The Structure and Composition of the Earth

The Earth has three main layers:

  • Crust
  • Mantle
  • Core

The image portrays a visual representation of the Earth's internal structure, depicted in two distinct sections. On the left, a cross-sectional view of the Earth is displayed, revealing its multicoloured layers. The outermost layer, coloured in shades of blue and green, represents the crust, which encompasses the oceans and continents. Below the crust, a broad, orange layer signifies the mantle. Deeper within, a reddish-orange layer depicts the outer core, followed by a bright yellow section that symbolises the inner core. Each of these layers is distinctly labelled.On the right side of the image, a segmented, vertical illustration provides a more simplified view of the Earth's layers, emphasising the depth of each layer. From the surface downwards, labels indicate "Sea Level", followed by the crust, which is depicted up to a depth of 100 km. The mantle extends further down, reaching a depth of 2,900 km. The outer core continues until 5,190 km, and the inner core extends to the planet's centre at 6,371 km. The depths are marked with specific measurements, aiding in visualising the relative thickness of each layer.

Starting from the outermost layer, the Earth is composed of the crust, followed by the mantle, and finally the core.

Earth’s Layers

The crust

The Earth’s crust is the thinnest of the three layers, and it is the solid surface where we stand and live. This rocky layer is divided into large pieces called tectonic plates. The movement of these tectonic plates is responsible for many geological activities, such as earthquakes, volcanic eruptions, and the formation of mountain ranges.

However, the thickness of the crust varies depending on the location. In some areas, it is very thick, while in other areas it is very thin. We live on the thicker areas of crust, known as continental crust, which are higher ground. Oceans lie above a thinner type of crust, known as oceanic crust, which is generally submerged in water and not as thick as continental crust. The thinner areas of the crust can cause problems like earthquakes.

The two types of crust are very different from each other and are made up of different minerals and rocks. Continental crust is usually thicker and less dense than oceanic crust. On average, continental crust is around 35 to 40 km thick, while oceanic crust is typically around 5 to 10 km thick.

Also, continental crust is generally older than oceanic crust. Some areas of continental crust are more than 4 billion years old, while most oceanic crust is 200 million years old or younger.

The mantle

The Earth’s mantle is the thickest of the three layers. It is made mostly of solid rock and behaves like a solid; however, it can also flow beneath the crust. Due to convection currents, hot rock slowly rises while cooler rock falls.

The core

The centre of the Earth is called the core, which is divided into the inner core and the outer core.

  • The outer core is made from liquid iron and nickel
  • The inner core is solid

Both iron and nickel are magnetic, contributing to the Earth’s magnetic field.

Elements Larger than Iron

In the periodic table below, iron (Fe) is circled.

The image depicts the Periodic Table of Elements, a structured arrangement of chemical elements, organised based on their atomic number, electron configuration, and recurring chemical properties. Each element's tile includes its atomic number, chemical symbol, and relative atomic mass. Elements are colour-coded to represent their respective categories.Starting from the left, the elements are grouped into: alkaline metals (bright green), alkaline earth metals (light green), transition metals (yellow), basic metals (peach), metalloids (grey), carbon and other non-metals (aqua), halogens (blue), and noble gases (deep blue). The table also highlights the Lanthanoids and Actinoids, two series of elements separated at the bottom in light green and mustard yellow respectively.A magnified example at the top-left corner displays the structure of an element's tile, using Hydrogen (H) as the representative: atomic number is shown above the chemical symbol, followed by the element's name and relative atomic mass. Notably, the element Iron (Fe) in the central section of the table is encircled for emphasis.

While iron is a common element on Earth, we have also discovered elements that are heavier than iron. This suggests that Earth was formed from the explosion of a supernova.

A supernova is an exploding massive star that disperses heavy elements like iron, as well as elements heavier than iron, into space. This eventually formed our planet. Elements heavier than iron only form during supernova explosions.

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