Virtually all gold deposits in the world, and other heavy metals in the earth's crust and upper mantle were on the surface of the planet due to the massive asteroid "bombarded" by which the planet has undergone after the "freezing" of its core, British geologists say in an article published in the journal Nature.
"Our work shows that a large part of all the precious metals, which play a key role in the industry and the economy of the world, appeared on the planet, by happy coincidence, when the Earth collided and swallowed about 20 eksatonn (10 to the 18th power tons) of asteroids", — said the head group of scientists Matthias Villbold (Matthias Willbold) University of Bristol (UK).
One member of the group, Stephen Murbat (Stephen Moorbath) from Oxford University, found fragments of ancient mantle in the so-called "greenstone belt" Greenland in geological formations Isua (Isua). Scientists estimate the age of the rock is 3.8 billion years old. The researchers believe that they are "floated" to the surface and froze almost immediately after the formation of Earth's core, before the asteroids began "bombing" of the planet.
It is believed that during the formation of the Earth "heavy" elements — iron, platinum, gold and other precious metals — "drowned" in the mantle of the planet and the solid metal core. On the other hand, in the earth's crust and upper mantle of these elements is much larger than predicted by the theory of the origin of the world. Most scientists explain this by the fact that large asteroids bombarded the Earth's surface after the formation of the nucleus, was left on the surface of the crust and the mantle of "raid" of gold and other heavy metals.
Villbold and his colleagues confirmed the "asteroid" the origin of stocks of "heavy" elements in the earth's crust, after having analyzed isotope tungsten-182 and tungsten-184 in Greenland rocks and in meteorites, chondrites — "building blocks" solar system.
As a rule, in the Earth's mantle ratio of tungsten and tungsten-182-184 is higher than in meteorites — on land radioactive hafnium-182 decays into tungsten-182, which does not happen in space due to the action of cosmic rays. The ratio of these isotopes of tungsten in the modern Earth's crust is much lower than the calculated values, which indicates a change in the composition of the mantle in the past.
Scientists found that the samples of ancient rocks contain 13% more tungsten-182 in comparison with the "modern" rock. In addition, they are a large number of other "heavy" elements, including osmium-187. According to the scientists, confirms the "earthly" origin of these samples, as no osmium in chondrites, any other "space" rock.
As geologists suggest this is due to the fact that chondrites with low tungsten-182 "dilute" the mantle of the early Earth. In addition to tungsten-182, these asteroids are "covered" Land of gold and other precious metals.