Аз като видя нещо такова тичам при една стара версия на Encyclopedia Britannica ('97). Ето малко инфо оттам:

The Solar System

ORIGIN AND EVOLUTION

With the rise of scientific inquiry in the Renaissance, investigators began to try to fit theories on the origin of the Moon to available data, and the question of the Moon's origin became a part of the attempt to explain the observed properties of the solar system. At first, the approach was largely founded on mathematical analysis of the dynamics of the Earth-Moon system. Rigorous analysis of careful observations, over a period of more than 200 years, gradually led to the conclusion that, because of tidal effects, the rotations of both the Moon and the Earth are slowing, and the Moon is receding from the Earth. Studies then turned back to consider the state of the system when the Moon was closer to the Earth. Throughout the 17th, 18th, and 19th centuries, different theories on lunar origin were examined in an attempt to find one that would agree with the observations. They can be divided into three main categories: coaccretion, fission, and capture. The coaccretion hypothesis suggests that the Moon and the Earth were formed together from a primordial cloud of gas and dust. This theory, however, cannot explain the large angular momentum of the present system. In the fission scenario, a fluid proto-Earth began rotating so rapidly that a mass of material was ejected and formed the Moon. Although this theory was persuasive, when examined in detail it failed to meet dynamical criteria; scientists could not find a combination of properties for a spinning proto-Earth that would eject the right kind of proto-Moon. According to the capture hypothesis, the Moon formed elsewhere in the solar system and was later captured by the strong gravitational field of the Earth. This model remained popular for a long time, even though it always had fundamental difficulties in celestial mechanics; braking a passing Moon into the right orbit seemed to require unlikely circumstances.

By the mid-20th century, at the dawn of space flight, additional constraints on the circumstances surrounding lunar origin had been applied. Of great importance is the fact that the Moon is much less dense than the Earth, and the only likely reason is that the Moon contains significantly less iron. Such a large chemical difference argued against a common origin for the two bodies. However, hypotheses of independent origin had problems too. Although the question remained unresolved even after the Apollo missions, the amount of information about the Moon was vastly increased by the Apollo samples and other observations. Finally, in the early 1980s, a model emerged that now has the support of most lunar scientists--namely, the giant-impact hypothesis.

In this scenario, set more than four billion years ago, the early Earth is struck a glancing blow by a body the size of Mars. Prior to the impact, both bodies have undergone thermal evolution so that they are differentiated. As a result of the titanic collision, a cloud of fragments is ejected and aggregates into a full or partial ring around the Earth and then coalesces into a proto-Moon. The composition of the ejected matter (highly depleted in volatiles and relatively depleted in iron) reflects an origin in which material from the mantle of the impactor and from the mantle of the proto-Earth were combined and experienced an enormous heating event. Computer modeling of the collision shows that, given the right initial conditions, an orbiting cloud as massive as the Moon could indeed have formed. The result of one such computer model is shown in Figure 35.

Once a proto-Moon was present in the debris cloud, it would have quickly swept up the remaining fragments in a tremendous bombardment. Then, over a period of 100 million years or so, the flux of impacting bodies diminished, although occasional collisions with large meteorites still occurred. Perhaps this was the time of the putative magma ocean and the formation of the ancient plagioclase-rich crust. After the Moon had cooled and solidified enough to preserve impact scars, it began to retain the huge signatures of basin-forming collisions. About 3.9 billion years ago one of these formed the great Imbrium basin and its mountain ramparts (see above Figure 30). About three billion years ago began the long sequence of volcanic events that filled the front-side basins with mare lavas.

In an effort to unravel the history of this period, modern analytical techniques have been applied to lunar rock samples, as discussed below. The mare basalts show a wide range of chemical and mineral compositions reflecting different conditions in the deep regions where, presumably because of radiogenic heating in the rock, primordial lunar materials were partly remelted and fractionated so that the lavas carried unique trace-element signatures up to the surface. By studying the past events and processes reflected in the mineral, chemical, and isotopic properties of these rocks, lunar scientists are slowly building a picture of a variegated Moon. Their findings have provided valuable background information for the remote-sensing observations that show how the content of important materials varies over the lunar surface.

Once the huge mare lava eruptions had diminished, apparently the Moon's heat source had run down. The last few billion years of its history have been calm and essentially geologically inactive except for the continuing rain of impacts, which is also declining over time, and the microscopic weathering due to bombardment by solar and cosmic radiations and particles.