He was employed at Caltech's Division of Geological & Planetary Sciences at the time of writing the first edition.
He is presently employed in the Space & Atmospheric Sciences Group at the Los Alamos National Laboratory.
When the glass is turned over, sand runs from the top to the bottom.
Radioactive atoms are like individual grains of sand--radioactive decays are like the falling of grains from the top to the bottom of the glass.
Many Christians have been led to distrust radiometric dating and are completely unaware of the great number of laboratory measurements that have shown these methods to be consistent.
Many Christians accept this and interpret the Genesis account in less scientifically literal ways.You cannot predict exactly when any one particular grain will get to the bottom, but you can predict from one time to the next how long the whole pile of sand takes to fall.Once all of the sand has fallen out of the top, the hourglass will no longer keep time unless it is turned over again.Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.There are over forty such techniques, each using a different radioactive element or a different way of measuring them.It has become increasingly clear that these radiometric dating techniques agree with each other and as a whole, present a coherent picture in which the Earth was created a very long time ago.Further evidence comes from the complete agreement between radiometric dates and other dating methods such as counting tree rings or glacier ice core layers. Wiens has a Ph D in Physics, with a minor in Geology.His Ph D thesis was on isotope ratios in meteorites, including surface exposure dating.The passage of time can be charted by the reduction in the number of parent atoms, and the increase in the number of daughter atoms.Radiometric dating can be compared to an hourglass.