EARTH STRUCTURE
INTRODUCTION
Earth is the third planet in the solar system after Mercury and Venus. It is about 150 million kilometers from the Sun and lies in the "habitable zone," which allows liquid water and life to exist. Earth is the only planet with a nitrogen- and oxygen-rich atmosphere and a magnetic field. Earth makes two rotations: one revolution around the Sun and one rotation around its own axis.
THE STRUCTURE
The Earth is made up of four main layers: the crust, mantle, outer core, and inner core. Scientists discovered these layers by studying seismic waves, since it is impossible to reach such great depths to collect samples directly. The Earth has an almost spherical shape, slightly flattened at the poles, with an average radius of about 6,360 km. Geological studies estimate that the Earth is about 4.543 billion years old. Although some incorrect theories claim that the Earth is flat or hollow, science explains that its internal structure is composed of different layers.
Earth's crust
The earth's crust is the outermost layer of the Earth and is the one on which living beings live and the main geological phenomena develop. It has a variable thickness: under the oceans it measures about 5–10 km, while under the continents it can reach 30–70 km. There are two main types of crust: the oceanic crust, thinner and denser, composed mainly of basaltic rocks, and the continental crust, thicker and less dense, mainly composed of granitic rocks. The crust is not a single block but is divided into large tectonic plates that move slowly over the mantle. The movements of these plates cause phenomena such as earthquakes, volcanoes and the formation of mountain chains. Together with the upper part of the mantle, the crust forms the lithosphere, which constitutes the outermost rigid structure of the planet.
PLATE TECTONICS
Plate tectonics is a theory that allows us to explain many of the phenomena affecting our planet, such as earthquakes, volcanoes and orogenies. Plate tectonics is a theory according to which the surface portion of our planet, the lithosphere, is divided into plates. These would be nothing more than large portions of the earth's crust that continually move next to each other, like in a large puzzle. In addition to the twenty main plates, smaller micro-plates must be added. This theory, still in use today, was developed by Alfred Wegener during the twentieth century and is based on the idea that the heat inside our planet, through the so-called convective motions, allows the plates to move even if there are alternative theories to this model. This theory has managed to bring together many phenomena that until recently seemed disconnected from each other, such as earthquakes and volcanoes or orogeny and expansion of the oceans: for this reason it is defined as "theory unifying."
MANTLE
The mantle is the thickest layer of the Earth and lies between the crust and the core. It extends from about 35 km below the Earth's surface to a depth of around 2,900 km. The mantle is mainly made of solid rock rich in minerals such as silicon, oxygen, magnesium, and iron. Although it is mostly solid, the rocks in the mantle can slowly flow over long periods of time because of the high temperature and pressure.
The mantle is divided into two main parts: the upper mantle and the lower mantle. The upper mantle includes a softer region called the asthenosphere, where rocks are partially molten and can move slowly. This movement is responsible for the motion of tectonic plates on the Earth's surface.
Heat from the Earth's core causes convection currents in the mantle. These currents slowly move hot material upward and cooler material downward, driving the movement of continents, earthquakes, and volcanic activity. The mantle plays a crucial role in shaping the Earth's surface and geological processes.
Outer core
The outer core is a layer of the Earth located between the mantle and the inner core. It lies at depths between about 2,900 km and 5,100 km below the Earth's surface and is about 2,200 km thick. Unlike the inner core, the outer core is in a liquid state and is composed mainly of molten iron and nickel. Temperatures in this area are extremely high and can reach around 4,000–5,000 °C. The movement of liquid metals within the outer core generates the Earth's magnetic field, which protects the planet from solar radiation and particles from space. This layer therefore has a fundamental role in maintaining the conditions that allow life on Earth.
INNER CORE
The inner core is the deepest and hottest layer of the Earth. It is located at the center of the planet and begins at a depth of about 5,150 km, extending to the Earth's center at around 6,371 km. Despite the extremely high temperatures, estimated to be similar to the surface of the Sun, the inner core is solid because of the immense pressure from the layers above it.
The inner core is mainly composed of iron and nickel. Scientists study it indirectly by analyzing how seismic waves from earthquakes travel through the Earth. These waves change speed and direction when they pass through different materials, which helps researchers understand the structure of the inner core.
The inner core plays an important role in Earth's magnetic field. Together with the movement of liquid metal in the outer core, it helps generate and maintain the magnetic field that protects the planet from harmful solar radiation.
EARTH STRUCTURE
Andrea Zottoli
Created on February 25, 2026
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Transcript
EARTH STRUCTURE
INTRODUCTION
Earth is the third planet in the solar system after Mercury and Venus. It is about 150 million kilometers from the Sun and lies in the "habitable zone," which allows liquid water and life to exist. Earth is the only planet with a nitrogen- and oxygen-rich atmosphere and a magnetic field. Earth makes two rotations: one revolution around the Sun and one rotation around its own axis.
THE STRUCTURE
The Earth is made up of four main layers: the crust, mantle, outer core, and inner core. Scientists discovered these layers by studying seismic waves, since it is impossible to reach such great depths to collect samples directly. The Earth has an almost spherical shape, slightly flattened at the poles, with an average radius of about 6,360 km. Geological studies estimate that the Earth is about 4.543 billion years old. Although some incorrect theories claim that the Earth is flat or hollow, science explains that its internal structure is composed of different layers.
Earth's crust
The earth's crust is the outermost layer of the Earth and is the one on which living beings live and the main geological phenomena develop. It has a variable thickness: under the oceans it measures about 5–10 km, while under the continents it can reach 30–70 km. There are two main types of crust: the oceanic crust, thinner and denser, composed mainly of basaltic rocks, and the continental crust, thicker and less dense, mainly composed of granitic rocks. The crust is not a single block but is divided into large tectonic plates that move slowly over the mantle. The movements of these plates cause phenomena such as earthquakes, volcanoes and the formation of mountain chains. Together with the upper part of the mantle, the crust forms the lithosphere, which constitutes the outermost rigid structure of the planet.
PLATE TECTONICS
Plate tectonics is a theory that allows us to explain many of the phenomena affecting our planet, such as earthquakes, volcanoes and orogenies. Plate tectonics is a theory according to which the surface portion of our planet, the lithosphere, is divided into plates. These would be nothing more than large portions of the earth's crust that continually move next to each other, like in a large puzzle. In addition to the twenty main plates, smaller micro-plates must be added. This theory, still in use today, was developed by Alfred Wegener during the twentieth century and is based on the idea that the heat inside our planet, through the so-called convective motions, allows the plates to move even if there are alternative theories to this model. This theory has managed to bring together many phenomena that until recently seemed disconnected from each other, such as earthquakes and volcanoes or orogeny and expansion of the oceans: for this reason it is defined as "theory unifying."
MANTLE
The mantle is the thickest layer of the Earth and lies between the crust and the core. It extends from about 35 km below the Earth's surface to a depth of around 2,900 km. The mantle is mainly made of solid rock rich in minerals such as silicon, oxygen, magnesium, and iron. Although it is mostly solid, the rocks in the mantle can slowly flow over long periods of time because of the high temperature and pressure. The mantle is divided into two main parts: the upper mantle and the lower mantle. The upper mantle includes a softer region called the asthenosphere, where rocks are partially molten and can move slowly. This movement is responsible for the motion of tectonic plates on the Earth's surface. Heat from the Earth's core causes convection currents in the mantle. These currents slowly move hot material upward and cooler material downward, driving the movement of continents, earthquakes, and volcanic activity. The mantle plays a crucial role in shaping the Earth's surface and geological processes.
Outer core
The outer core is a layer of the Earth located between the mantle and the inner core. It lies at depths between about 2,900 km and 5,100 km below the Earth's surface and is about 2,200 km thick. Unlike the inner core, the outer core is in a liquid state and is composed mainly of molten iron and nickel. Temperatures in this area are extremely high and can reach around 4,000–5,000 °C. The movement of liquid metals within the outer core generates the Earth's magnetic field, which protects the planet from solar radiation and particles from space. This layer therefore has a fundamental role in maintaining the conditions that allow life on Earth.
INNER CORE
The inner core is the deepest and hottest layer of the Earth. It is located at the center of the planet and begins at a depth of about 5,150 km, extending to the Earth's center at around 6,371 km. Despite the extremely high temperatures, estimated to be similar to the surface of the Sun, the inner core is solid because of the immense pressure from the layers above it. The inner core is mainly composed of iron and nickel. Scientists study it indirectly by analyzing how seismic waves from earthquakes travel through the Earth. These waves change speed and direction when they pass through different materials, which helps researchers understand the structure of the inner core. The inner core plays an important role in Earth's magnetic field. Together with the movement of liquid metal in the outer core, it helps generate and maintain the magnetic field that protects the planet from harmful solar radiation.