One of the basic principles of geology is that the Earth is made up of four layers: the crust, the mantle, the outer core and the inner core, although a recent study by the Australian National University suggested that the Earth actually has a fifth layer other than these four, which has been under our feet all along. This layer would be found within the inner core of the Earth.
Journey to the Center of the Earth
The further we move toward the center of the planet, the more intense the heat and pressure become . Fortunately, for those of us who live in the crust (the outermost layer, where all life lives), the temperature is relatively constant and pleasant. This area constitutes only 1% of the total mass of the Earth, as a curiosity.
The central point of the Earth, which formed in the first 200 of our planet’s 4.6 billion year history , is more than 6,000 km deep. It is made up of two main parts: the outer shell, made of a liquid iron alloy, and, in contrast, the inner core is made of solid iron alloy.
The inner core has an estimated radius of 1,220 km, while the outer core extends further to a radius of about 3,400 km.
a hellish environment
The temperature in the inner core of our planet is approximately 5,200° Celsius , which almost coincides with the surface temperature of the Sun, which is 5,505°C; although there are areas of our star that reach more than 15 million degrees Celsius , of course. Its temperature varies enormously, but the core, where nuclear fusion takes place, is where the pressure and temperature are so high that they can reach so many millions of degrees Celsius. The pressure at the center of the Earth is almost 3.6 million atmospheres (atm). It is approximately 9 million times the atmospheric pressure that humans experience at sea level on the Earth’s surface.
As a curiosity, iron melts at 1535 ºC (when it is at atmospheric pressure), water boils at 100 ºC and human skin supports moderately well up to 55 ºC, when dehydration begins. It is the maximum temperature that human beings can withstand.
Or not so much?
A recent study concluded that the Earth’s core has been cooling since the planet formed about 4.5 billion years ago, when the entire surface was covered by oceans of magma. Scientific understanding of how quickly this cooling occurs suggests that the process is proceeding much faster than scientists previously thought. A finding that adds to a body of research supporting the idea that radiation plays a larger role in extracting heat from the Earth’s core than previously assumed.
And how do scientists measure the temperature of the core?
By indirect deduction (given the enormous distance it is under our feet). They can’t dig deep enough to use a thermometer to measure temperature, so various techniques are used, including studying seismic waves or how iron melts when subjected to extremely high pressures. Iron is unique in that it is the only element that matches well with the seismic characteristics present in the earth’s core.
By recreating these conditions in the laboratory using elemental iron, scientists can make a correct calculation and measurement of core temperature. Experiments done so far have provided reliable temperature estimates for the different layers of the Earth, not just the core.
Referencia: Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm J. Stephenson, H Tkalčić, M. Sambridge First published: 07 December 2020 https://doi.org/10.1029/2020JB020545
Motohiko Murakami, Alexander F. Goncharov, Nobuyoshi Miyajima, Daisuke Yamazaki, Nicholas Holtgrewe, Radiative thermal conductivity of single-crystal bridgmanite at the core-mantle boundary with implications for thermal evolution of the Earth, Earth and Planetary Science Letters, Volume 578, 2022, 117329, ISSN 0012-821X, DOI: https://doi.org/10.1016/j.epsl.2021.117329.
