The core of our planet is iron. But now scientists are getting better at understanding what else is spinning in a whirlpool in the center of the Earth.
The heartbeat of our planet remains a mystery to scientists trying to find out how the Earth was formed and what went into its creation. In a recent study, they were able to recreate the powerful pressures at the center of our planet, allowing scientists to glimpse its early existence and even understand what the earth's core might look like now.
They reported their discovery in the latest issue of Science. “If we figure out what elements make up the core, we can better understand the conditions under which the Earth formed, which in turn will give us more information about the early history of the solar system,” says geochemist Anat Shahar, based in Washington. at the Carnegie Institute of Science. It will also allow scientists to gain insight into how other rocky planets formed in our solar system and beyond.
Earth was formed about 4.6 billion years ago by countless collisions of solids ranging in size from Mars to a small asteroid. As the mass of the early Earth increased, its internal pressure and temperature increased.
This affected the way iron, which makes up most of the earth's core, chemically reacted with lighter elements such as hydrogen, oxygen and carbon, as well as heavier metals that separated from the mantle and entered the interior of the earth. The mantle is a layer directly below the earth's crust, and the movement of molten rock in this area sets tectonic plates in motion.
Scientists have long realized that temperature changes can affect the degree to which an isotope of an element such as iron becomes part of the core. This process is called isotopic fractionation.
However, until now, pressure has not been considered a critical variable affecting this process. “In the 60s and 70s, experiments were carried out looking for the consequences of such pressure, but scientists did not find anything,” says Shahar. "But now we know that the pressure at which they conducted the experiments (about two gigapascals) was not powerful enough."
In 2009, another research team published a paper in which they suggested that the pressure could affect the elements that entered the earth's core. Therefore, Shahar and her team decided to re-examine its effects, using equipment that creates pressure up to 40 gigapascals. This is much closer to 60 gigapascals, which scientists consider the average during the early formation of the Earth.
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In experiments carried out on an advanced photon source at the Carnegie Institution in Washington, the scientists placed small samples of iron mixed with hydrogen, carbon and oxygen between two diamonds. Then the planes of this diamond vise were pushed together, creating tremendous pressure.
Subsequently, the converted iron samples were bombarded with high-energy X-rays. “We are using X-rays to test the vibrational properties of the iron phases,” Shahar said. The different vibration frequencies indicate which isotopes of iron are among the samples.
Scientists have found that such powerful pressure does indeed affect isotopic fractionation. In particular, the research team found that the reaction between iron and hydrogen or carbon, which should be present in the core, should leave a characteristic trace in the mantle rock. But it was not possible to find such a trace.
“Therefore, we believe that hydrogen and carbon are not the main light elements in the core,” Shahar said.
But the combination of iron and oxygen could not leave traces in the mantle, as the experiments of scientists showed. Therefore, it is possible that oxygen could become one of the lightest elements in the composition of the earth's core.
These findings support the hypothesis that oxygen and silicon form the basis of light elements dissolved in the Earth's core, says Joseph O'Rourke, geophysicist at the California Institute of Technology in Pasadena, who was not involved in the study.
“Oxygen and silicon are abundant in the mantle, and we know they dissolve in iron at high temperature and high pressure,” he said. "Since oxygen and silicon are guaranteed to be in the core, other candidates like hydrogen and carbon have little chance."
Shahar said that her team intends to repeat the experiment with silicon and sulfur, which may be part of the core. Now that they have shown that pressure can affect fractionation, this team wants to look at the effect of pressure and temperature in combination. They believe that results may differ from when pressure and temperature are used alone. “We conducted our experiments on solid iron samples at room temperature. But when the core formed, everything was in a molten state,”Shahar said.
The findings from these experiments may be relevant to planets outside our solar system, scientists say. “The fact is that we only see the surface or atmosphere of exoplanets,” Shahar said. - But how does their inner part affect what is happening on the surface? The answer to this question will affect whether or not there is life on this planet."