Metamorphism and Age

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In addition to long-life radionuclides, a number of short-life radionuclides were present in the primitive solar system. Most of them have half-lives below a few million years. They have been disintegrated for a long time and can not be used to directly get absolute ages. However, their original abundances in some objects can still be determined by the isochronous method.

By comparing the original abundances of a short-lived radionuclide in different objects, scientists can determine their relative age. If one or more of these objects could also be dated using long-life radionuclides, the relative ages can be converted into absolute ages.

Attempting to determine absolute ages for relative ages determined from various short-life radionuclides has been the subject of much research, but it is always difficult. Indeed, short-life radionuclides generally behave chemically very differently from each other and long-lived isotopes. Nevertheless, given the seniority of meteorites, scientists have developed a remarkably accurate image of the synchronization of events during the genesis of the solar system.

The oldest objects contained in elderly meteorites of about 4.567 billion years are refractory inclusions (CIA). With few exceptions, they are also the most abundant objects in short-life radionuclides. But these are not the oldest elements discovered in a meteorite which are silicon carbide grains aged 7.5 billion years discovered in murchisonal chondritis.

The absolute ages of the Chondres have not been accurately measured, which is why the age of chondrites only relative to a scalable phase (for example less than 10 million years after the formation of the solar system). But indirectly and informally (never in univestandards) we deduce that these meteorites are aged at least 4.56 billion years as the meteorite of Semarkona presented below on the left.

The abundances of the short aluminum-26 radionuclide in the chondres of ordinary and carbon chondrites have been interpreted as the result of a training on a prolonged period of between 1 and 10 million years after the refractory inclusions. One of the oldest is the semarkona meteorite presented below on the left, one of the rare chondrites of type LL3 which formed about 2 million years after the formation of the solar system.

But the debate is open to the question of whether these ages, especially the most recent, are really worthy of the formation of the Chondres or would not rather date from the reset of their isotopes by subsequent processing processes. Metamorphic.

The visible metamorphism in ordinary chondrites ended between 5 and 55 million years after the formation of refractory inclusions, and in chondrites embedded between 9 and 34 million years. This very old but quite short period probably reflects both the size of the chondritic parent bodies and the depth to which the materials forming these meteorites were created in their parents parents. Indeed, the larger stars cool more slowly, just like the deeper regions of a star.

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