New Research Opportunities in the Earth Sciences - New Research Opportunities in the Earth Sciences - page 83

Central Atlantic Magmatic Province yielded precisely the same age, providing
compelling evidence of a linkage between the extinction and massive volcanic
eruptions.
Figure 2.26 An example of the new insights possible with ages precise to a
small fraction of a percent. Chart shows carbon isotope variability in marine
carbonate in the early Cambrian period. High-precision U/Pb zircon ages of
intercalated tuffs shown in boxed numbers (in Ma). SOURCE: Maloof et al.
(2010). Reproduced with permission of Geological Society of America.
Similar advances have occurred in 40 Ar/ 39 Ar dating, which is important
because not all samples of interest contain datable zircons. Furthermore, the ability to
date coexisting minerals by two different high-precision methods allows the detection
of possible age biases arising from such factors as daughter product loss, inheritance,
and magma residence time. Much of the improvement in 40 Ar/ 39 Ar dating has arisen
from refinements to the 40 K decay constant (Renne et al., 2010) and to the ages of the
standards that are essential to the method. As an important example of standard
calibration, Kuiper et al. (2008) assigned extremely precise and accurate ages from
the astronomical timescale (counting of Milankovitch cycles) to ashfall sanidines in
Miocene sediments. These sanidines were analyzed for 40 Ar/ 39 Ar ratio and then used
to back-calculate the true age of the widely used Fish Canyon sanidine standard (the