence of volcanic eruptions and the interruption of earthquake waves. In 1890, Weichert proposed the idea of a liquid inner core, which was later supported by geologist Oldham. However, there are also opposing views against this hypothesis:

  1. To generate tides in the ocean, there must be a solid spherical body of 400 km thickness below the hydrosphere. If the inner core were liquid, then the tides would rise on the surface of the earth, but this does not happen.
  2. The solid layer above would have become solid and dense over many ages, resulting in a continuous decrease in volcanic eruptions. However, this is not observed.
  3. A liquid cannot remain at the bottom as it solidifies, the bottom shell would settle down due to greater gravity. This makes the idea of a liquid inner core untenable.

The Swedish scientist Arrhenius proposed that the Earth is made of metals and that its very deep part is filled with metals, with the upper part being solid, the middle being liquid and the lower part being in the gaseous state. However, there are two difficulties in accepting this statement:

  1. During tides, the Earth mass behaves like a solid body.
  2. Earthquake waves travel as deep as they can in a solid body.

(3) Gaseous Innermost Hypothesis

Based on the rocks of the Earth’s crust and the density of the Earth, Newton determined that the attraction power increases in proportion to the amount of matter in substances and decreases in proportion to the distance between them. According to this law, the density of the whole Earth is 5.5, that of the crust is 2.7, and that of the central part is 8. This concludes that the interior of the Earth is made up of very heavy materials. The solidity of the Earth’s sphere, its magnetism, and the significant fraction of iron and nickel compounds in meteors also support this fact. Therefore, the notion of a gaseous innermost, introduced by Laplace, appears to be impractical.

(4) Suess’s Principle

The fibrous part of the Earth’s outer rocks is mainly composed of silica, which contains minerals like feldspar, mica, etc. The density of rocks made of silica varies greatly because there are two types of fibrous rocks. The first type is lighter silica rocks, and the second type is dense silica rocks. These points confirm the idea of a German scientist named Suess that there is a layer of simple granite-like material called Sial below the sedimentary rocks. Sial contains a predominance of silica and aluminum, and its density varies from 2.7 to 2.9. It makes up most of the continents. Below Sial is a substance of high density, which is rich in silica and magnesium, and we call it Sima. Sima retains only the original igneous rocks that are heavier. The representatives of Sima are rocks like basalt and gabbro, and its density ranges from 2.9 to 4.75. Sima forms most of the oceanic crust, but it is also located under the continents. The central part of the Earth is made up of iron and nickel and is called Nife.

Suess named the central part of the Earth Nife after Sima. The density of Nife’s rocks is 8 to 11, and iron and nickel predominate.

According to Suess, the continents are made of Sial, and the lower part of the continents and the ocean floor are made of Sima.

Division of the earth’s layers

Based on earthquake waves, the Earth can be divided into three layers:

  1. Lithosphere – Its thickness is considered to be up to a depth of 100 km from the surface of the Earth. It is formed by light, watershed rocks dominated by granite, in which silica and aluminum metals predominate. The speed of the main waves of an earthquake in this layer is 5.1 km per second, and that of oblique waves is 3 km per second. The density of its rocks is 2.7.
  2. Upper mantle – This is the intermediate layer of the Earth’s mantle which is believed to be from 100 km to 2,900 km in depth. These rocks are rich in silica and magnesium. Waves move 6 to 7 km per second, and oblique waves move at 3 to 4 km per second. The density of this region’s basalt rocks is 3.5.
  3. Core – This part falls from 2,900 km in depth to the center of the Earth. It is one-third of the Earth. Its density is 8 to 11, and it is predominated by iron or nickel. Oblique waves cannot enter this layer, and the speed of the dominant waves decreases upon entering the liquid. This part appears elastic, soft but firm.

Based on current investigations, it is concluded that the inner part of the Earth is not entirely composed of liquid matter. In the lowest central part, there is a solid part with a 1,290 km radius, which has a density of 18. The fluid silicate formed in the center is about 2,250 km thick.

Experimental studies of the compressibility of rocks in geophysics and meteorological evidence support the above hypothesis.

Jeffrey’s theory and earthquake waves

Some scientists have estimated the Earth’s internal composition by studying earthquake waves, based on the speed of these waves in solid and soft rocks. They have identified three layers of rocks – the upper, intermediate, and substratum. The upper layer is about 15 km thick and is composed mostly of granite, which includes sedimentary, metamorphic, and igneous rocks. The density of this layer is low, around 2.7. The speed of the Pg waves in this layer is 5.4 km per second, and the Sg waves travel at 3.3 km per second.

The intermediate layer, which is 20 to 30 km deep, is dominated by basalt. It has a definite chemical composition in the molten state, which can become fibrous by mixing different minerals under pressure and physical condition, or it may remain as a liquid when changing to a solid state. The speed of the main waves in this layer is 6 km per second, and the speed of the secondary waves is 4 km per second. The basalt layer is about 5 km thick, and the sediments of the oceans are based on basalt.

Beneath the basalt layer, there is a mantle layer up to a depth of 2,900 km, where geologist Mohoro Visit found a boundary between the mantle rock and the Earth’s surface. Mohoro Visit discovered a change or discontinuity in the earthquake waves in this belt at 35 km, which was named Moho. The density of this layer is 3.5, while the density of the lower part of the mantle-shell belt is 5.7.

The substratum includes the outer-ground core, which is found up to 5,100 km from the mantle layer. The density of its lower part is 15.2. After this, up to 6,370 km from the center of the Earth, an internal ground core is found, which has a density of 17.2. The predominance of iron and nickel is found from the layer of mansard to the center of the Earth. This part appears flexible and soft but firm.

American geologist Daly and Scottish mathematician Jeffrey believe that this part is made of basalt, las, or tachylite, while Bergen and Holmes think it is made of amphibolite. However, the substratum is believed to be made of dense materials like basalt, in which there is an abundance of olivine and minerals in a bright state. The study of seismic waves has been of great help in understanding the internal structure of the Earth.

Leave a Comment