Age reset

The aging process is reversible and repeatable. Whenever the capacitor is heated to a temperature above the Curie point, reset occurs and the aging process starts again from zero. Age reset can be formally assured by heating the capacitor for one hour at 125°C or for half an hour at 150°C. 

There are apparently customers who soldered on ceramic capacitors in their power supplies and found the clock was just too low. They figured the capacitance was above the guaranteed upper tolerance band (a rare event with commercial ceramics ), and shipped them right back to their manufacturers. But the problem was only that as soon as the PCBs went through the soldering process, age reset (or de-aging) occurred and so capacitance rose. If only they had waited for some more time, their clocks would have been right on However, I would have preferred SMD him capacitors if stability was so important. 

Zeck H. P. and Whitehouse M. J. (2002) Repeated age resetting in zircons from Hercynian-Alpine polymetamorphic schists (Betic-Rif tectonic belt S, Spain)—a U-Th-Pb ion microprobe study. Chem. Geol 182(2-4), 275-292. 

Bickle, M. J., Chapman, H. J., Bettenay, L. F., Groves, D. I. De Laeter, J. R. 19836. Lead ages, reset rubidium-strontium ages and implications for the Archaean crustal evolution of the Diemals area. Central Yilgam Block, Western Australia. Geochimica et Cosmochimica Acta, 47, 907-914. 

Many Himalayan Th-Pb monazite age data are difficult to interpret when results from a single rock are inconsistent with a single population (see also Foster et al. 2000). Monazite growth in metapelites may be due to dissolution of existing detrital grains or allanite breakdown. The dissolution/reprecipitation process is a possible age resetting and... 

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.

PI and P5 represent the age of the granite, and agree with previous dating (Rimsaite 1982). P3 represents the age of the pegmatite. P2 and P4 overlap and represent an event that reset monazite in both the granite and pegmatite, and corresponds to the age that Fowler Doig (1983) obtained by whole-rock Rb-Sr methods. 

This is exploited in the technique of uranium-thorium dating, which involves measuring the amount of thorium-230 that has accumulated in a substance by decay of uranium. If the object contained no thorium at all when it was formed, the ratio of remaining U to accumulated °Th is a measure of the age. The object being dated must not have had access to sources of fresh uranium that could reset the clock. This is true, for example, of coral left stranded on fossil beaches when sea levels recede, or of... 

The geologic timescale for the Earth is based mostly on stratigraphy (the depositional succession of layers from bottom to top). Most strata are sedimentary rocks. The relative ages of the sedimentary layers are determined by the sequence of deposition and by the fossils that they contain. It is not possible to use radioactive isotopes to measure the time that a sediment was deposited, because deposition does not reset radiometric clocks. However, the absolute ages of sediment layers and the fossils they contain have been determined by measuring radiometric ages of volcanic ash layers in the sequence or lavas that crosscut sedimentary strata. 

Impact ages of meteorites and lunar samples can be determined from radioisotope chronometers that are reset by shock. These involve radiogenic nuclides that are gases... 

On the other hand, vessels must often be derated for age and excessive corrosion. Either way, the relief valve needs to be reset. There is only one way to know the actual relief-valve setting, and that is to climb up to the relief valve and read the tag that was fixed to the valve at the time of its last setting. 

Figure 10.1. A generalized diagram for the steady-state rock cycle. Sediments, S, and continental crystalline crust, C, masses are in units of metric tons. Ss, Cs, Sc, Cc, and M are fluxes in units of 109 tons y-l due to erosion of sediments, metamorphism, erosion of crystalline rocks, recycling of crystalline rocks (resetting of ages during tectogenesis), and cycling of oceanic crust, respectively. Total sedimentation rate is 9 x 109 tons y-l. (After Gregor, 1988.)...

McCoy T. J. (1995) Silicate-bearing HE irons early mixing and differentiation in a core-mantle environment and shock resetting of ages. Meteoritics 30, 542-543. 

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