Age concordance

Oberh F, Fischer H, Meier M (1990) High-resolution U- ° Pb zircon dating of Tertiary bentonites and the Fish Canyon Tuff a test for age concordance by single-crystal analysis. Geol Soc Australia 27 74 (abstr)... 

In addition to the assumptions of initial conditions, the validity of U-Pb methodology relies on closed system behavior of U, Pb and intermediate nuclides in the decay chain. Concordance between the two U-series decay chains is most likely to be compromised by Rn loss because Rn is the only gas in the decay chains and has a high diffusivity. Radon-222 in the decay chain has a half life of 3.8 days. This is much longer than the half-life of Rn (3.96 s) in the decay chain. Therefore, partial loss of Rn will give rise to an apparent age younger than the true age, whereas the 207p /235p ... 

Kaufman A, Broecker WS (1965) Comparison of °Th and " C ages for carbonate materials from Lakes Lahontan and Bonneville. J Geophys Res 70 4039-4054 Kaufman A, Ku T-L, Luo S (1995) Uranium-series dating of camotites Concordance between Th-230 and Pa-231 ages. Chem Geol 120 175-181... 

Shukitt-Hale B, Carey A, Simon L, Mark D and Joseph J. 2006. Effect of Concord grape juice on cognitive motor deficits in aging. Nutrition 22 295-302. 

Figure 11.14 (A) Internal Rb-Sr isochron for a system composed of three crystalline phases of initial compositions Aq, Bq, and Q formed at time t = 0 and thereafter closed to isotopic exchanges up to time of measurement t, when they acquired compositions A, and C. (B) Effects of geochronological resetting resulting from metamorphism or interaction with fluids. X, X2, and X3 bulk isotopic compositions of the three rock assemblages. In cases of short-range isotopic reequilibration, the three assemblages define crystallization age and original ( Sr/ Sr)o of the system the three internal isochrons (concordant in this example) define resetting age.

The ages of all samples are sufficiently concordant, indicating that they formed within a relatively short interval of time (about 90 Ma) ... 

The above results show that (i) all three ages are consistent within error (hence, the three ages are concordant) and (ii) the age calculated using the Pb/Pb method has the smallest error. 

Environmental factors, such as prenatal maternal infections and perinatal complications, have been implicated in the pathogenesis of schizophrenia. Also, the correlation of only 0.6 for age of onset in monozygotic twins concordant for schizophrenia suggests that non-genetic factors play a role in determining the age of onset (Kendler et ah, 1987). A greater frequency or severity of these factors could conceivably result in an earlier onset of schizophrenia. 

Ludwig, K., 1998. On the treatment of concordant uranium-lead ages. Geochim. Cosmochim. Acta, 62 665-676. 

The value of the decay constant (1) must have remained constant over the age of the solar system and the galaxy, and it must be accurately known. As we discussed in Chapter 2, this third assumption is well founded for conditions relevant to cosmochemistry. The concordance of dates given by systems using a variety of decay paths and astronomical observations of decay rates of newly synthesized elements over billions of years provides strong evidence that the decay rates have remained constant. In addition, detailed experiments and theoretical models have identified the extreme conditions (e.g. centers of stars) under which this assumption breaks down for certain isotopes, thereby identifying the exceptions that prove the rule. (4) It must be possible to assign a realistic value to the initial abundance of the... 

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