Conditions Of The Center Of The Earth Recreated In The Laboratory For The First Time
For the first time, Japanese scientists managed to obtain the pressures and temperatures characteristic of the Earth's outer core using a cell with diamond anvils in a laboratory experiment, and also check what its composition would be. The results are published in the journal Physical Review Letters.
Primary data on the state of the earth's inner shells are obtained by geophysicists from the results of seismic observations. Large earthquakes cause seismic waves that propagate in the body of the planet, and by the nature of their passage, changes in speed and refraction, scientists judge the deep structures and boundaries of the Earth's layers.
From the results of seismic observations, it is known that in the center of the Earth there is a solid core surrounded by a less dense, partially molten shell — the outer core. Scientists suggest that this shell is composed of molten iron, possibly with admixtures of some other elements.
Computer modeling and physical calculations allow us to assume what conditions should be in this zone — pressure, and temperature. But scientists have always wanted to test this data experimentally. It is clear that it is impossible to drill a well to the core of the Earth and lower the probe there, so it was only about experiments on devices.
Japanese scientists from the University of Tokyo decided to model the conditions of the earth's core using a structure called a cell with diamond anvils. Physically, it consists of two conical diamonds, through the sharp ends of which compressive forces are transmitted to work sites with a diameter of less than a millimeter. Due to the exceptional hardness and strength of the diamond, pressures of several million atmospheres can be achieved in this way over a huge temperature range, and the transparency of the diamonds allows the sample to be studied through them using a lot of methods.
The authors modified the diamond anvil in a certain way, which allowed them to achieve for the first time in a laboratory experiment the pressures and temperatures characteristic of the outer core while making x-ray measurements. Another difficulty lay in the fact that in a diamond anvil should have not pinched between the solid material and the liquid iron. It is more difficult to measure the density of a liquid sample than a solid one since it takes longer to do so. But thanks to a unique experimental setup that the authors created over twenty years, they were able to collect the necessary data.
"It is not easy to recreate the conditions of the Earth's center here on the surface," the first author of the study, Yasuhiro Kuwayama, said in a University press release. We used a diamond anvil to compress a sample of liquid iron subjected to high heat. But in order to create the conditions, we had to maintain them long enough to make measurements. This was a real problem."
Researchers have successfully determined the density of liquid iron and the speed of sound propagation through it at extremely high pressures. To do this, they used a high-focus x-ray source of the SPring-8 synchrotron complex with the world's highest energy, located in Hyogo Prefecture, Japan.
The results confirmed that liquid iron has about 8 percent more density than the molten outer core, which means that the latter contains other, lighter elements besides iron, which are not currently identified.
"We found that the density of liquid iron, such as in the outer core, is about 10 tons per cubic meter at a pressure of 116 gigapascals, and a temperature of 4350 Kelvins, Kuwayama explained. For reference, the typical room temperature is about 273 Kelvins. So this sample is 16 times hotter than your room and 10 times denser than water."
The authors hope that their results will help to reveal the secrets of the deep structure of the Earth and will be useful in building models of other planets.