Mankind tried to understand the internal structure and external structure of the earth from the immemorial times. But these theories were more likely related to legends and myths connected with divine intervention, but not with science. For example, the ancient Egyptians believed that the whole heavenly sphere was supported by the goddess of the sky, and the Sun was traveling across the sky in a boat. The inhabitants of ancient Babylon perceived the Earth as a mountain on the slope of which they lived. From the south, it was surrounded by the sea. According to their ideas, a solid sky rests on the sea, along which the sun moves, and under the earth – the abyss. At night, the Sun comes down to this abyss and in the morning rises from the east.
The first scientific hypothesis is the famous theory about the flat Earth, which has been famous since the times of Mesopotamian culture. The planet was depicted as a flat disk surrounded by the ocean.
The Earth from the ancient point of view
In ancient culture, in the 6th century BC Greeks tended to round shape, and in 330 BC famous philosopher Aristotle confirmed the idea of a spherical Earth and gave the first evidence base. Claudius Ptolemy supplemented this evidence base, justifying it by the fact that the mountains are visible from the sea as if protruding from the water, which is possible if they are partially obscured by the water surface. At the same time, interest in geological research, minerals and metals appeared.
But the real breakthrough occurred only in the 16-17th centuries. Edmund Halley in 1692 proposed the theory of the “the hollow world.” He argued that inside there is a cavity, that is, a certain core whose thickness is 800 km and between these spheres, there is an air gap. In order to avoid the effect of friction, the inner sphere must be held in place by gravity. The model displayed two concentric shells around the core.
Then the scientists decided to consider the authenticity of the Bible. It was important for researchers to calculate the real age of the planet and find evidence of the flood. It was here that they began to consider fossils and develop a system for classifying the dating of layers.
The main date that becomes crucial in Earth science
In 1774, Abraham Werner presented in his writings a detailed system for the identification of certain minerals, based on their external characteristics.
In 1741, the first post in geology appeared in the National Museum of Natural History of France. After 10 years, the term “geology” came into use.
In the 1770s In the first place in the studies comes chemical analysis. One of the important tasks was to study places for the presence of liquid floods in the past.
In the 1780s scientists developed the theory that the layers were created by fire. According to theory, the planet was formed due to solidification of the molten mass. The followers of this hypothesis were called plutonists.
In the 19th century, the industrial revolution greatly influenced geology. Scientists began to realize that the age of minerals can be calculated geologically.
In the 20th century, radiometric dating appeared. Then they thought that the planetary age reaches 2 billion years. In 1912, Alfred Wegener put forward the theory of continental drift. That is, once all the continents were one. Later this was confirmed by geological analysis of samples.
In the 20th century, seismology, the study of earthquakes and the passage of waves through the Earth were actively developed. That is what helped to understand the composition and get to the core.
In 1926, Harold Jeffries declared that the earth’s core was liquid. And in 1937 the Danish seismologist Inge Lehmann discovered the existence of a solid inner core of the Earth. So it was proved that the inner space of the planet is differentiated. That is, the structure is represented by layers. Remove one and get to the next one and each will have its own temperature and chemical composition.
Today, the Earth can be divided mechanically or chemically. The first method studies the liquid state. Here appears the lithosphere, the asthenosphere, and the mesosphere, the outer and inner core. But the chemical method, which discovered the crust, the mantle, and the core, became very popular. In the center of the planet is the inner core. It is surrounded by an outer core. Then the mantle is located. Above the mantle is the crust on which we live.
The crust is the outermost layer of the earth’s surface in which living organisms can exist. Its average thickness is only 33 km, while it is thinner under the oceans (from 4 to 20 km) and thicker under the continents (from 20 to 75 km). Accordingly, there are two types of crust – continental and oceanic, the structure of which is different. The uppermost part of the crust consists of sedimentary rocks, and remains of animals and plants that have long disappeared are often found in it.
Like the mantle, the core consists of two parts: the inner and the outer. The temperature of the inner core reaches 7700 Fahrenheit degree celsius (13892 degrees Fahrenheit), and the external one reaches 6000 degrees Celsius (10832 degrees Fahrenheit). The outer core is liquid, that is, its substance is in a molten state and is the source of the magnetic field of our planet. The hard part of the nucleus as it floats in the outer, liquid layer. Thanks to this movement, a magnetic field arises around the earth. It protects life on our planet from the detrimental effects of cosmic particles, for example, ionized (charged) particles of the solar wind.
The diameter of the inner core is small – about 1500 km. Very little is known about the core: samples of its substance are inaccessible, and all information is obtained by indirect geophysical or geochemical methods. Thanks to them, it was possible to determine that, most likely, it is hard, as it is under tremendous pressure from the overlying layers. Approximately 85% of the core consists of iron, 10% of nickel, and the remaining 5% is silicon.
