Chondrites

Meteorites are the keys to understanding how Earth and the solar system formed because, although superficially many meteorites do not look significantly different from most Earth rocks close study shows that they are very different, With those differences holding clues to their distant origin. The most common type of meteorite-known collectively as the”chondrites-contains clues about the kinds of material that went into the construction of our planet.

The chondrites are just one of a variety of meteorite types, all ancient, but each with a different history-and each containing clues about how Earth and other planets formed and evolved. For example, the members of one group, the iron meteorites, are made up of solid iron metal, alloyed (or mixed )with a modest amount of nickel All the evidence indicates that these meteorites are similar to the metallic cores that inhabit the interiors of planets.

In contrast to the iron meteorites. the chondrites are made up of a jumble of mineral grains, many of them familiar constituents of rocks on Earth, but also including pure iron metal-which does not occur in rocks on Earth-and small marble-like spherical objects called”chondrules”(it is from these that the chondrites take their name). The chaotic texture of chondrites indicates that they were formed in a process that randomly swept together their different components and cemented them together. The texture is also an instant clue to one of their most important characteristics: they have never been melted. Furthermore, mineral grains in the chondrites have provided the oldest ages ever measured by radiometric dating they date from the very earliest days of the solar system. These two properties have led the geochemists who work on these intriguing objects to conclude that chondrites bring us something we cannot find on Earth or among other meteorite varieties: an unprocessed sample of the original material from which Earth and our neighboring planets were made. They appear to be unaltered samples of the solid matter that was floating around in the solar system just as Earth was being born; there is strong evidence that they come from small asteroids that never grew big enough to heat up and melt, as larger objects did.

The primitive nature of the chondrites has made them very important for information about Earths overall chemical composition. You might wonder why these rare rocks from space should play such a key role when the Whole Earth Is right below our feet, ready for us to analyze. The answer, In brief, is that if we want to understand how Earth got to its present state, we have to know something about its initial, overall composition. But we only have access to rocks from our planets thin outermost skin-which is very different from the inaccessible interior. However, by using information from the chondrites as a reference point, and integrating that data with direct measurements on surface rocks and information about the interior obtained using remote sensing methods, geochemists have been able to work out models for Earths overall composition that satisfy already obtained independent evidence such as the density of our planet.

An important concept in formulating these models is that the composition of Earth and the other”terrestrial planets(the solar systems inner, rocky planets, Mercury, Venus, and Mars)depends on the proportions of the main minerals found in the chondrites that each planet incorporated, A good example is iron, which is so abundant and so heavy that the well-known density variations among the terrestrial planets can almost entirely be attributed to differences in their iron contents. Grains of iron metal are abundant in the chondrites, but different chondrites contain different amounts. The reason Earth is much denser than Mars, according to the models, is that its chondrite-like building blocks happened to contain more iron. Similarly, other differences among the terrestrial planets can be understood in terms of different planets incorporating different amounts of the various constituents of chondrites. This is undoubtedly an overly simplistic description of what actually happened, but that does not invalidate the chondrites as a good starting point for understanding the composition of Earth and other planets.

1.Meteorites are the keys to understanding how Earth and the solar system formed because, although superficially many meteorites do not look significantly different from most Earth rocks close study shows that they are very different, With those differences holding clues to their distant origin.?The most common type of meteorite-known collectively as the”chondrites-contains clues about the kinds of material that went into the construction of our planet.?