Boreskov

PL‐2case the primary Earth substance spent the initial 120 million years in dispersed condition, asparticles or small bodies.A similar situation is observed with regard to the U‐Pb system. There is a certain lack ofradiogenic lead isotopes 206 Pb and 207 Pb, as though the primary Earth’s lead had been lost.Some authors believe that it is due to early sink of the lead into the Earth core. However Pbway escape as a volatile element. Due to its high atomic weight, it could not have been lostfrom the surface of the planet. But it may have been easy lost from a hot surface of smallbodies and particles.Combined solution of equations for the 238 U‐ 206 Pb and 231 U‐ 207 Pb systems yields 120 mlnyears for consolidation of the Earth from the dispersed stay, right the same, that followsfrom 129 J‐ 129 Xe, 244 Pu‐ 136 Xe systems.Thus, the isotope systems data are in concordant agreement with an idea that a planetmay form through condensation of a particle cloud rather than by consequential growth of amassive planetary body. As regards the Earth‐Moon system, one may suggest that by thetime about 50‐70 million years had passed, the primary particle cloud undergonefragmentation, which result in separation and formation of the Moon, while fullcondensation completed in about 120 million years, when the Earth took shape as aconsolidated body.9