Interpretation of Measures

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Getting values and understanding their meaning and in particular determining the exact age of a rock since its solidification involves very good knowledge of the subject. The sources of errors are numerous, including when taking measurements and calculations, but the most common mistake comes from a lack of knowledge or unknowns about the petrogenesis of the meteorite, that is to say. The continuation of the processes that formed the rock whose most recent phases that alter its composition and effaced the traces of the old transformations.

The concentration of radioactive isotopes can be used to estimate the bombardment rate of cosmic shelves while the accumulation of stable species (for example, neon-21) makes it possible to measure the total time since the beginning of this bombing is – The time elapsed since the ejection of the parent body meteoroid that protected it from cosmic rays.

The vast majority of meteorites were exposed to cosmic rays for more than a million years. For chondritic meteorites, the fraction exposed to cosmic rays decreases fairly quickly as the age of exposure increases. Most ordinary chondrites have exhibition ages less than 50 million years old and most chondrites carbonged under 20 million years. Achondrites have ages between 20 and 30 million years. Siderites (ferrous meteorites) have a much wider range of exposure ages, which extends up to about 2 billion years.

PICs are often observed in the exposure age distributions of different meteorite groups; They probably reflect events related to major impact that disrupts large parent bodies.

In summary, the exhibition age ranges are explained by both the dynamic evolution of meteoroid orbits and the life of meteoroids after their collisions. The almost total absence of meteorites with exhibition ages less than 1 million years suggests that the orbits of future meteorites can not meet that of the land in many less than a million years. The numerical simulations support this idea and also predict that the orbital life periods of a meteor candidate before its impact on earth should fall much faster than the ages of exposure to cosmic rays. This suggests that these meteoric candidates spend a significant fraction of their time in the form of small bodies evolving in the asteroid belt until their orbits cross a resonance (a region where they undergo strong gravitational disturbances by the planets, in particular Jupiter) placing them on collision orbits with the Earth.

The general decline in the frequency of meteorites showing exhibition ages greater than a few tens of millions of years and the upper limit of most chondrites and achombritates (stony meteorites) of 50 million years agree with estimates according to which Half of a given meteorite population is eliminated by collisions in 5 to 10 million years. The longer exhibition ages of the Sidérites suggest that their higher cohesion strength allows them to survive much longer in space.

In these circumstances, discovering a multi-billion year old meteorite is therefore not only scientifically gratifying but very rare and make these survivors of the genesis of the very precious solar system. This explains that their market value is equivalent to that of gold or gems.

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