What are the layers of the Earth? Earth has four layers: 1) Curst 2) Mantle 3) Outer Core and 4) Inner Core.
Planet Earth is a rocky planet with the highest density of the Solar System. Its internal structure consists of several layers with different composition and with different mechanical properties.
Starting with the surface, the crust is formed by solid rock and represents about 1% of the earth’s mass. It is followed by the mantle, which contains 68% of the planet’s mass, and finally the core, which is further divided into two parts Inner layer and Outer layer, basically composed of metallic iron.
Internal Structure of the Earth:
Curst: 0-35 km deep, being able to reach 70 km locally.
Mantle: 35-2890 km (upper mantle 35-660 km, lower mantle 660-2890 km).
Core: 2890-6371 km (outer core 2890-5150 km, inner core 5150-6371).
These layers have been determined indirectly by studying the behavior of different types of seismic waves when moving from one layer to another (speed changes, refraction, etc.)
The outer layer of the Earth is the crust. It is composed of rock and is the coldest and thinnest layer compared to the others, in fact, it is a very thin layer in relation to the radius of the planet, it only contains 1% of the earth’s mass.
Within the crust, two very different types are distinguished, the continental crust and the oceanic crust, each with its own physical and chemical characteristics.
The oceanic crust is composed of solidified magma that erupts in the ocean ridges and underwater volcanoes and creates basaltic lava and intrusive igneous rocks like gabbro.
The sediments that cover the oceanic crust are sludge and calcareous shells of small marine organisms, for example, diatomaceous earth. Near the coasts, the sediment layer is much thicker, as greater amounts of sediment arrive from the continents through the rivers and the wind.
The continental crust, on the other hand, is composed of many types of igneous, metamorphic and sedimentary rocks. However, granite is the most abundant rock, a rock with a density much lower than the rocks of the oceanic crust.
Due to this lower density and greater thickness, the continental crust rises much higher above the mantle than the oceanic crust.
The lithosphere is defined by mechanical properties, not by composition, and not only includes curst but reaches a small part of the upper mantle.
The lithosphere is the outermost rigid layer of the planet and reaches up to approximately 100 km deep, while the crust remains on average at 35 km.
Because the lithosphere is rigid, when the stresses of tectonic movements break it, earthquakes occur.
The mantle is located below the earth’s crust and reaches 2890 km deep, being the largest layer on the planet. It is believed to be composed mainly of igneous rocks rich in olivine group minerals (silicates rich in iron and magnesium).
The two most important characteristics of the mantle are that it is formed by solid rocks and that it is very hot. The temperature increases with depth (932 to 1,652 degrees Fahrenheit, 500 to 900 degrees Celsius), being cooler in the upper mantle and reaching the maximum temperature in the area of the lower mantle in contact with the core.
This temperature increase with depth is known as a geothermal gradient. The geothermal gradient is responsible for the mantle rocks also having a different behavior at different depths, which allows us to divide the mantle into two parts:
Upper mantle: the rocks of the upper mantle (35-660 km) are cooler and more fragile than those of the lower mantle.
Lower mantle: it goes from 660 km deep to reach the core at 2890 km deep. The rocks of the lower mantle are much hotter, so much that they become soft and ductile, although they are still in a solid-state.
Heat can be transmitted in two ways: conduction and convection. The conduction is produced by a collision between the atoms of matter, which transfers energy but not mass. For its part, thermal convection involves the transfer of mass from warmer areas to colder areas until an eventual equilibrium is reached.
The two types of heat transfer occur in the mantle. Convection is similar to that produced in a pot of boiling water, although much slower in time. As the core heats the lower mantle, the rocks in this area become less dense and tend to rise. The rising material thus creates convection current.
When the hot material reaches the surface, it disperses horizontally, cools and becomes denser until it begins to descend again, closing the convection current.
These currents of convection and movement of the mantle are responsible for the majority of tectonic phenomena on the planet.
The core is located at a depth of 2890 km and reaches 6371 km, where the center of the planet would be. All the data indicate that it is mainly composed of iron together with 5-10% nickel and smaller amounts of other light elements such as sulfur and oxygen.
The core is the internal source of heat and is divided into two zones:
Outer core: it is in a liquid state since the temperature in this area is sufficient to melt the iron and nickel alloy that makes up the core. The outer core reaches between 7,200 and 9,000 degrees Fahrenheit (4,000 and 5,000 degrees Celsius) and is estimated to be 1,430 miles (2,300 km) thick.
Inner core: The inner core is the hottest part of our planet, at temperatures between 9,000 and 13,000 degrees Fahrenheit (5,000 and 7,000 degrees Celsius). Despite the high temperatures, the inner core is in a solid-state due to the high pressures it is subjected to.
Iron, like the rest of the metals, is magnetic. The convection and rotation of the outer core is the source of the Earth’s magnetic field.