INTRODUCTION

The structure of the earth is divided into four major components: the crust, the mantle, the outer core, and the inner core. These layers are both physically and chemically different.  Each layer has a unique chemical composition, physical state, and can impact life on Earth's surface.

The Earth has an outer solid layer called the crust, a highly viscous layer called the mantle, a liquid layer that is the outer part of the core, called the outer core, and a solid center called the inner core. This is due to the relative melting points of the different layers (nickel-iron core, silicate crust, and mantle) and the increase in temperature and pressure as depth increases.

There are three chemical layers; the crust, the mantle, and core, and five recognized physical layers; the lithosphere, asthenosphere, mesosphere, outer core, and inner core.

The Earth's geosphere is divided into three chemical sections: The crust, composed almost entirely of light elements, like silicon. The mantle, which is 68% of the Earth's mass. The core, the innermost layer; is composed of very dense elements, such as nickel and iron.

Key concepts of Earth’s structure

The activities in this topic are designed to explore the following key concepts:

• Different layers of the Earth.
• Concept of crust, the mantle, the outer core, and the inner-core.
• Concept of the Earth's geosphere: three chemical and five the physical sections
• Earth's crust is divided into two types: oceanic crust and continental crust.
• Movement of Earth’s crust.
• Earth’s plate movements are responsible for earthquakes and volcanoes.
• Earth’s plate movements are responsible for the creation of mountain ranges.
• Soils on Earth are the result of weathering of rocks.
• Minerals are the building blocks of rocks.
• Earth's mantle is divided into two major rheological layers
• Temperature, Pressure, and Density of the Earth’s Interior.
• Spheres of the Earth’s Structure.
• Earth’s interconnected spheres concept.

Different layers of the Earth

1. Crust Layer

“Crust” describes the outermost shell of a terrestrial planet. Earth's crust is generally divided into older, thicker continental crust and younger, denser oceanic crust. The crust is made of solid rocks and minerals. Together, these solid parts are called the lithosphere. Earth's crust is made up of hard rocks.

            It is the only part of the Earth that humans see. The Earth’s crust is the outermost layer, consisting mainly of the chemical elements silicon and aluminum. The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is significantly denser than the crust.

The temperature of the crust increases with depth, reaching values typically in the range from about 100 °C (212 °F) to 600 °C (1,112 °F) at the boundary with the underlying mantle.

The lithosphere (litho: rock; sphere: layer) is the strong, upper 100 km of the Earth. The lithosphere is the tectonic plate we talk about in plate tectonics. The asthenosphere extends from 100 km depth to 660 km beneath the Earth's surface. Beneath the asthenosphere is the mesosphere, another strong layer.

The crust of Earth is of two distinct types:

1. Oceanic: 5 km (3 mi) to 10 km (6 mi) thick and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro. The oceanic crust is denser than the continental crust.
2. Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite.

Movement of Earth’s crust

          Plate tectonics is the scientific theory explaining the movement of the earth's crust. The movement of these tectonic plates is likely caused by convection currents in the molten rock in Earth's mantle below the crust. Earthquakes and volcanoes are the short-term results of this tectonic movement.

          Earth’s plate movements are responsible for the creation of mountain ranges. At convergent boundaries, plates collide with one another. The collision buckles the edge of one or both plates, creating a mountain range or subducting one of the plates under the other, creating a deep seafloor trench. Convergent plate movement also creates earthquakes and often forms chains of volcanoes

          Soils on Earth are the result of weathering of rocks. Soil is the thin layer of material covering the earth's surface and is formed from the weathering of rocks. It is made up mainly of mineral particles, organic materials, air, water, and living organisms—all of which interact slowly yet constantly.

          Minerals and rocks are the essential building blocks of the geosphere. The crust of the earth is made up of more than 2000 minerals, but out of these, only six are the most abundant and contribute the maximum. These six most abundant minerals are feldspar, quartz, pyroxenes, amphiboles, mica, and olivine.

2. The Mantle Layer

"The mantle" is Earth's second layer. The mantle has two main parts, the upper mantle, and the lower mantle. The upper mantle is attached to the layer above it called the crust. Together the crust and the upper mantle form a fixed shell called the lithosphere, which is broken into sections called tectonic plates.

          The mantle is the mostly-solid bulk of Earth's interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick and makes up a whopping 84% of Earth's total volume. Over millions of years, the mantle cooled.

Earth's mantle is divided into two major rheological layers: the rigid lithosphere comprising the uppermost mantle, and the more ductile asthenosphere, separated by the lithosphere-asthenosphere boundary. Lithosphere underlying ocean crust has a thickness of around 100 km, whereas lithosphere underlying continental crust generally has a thickness of 150–200 km. The lithosphere and overlying crust make up tectonic plates, which move over the asthenosphere. 

3. The Outer Core Layer

            "The outer core" is the 3rd tier of the Earth. It is the lone fluid layer and is mostly made up of metals such as iron and nickel, as well as small measures of additional materials. The outer core is accountable for Earth's magnetic field.

The metallic nickel-iron outer core is liquid because of the high temperature. However, the intense pressure, which increases towards the inner core, dramatically changes the melting point of the nickel-iron, making it solid.

4. The Inner Core Layer

Earth's "Inner Core" is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon's radius. There are no samples of Earth's core accessible for direct measurement, as there are for Earth's mantle.

The inner core and the outer core are made up of similar stuff chemically (both are made mostly of iron, with a little nickel and some other chemical elements) the difference between them is that the outer core is liquid and the inner core is solid.

Temperature, Pressure, and Density of the Earth’s Interior

Temperature

• A rise in temperature with an increase in depth is observed in mines and deep wells.
• This evidence along with molten lava erupted from the earth’s interior supports that the temperature increases towards the center of the earth.
• The different observations show that the rate of increase of temperature is not uniform from the surface towards the earth’s center. It is faster at some places and slower at other places.
• In the beginning, this rate of increase of temperature is at an average rate of 1 0C for every 32m increase in depth.
• While in the upper 100kms, the increase in temperature is at the rate of 120C per km, and in the next 300kms, it is 200C per km. But going further deep, this rate reduces to a mere 100C per km.
• Thus, it is assumed that the rate of increase of temperature beneath the surface is decreasing towards the center (do not confuse rate of increase of temperature with increase of temperature. Temperature is always increasing from the earth’s surface towards the center).
• The temperature at the center is estimated to lie somewhere between 30000C and 50000C, which may be that much higher due to the chemical reactions under high-pressure conditions.
• Even at such a high temperature also, the materials at the center of the earth are in a solid-state because of the heavy pressure of the overlying materials.

Pressure

• Just like the temperature, the pressure is also increasing from the surface towards the center of the earth.
• It is due to the huge weight of the overlying materials like rocks.
• It is estimated that in the deeper portions, the pressure is tremendously high which will be nearly 3 to 4 million times more than the pressure of the atmosphere at sea level.
• At high temperatures, the materials beneath will melt towards the center part of the earth but due to heavy pressure, these molten materials acquire the properties of a solid and are probably in a plastic state.

Density

• Due to the increase in pressure and presence of heavier materials like Nickel and Iron towards the center, the density of the earth’s layers also gets on increasing towards the center.
• The average density of the layers gets on increasing from crust to core and it is nearly 14.5g/cm3 at the very center.

Spheres of the Earth’s Structure

           Everything in Earth's system can be placed into one of four major subsystems: land, water, living things, or air. These four subsystems are called "spheres." Specifically, they are the "lithosphere" (land), "hydrosphere" (water), "biosphere" (living things), and "atmosphere" (air).

          Earth is also defining interconnected spheres - Cryosphere, Hydrosphere, Atmosphere, Biosphere, Lithosphere, and Magnetosphere.

• Lithosphere: The lithosphere is the outer solid shell of the Earth. The lithosphere includes the crust and, below, the uppermost layer of the mantle; it floats on the weaker asthenosphere. There are two types of lithospheres: Oceanic lithosphere, which is associated with Oceanic crust The lithosphere consists of solid rock, soil, and minerals. All the rocks on Earth make up the rigid sphere of Earth known as the lithosphere. 

• Hydrosphere: The hydrosphere consists of water in all its forms. The hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet's hydrosphere can be liquid, vapor, or ice. On Earth, liquid water exists on the surface in the form of oceans, lakes, and rivers.

• Atmosphere: The atmosphere is the layer of gases around the Earth. The sphere in the atmosphere is the troposphere, stratosphere, mesosphere, and thermosphere. A further region at about 500 km above the Earth's surface is called the exosphere.

• Cryosphere: The cryosphere is the frozen water part of the Earth system. One part of the cryosphere is ice that is found in water. This includes frozen parts of the ocean, such as waters surrounding Antarctica and the Arctic. There are places on Earth that are so cold that water is frozen solid.

• Biosphere: The biosphere is made up of the parts of Earth where life exists-all ecosystems. The biosphere extends from the deepest root systems of trees to the dark environments of ocean trenches, to lush rain forests, high mountaintops, and transition zones like this one, where ocean and terrestrial ecosystems meet.

• Magnetosphere: A magnetosphere is a region around a planet dominated by the planet's magnetic field. The magnetosphere shields our home planet from solar and cosmic particle radiation, as well as erosion of the atmosphere by the solar wind - the constant flow of charged particles streaming off the sun.

• Geosphere: The geosphere is the whole outer shell of Earth. These are all the rocks and sand particles from dry land to those found at the bottom of the oceans. They also include the mountains, minerals, lava, and molten magma from beneath the earth's crust. The geosphere undergoes infinite processes constantly and that, in turn, modifies other spheres.

Conclusion

          Earth is made of four layers, the crust, mantle, and outer core, and inner core. Inside and around Earth there are five spheres, the Geosphere (Lithosphere), the Atmosphere, the Hydrosphere, the Cryosphere, and the Biosphere. These spheres all interact to make life what it is here on Earth. It is the ground we walk on, the air we breathe, the water we drink. the cold places we live and all the living creatures here on Earth.