Pb pb dating

Posted by / 23-Jul-2017 21:49

Pb pb dating

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The combination of these ages with the corresponding metamorphic phosphate ages provides constraints on the thermal history of the different chondrite parent bodies.

Chondrules and pyroxene–olivine fractions from the ordinary chondrites yield ages that reflect the blocking of Pb isotope equilibration with the nebular gas.

Although this column and its ‘age’ was firmly settled well before the advent of radiometric dating, the latter has been used to quantify the, ‘ages’ of the strata and the fossils in the column, so that in many people’s minds today radiometric dating has ‘proved’ the presumed antiquity of the earth.

However, it is important to remember that all radiometric dating methods are based on three main assumptions:— The highly speculative nature of all radiometric dating methods becomes apparent when one realizes that none of the above assumptions is either valid or provable.

We suggest a thermal evolution model for the growth of the planetary bodies based on the release of radiogenic heat from Fe.

Planetesimals were already forming by ∼1 Myr after CAI formation, consistent with their growth predominantly through the accretion of chondrules.

Nebular chondrule formation was completed by ∼5 Myr after CAI formation when the impact-generated Cba chondrules formed after the disk was cleared of gas and dust.

Furthermore, the stepwise leaching technique has the advantage over multi-phase Pb Pb dating in that it does not require initial Pb isotope equilibrium among the phases, but may be used to test it.

The presence of microscopic solid inclusions, which complicate dating of single phases if they are not in equilibrium with the host, can be traced via the behaviour of the Pb ratio through the various leaching steps.

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by Andrew Snelling As with other radiometric ‘dating’ methods, the U-Pb and Pb-Pb isochron methods have been questioned in the open literature, because often an excellent line of best fit between ratios obtained from a set of good cogenetic samples gives a resultant ‘isochron’ and yields a derived ‘age’ that has no geological meaning.