(ORDO NEWS) — The new hypothesis links the zones of ultra-low velocity of propagation of seismic waves with the remnants of the matter of the young planet – and with the appearance of the Moon.
Between the crust and core of the Earth is the mantle, a thick layer of hot, slow-moving rock. It is not yet possible to achieve it with the help of drilling, therefore, scientists receive information about the structure of the mantle through seismic waves.
The speed of their passage makes it possible to draw conclusions about the composition and structure of the rock, to detect more and less dense areas and layers. For example , in the lower part of the mantle there are ” Ultra Low Velocity Zones ” ( ULVZ), areas hundreds of kilometers wide and tens of kilometers thick, passing through which seismic vibrations slow down dramatically.
The nature of ULVZ remains unknown, and a new article by geologists from the Australian National University, published in the journal Nature Geoscience, is devoted to this mystery . In it, Surya Pachhai and his colleagues consider the hypothesis that ultra-low velocity zones differ from the main mantle in composition and retain the remnants of the early Earth. Rich in iron oxides, they are located relatively close to the planet’s core and can affect its global magnetic field.
To investigate ULVZ, scientists traveled to the Coral Sea, located between Australia and New Guinea. This is an area of high seismic activity, which provides good opportunities for studying the deep layers of the Earth. After collecting the data, the geologists performed computer simulations of the different ULVZ structures and how they might affect the passage of seismic waves.
The results obtained were compared with the real signal, and after working out hundreds of thousands of options, a model was selected that, more precisely, corresponded to the observations. It assumes that ULVZs have a layered structure, which means that with a high probability they can be the remnants of extremely ancient matter of the Earth.
Pachhai and his colleagues suggest the following picture. More than four billion years ago, when the differentiation of rocks was still going on and heavy iron was sinking to the center, and lighter silicates were rising to the surface, the planet collided with a massive celestial body.
This catastrophe led to the appearance of the Moon, and left a deep “wound” on the Earth itself – a vast ocean of molten magma. It also divided the rocks into more and less dense.
Gradually cooling and solidifying, the substance retained such a layered arrangement. The ocean became islands that plunged deep into the mantle, becoming ultra-low velocity zones – layered dense areas in the middle of much better mixed rock.
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