Les éléments volatils auraient été accrétés très tôt dans l'histoire de la Terre. © sdecoret, Adobe Stock

Where do the carbon, nitrogen, and water that made the Earth habitable come from? Even today, this question is still intensely debated. However, one chemical element in particular can help solve this puzzle, or at least advance the path of knowledge. This is Krypton. Its presence within the Earth’s deep mantle enlightens us on the composition of our planet.

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When and from what source the volatile elements arrived Like carbon, nitrogen, and water ? There are several models. Some studies indicate that the assimilation of these chemical elements occurred before the giant impact that led to the emergence of the moon, and others who were to come after him. Three main sources are also mentioned to explain the volatile element composition of tr : the SoleilAnd Chondrite (meteorites rich in Carbon coming from outside solar system) and the comets.

Krypton, a good chemical tracer

In an attempt to narrow down the question of the origin of the volatile elements, a team of researchers from the University of California has investigated the formation of the Earth’s lower mantle. Scientists have tracked in particular the existence of the different isotopes the krypton, a chemical element from a family Gas noble. Being inert, the noble gases are actually good tracers for the sources of volatile elements. Krypton, in particular, is very useful in distinguishing solar sources from cartilaginous sources thanks to the rather obvious isotopic differences.

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For their study, the researchers went to take samples volcanic rocks produced by volcanoes From Hotspot in Iceland and the Galapagos. In fact, the magma The nourishment of these volcanoes comes from a very deep area in Earth’s mantle, near the border with the outer core. Therefore, the formation of erupting igneous rocks represents a primitive mantle, of which The chemical composition has changed little since the formation of the Earth, 4.4 billion years ago. The magma rising from these very deep regions in particular is made up of some noble gases. When they reach the surface thanks to the operations bangsThe magma will then trap these gases in the form of small pockets, which will form tiny bubbles as the lava crystallizes. The researchers set out in search of a specific element within these bubbles: krypton. Measurements require the development of a new analysis technique, based on mass spectrometry. Thus various isotopes of krypton, particularly the rarest, such as Kr ., have been measured78 and Kr80.

The composition of the Earth’s mantle is very close to that of chondrites

The results are published in temper nature, showed that the chemical signature of the current lower mantle is very close to that of Chondrite, primitive meteorites rich in carbon originating outside the solar system. On the other hand, studies of neon, another noble gas found in the Earth’s lower mantle, appears to have originated in the solar system. These two findings indicate that the volatile elements collected during the formation of the Earth come from at least two different sources: rocky bodies from deep space and also Earth-forming materials. nebula Solar primitive. These elements could have been incorporated very early into the Earth’s formation.

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In fact, isotopes of krypton suggest that minor planets from outside the solar system would have bombarded the Earth millions of years before the moon formed. But at the same time, our planet would also have sucked in dust and gases from the solar nebula. This hypothesis is not only valid for Earth, but will also explain the composition of others Planets of the solar systemEven those who revolve around others stars.

These new findings also have implications for how Earth’s atmosphere formed. Because researchers have discovered that the ratio between the different isotopes of krypton is not the same in the atmosphere as in the lower mantle. This indicates that some gases from the atmosphere were also brought to Earth after the giant impact that gave birth to the Moon. Otherwise, the two environments, the atmosphere and the mantle, would have the same isotopic composition.

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