The fall of asteroids to Earth during the formation of the planet became the reason for the current appearance of the planet, the earth's crust and continents. This conclusion was reached by an international group of scientists from South Africa, Canada and Finland. The article of scientists was published in the journal Nature Communication.
Several billion years ago, in Catarchean, the Earth was subjected to intense bombardment by comets and asteroids, which caused the appearance of large areas of molten basaltic rocks. The thickness of such melts could reach tens of kilometers, and the diameter - thousands of kilometers. One such site is the Sudbury igneous complex in Canada, which formed approximately 1.85 billion years ago. At the impact of the asteroid, a layer of melt five kilometers thick was formed, heated to 1.7-2 thousand degrees Celsius. At present, the complex is composed of layers of such igneous rocks as gabbro, norite, diorite, and granophyre. The layers are believed to have arisen as a result of magmatic differentiation, in which rocks of various chemical compositions are formed from magma. However, this hypothesis has not yet been confirmed.
According to alternative hypotheses, magmatic differentiation of the melt in Sudbury is not possible. The impact of an asteroid in this case does not contribute to good mixing (homogenization) of molten rocks, and differentiation occurs even before the onset of crystallization, just as immiscible liquids are separated. According to scientists, if this is true, then we will have to admit that the formation of craters on rocky planets, including the Earth, does not make any contribution to the evolution of the crust.
In the new work, scientists reported the discovery in the Sudbury complex of large inclusions of melanorites with a diameter of ten to one hundred meters. The research results showed that they come from rock that was originally formed in the melt in the direction from top to bottom, but then collapsed due to tectonic processes. In addition, melanorites simultaneously grew upward from the base of the complex, which indicates that the melt was nevertheless initially homogeneous, which means that magmatic differentiation took place in it. Similar processes took place in more ancient melts on the Earth, the Moon and other planets.
According to scientists, the results of the study show that asteroid impacts made the earth's crust rich in silica. This allows us to revise the traditional scientific concepts, according to which the rocks with silicon dioxide, of which the continents are now composed, could have been formed only in the bowels of the Earth.