Internal Structure of the Earth - Delhi Police Constable PDF Download

Introduction

Gaining direct insight into the Earth's interior is a daunting task, given its colossal size and ever-changing composition. Human exploration can only venture a few kilometers below the surface due to rapidly increasing temperatures. However, through both direct and indirect sources, scientists have managed to gain a fair understanding of the Earth's hidden domains.

Direct Sources:

• Rocks from mining areas
• Volcanic eruptions

Indirect Sources:

• Analyzing temperature and pressure changes from the surface towards the interior
• Studying meteors composed of similar materials as Earth
• Gravitation variations from poles to the equator
• Gravity anomaly, providing insights into materials in the Earth's interior
• Magnetic sources
• Seismic waves and shadow zones, revealing information about interior materials

Structure of the Earth's Interior

The Earth's interior is divided into three distinct layers, each with its unique properties and significance.

Crust: The outermost layer, approximately 8-40 kilometers thick, constitutes merely 1% of the Earth's volume and 0.5% of its mass. It is a brittle layer primarily composed of Silica (Si) and Aluminium (Al), often referred to as SIAL. The oceanic crust (about 5 kilometers thick) differs from the continental crust (about 30 kilometers thick). The average density of crust materials is 3g/cm³. The boundary between the hydrosphere and the crust is known as the Conrad Discontinuity.

Mantle: Beyond the crust lies the mantle, extending approximately 2900 kilometers in thickness. This voluminous layer makes up 84% of the Earth's volume and 67% of its mass. The major elements in the mantle are Silicon and Magnesium, hence termed as SIMA. Its density ranges from 3.3 to 5.4g/cm³. The lithosphere, comprising the uppermost solid part of the mantle and the entire crust, is separated from the underlying asthenosphere by the Repetti Discontinuity. The asthenosphere, highly viscous and ductile, plays a vital role in plate tectonics.

Core: The core, surrounding the Earth's center, is separated from the mantle by Guttenberg's Discontinuity. Comprising mainly iron (Fe) and nickel (Ni), it is called NIFE. Although the core represents only 15% of Earth's volume, it accounts for 32.5% of its mass. The core is the densest layer, with a density ranging from 9.5 to 14.5g/cm³. It consists of an inner solid core and an outer liquid or semi-liquid core. The Lehmann Discontinuity marks the boundary between these two sub-layers. The term "Barysphere" is sometimes used to refer to the core or the entire Earth's interior.

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

Exploring the temperature, pressure, and density variations within the Earth's interior provides invaluable insights into its dynamic nature.

Temperature:

As we delve deeper into mines and wells, we observe a rise in temperature with increasing depth. Molten lava eruptions also indicate increasing temperatures towards the Earth's center. The rate of temperature increase is not uniform, with variations at different depths. Nevertheless, the general trend shows an average rate of 10°C per 32 meters at the beginning, 120°C per kilometer in the upper 100 kilometers, and 200°C per kilometer in the following 300 kilometers. At greater depths, the rate reduces to 100°C per kilometer. The estimated temperature at the Earth's center ranges from 3000°C to 5000°C and could be even higher due to chemical reactions under high-pressure conditions.

Pressure:

Like temperature, pressure increases as we descend towards the Earth's center. This immense pressure results from the weight of overlying materials, such as rocks. In deeper portions, pressure becomes astronomically high—around 3 to 4 million times more than atmospheric pressure at sea level. Despite high temperatures, the materials beneath the surface remain solid due to the pressure exerted by the overlying layers.

Density:

Density increases towards the Earth's center due to the presence of heavier elements like Nickel and Iron. From crust to core, the average density rises, reaching nearly 14.5g/cm³ at the center of the Earth.