In the geosphere of the planet Earth several layers are distinguished depending on the composition. The three main layers are the crust, mantle and core. The crust is the outermost layer made up of solid rock and a thickness that can vary from 11 km in mid-ocean ridges to 70 km in the highest mountain ranges, such as the Himalayas or the Andes.
Next is the mantle, made up of siliceous-type rocks with a greater amount of iron and magnesium than the rocks of the crust. The core starts at approximate depth of 2890 km and spreads up to 6371 km where the center of the Earth would be. The total radius of the core is about 3,500 km, somewhat larger than the radius of Mars.
Core composition and structure
The depth of the Earth’s core has been measured with different techniques, especially with the study of the seismic wave propagation. Every time an earthquake occurs, the vibrations produced spread throughout the planet in the form of mechanical waves, similar to the waves that propagate sound.
Two types of waves are produced in earthquakes, primary and secondary, and thanks to them it was possible to see that the core consists of two layers, the outer core and the inner core. Secondary waves are only transmitted through solid material and are lost to a depth of about 3000 km, evidence that the outer core is liquid. Primary waves, on the other hand, can propagate through a solid medium and their study shows that The inner core is solid:
- External nucleus: from 2,890 km to 5,150 km deep. Liquid or semi-solid state.
- inner core: from 5,150 km to 6,371 km deep. Solid state.
Composed mainly of heavy elements, such as iron and nickel, the core contains 60% of the entire mass of the Earth and is very dense. In fact, the average density of the Earth is 5515 kg/m3 but the average density of the crust is only 3000 kg/m3.
At the beginning of the formation of the Earth, about 4.5 billion years ago, the denser and heavier materials melted by high temperatures would have sunk towards the center to form the core. The main component of the nucleus is the iron (80%) beside nickel and lesser amounts of other elements.
The lighter elements remained in the crust and mantle. Other heavy elements, such as lead or uranium, are scarce in the core and in the Earth in general, and remained in upper layers together with other elements.
The solid inner core is composed almost entirely of iron and some nickel. Some theories even suggest that to explain the behavior of seismic waves, the inner core would have a atomic structure similar to a single iron crystal. A large iron crystal with a radius of 1,200 km. It is also believed that it could be enriched with elements with an atomic number greater than 55, such as gold, mercury and uranium.
The outer core is a semi-solid shell that surrounds the inner core and is made up of a mixture of iron, which would be the most abundant element, nickel, and other elements. The moving outer core, caused by the Earth’s spin, would be responsible for generating the Earth’s magnetic field, since the temperature of the inner core (about 6000 ºC) would be too high to maintain a stable magnetic field.
This magnetic field protects terrestrial life from the most harmful solar radiation, making possible its existence as we know it, so the composition and structure of the planet’s core has a very prominent role in our own existence and evolution.