The Earth consists of three concentric spheres: the earth’s crust, earth’s mantle a the earth’s core. If we wanted to be more consistent, then we can divide these parts into five layers – the earth’s crust, upper coat, lower shell, semi-fluid outer core a solid inner core. But according to seismologists from the Australian National University, there is evidence of the existence of another layer – the innermost solid core (subcore) with a diameter of about 640 kilometers. Research Thanh-Son Phama a Hrvoje Tkalčić published prestigious scientific journal Nature Communications.
Similar to the solid inner core, this subcore should also be made of a mixture of nickel and iron. According to the scientists, the transition between the solid core and the subcore is not sharp and is due only to the different crystal structure. It was this feature that contributed to the discovery of its existence – according to the researchers, the different structure has an effect on the speed of the passing shock waves generated during earthquakes.
Following the waves
The existence of a solid inner core surrounded by a liquid envelope was first described in 1936 by a Danish seismologist Inge Lehmann. This innermost part of the Earth is located approximately 5,100 kilometers below the surface, its size is around 1,300 kilometers and it makes up less than 1% of the Earth’s volume.
The great distance, and especially the extreme conditions prevailing in the center of the Earth, understandably make any direct research of it impossible. One of the few ways to study the Earth’s core is to measure the tiny differences in seismic waves that occur in earthquakes and nuclear explosions. Measurements of seismic waves created during earthquakes have shown that their speed changes depending on the angle of entry of these waves into the earth’s core. According to the scientists, this indicates a different anisotropy of the core.
The theory of the Earth’s inner subcore is not entirely new – it first appeared about 20 years ago, new findings by seismologists from the Australian National University in Canberra are supposed to confirm this hypothesis. According to geophysicist Johna Tarduna from the University of Rochester, who was not involved in the new research, the (possible) existence of the sub-nucleus raises questions about its origin. While the authors of the study believe that this subcore may be the result of a “significant global event from the past” that triggered a change in the Earth’s inner core, Tarduno offers a different explanation – according to the British geophysicist, the formation of the subcore could be related to a change in plate tectonics hundreds of millions of years ago.
TIP: The path to the core: What are the conditions in the very center of the Earth?
In any case, these are important questions, as understanding the origin and formation of the core’s inner layers can help us better understand how the Earth’s magnetic field was formed – and thus how life can thrive on Earth (and possibly other planets). The magnetic field provides us with a very important part of the defense against charged particles from space (mainly from the Sun), which would otherwise have a destructive effect on all living organisms.
