Internal structure of the earth

Internal structure of the Earth

The internal structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and geological properties. The Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer cover that is much less viscous than the mantle and a solid inner core.

Internal structure of the Earth

Inner structure of the Earth with its components, depth and temperature

Composition of the internal layers of the Earth

The Earth's interior consists of different layers that vary in composition and density. These layers interact in complex ways, creating the dynamic processes that shape the Earth's surface. The interior layers can be described based on mechanical properties and chemical composition. Below is an explanation of these layers and their characteristics.

a. The Crust

The Earth's crust is the outermost layer, ranging from 5 to 70 kilometers (3 to 44 miles) deep. It is the thinnest layer of the Earth and is divided into two main types:

• Continental Crust (SIAL): This is the thicker, less dense crust that forms the continents. It is composed primarily of silicate and aluminum (SIAL). The rocks in the continental crust are primarily felsic, such as granite and quartz, which makes it less dense than oceanic crust.
• Oceanic Crust (SIMA): This crust is thinner, denser, and composed mainly of silicate and magnesium (SIMA). The oceanic crust is predominantly made up of mafic rocks like basalt, which have lower amounts of silica and more iron and magnesium.

The boundary between the Earth's crust and the mantle is known as the Mohorovicic Discontinuity or Moho, discovered by Andrija Mohorovicic in 1909. This discontinuity marks a change in the speed of seismic waves, indicating a change in the composition of the rocks.

b. The Mantle

The mantle lies beneath the crust and extends to a depth of about 2,890 kilometers (1,790 miles). It is composed primarily of iron and magnesium and is the thickest layer of the Earth. The mantle is divided into:

• Upper Mantle: This is the region closest to the crust, and it includes the asthenosphere, a semi-molten layer responsible for plate tectonics and isostatic adjustment. It extends about 400 kilometers deep.
• Lower Mantle: This region is beneath the asthenosphere and extends down to the core-mantle boundary. It is solid but experiences intense heat and pressure.

The mantle is also home to a boundary called the Gutenberg Discontinuity, which separates the mantle from the outer core. This layer is where the pressure and temperature increase dramatically, reaching around 3,700°C at its deepest point.

c. The Core

The core is the innermost layer of the Earth, consisting of two parts:

• Outer Core: This layer is molten and extends from about 2,890 kilometers to 5,150 kilometers below the surface. It is primarily made of iron and nickel and is responsible for generating the Earth's magnetic field. The liquid state allows the outer core to produce convection currents, which contribute to Earth's magnetism.
• Inner Core: The inner core is solid, composed mainly of iron and nickel, and extends from about 5,150 kilometers to the Earth's center at approximately 6,371 kilometers. Despite the extreme heat, the pressure is so high that the inner core remains solid. It has an estimated temperature of around 6,000°C, even hotter than the surface of the Sun.

The boundary between the outer and inner core is known as the Lehmann Discontinuity, discovered by Inge Lehmann in 1936.

d. Earth's Gravity

Gravity is the force that pulls objects towards the Earth's center. This force is responsible for giving weight to objects and controlling the movement of the oceans, resulting in tides. The strength of Earth's gravity is not uniform across the planet, and it is influenced by:

• Distance from Earth's center: Gravity is stronger at sea level and weaker at higher altitudes.
• Earth's rotation: The rotation causes a slight outward force at the equator, which reduces the effective force of gravity there.
• Geological variations: Mountains, underground caverns, and variations in Earth's density can create local anomalies in gravitational strength.

Gravity is essential for the structure of the Earth and the universe, keeping everything from planets to satellites in orbit. It is also what makes man-made satellites possible and enables life on Earth by holding the atmosphere and oceans in place.