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.
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.
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.
This paper is available on the web via the American Scientific Affiliation and related sites to promote greater understanding and wisdom on this issue, particularly within the Christian community.
Introduction Overview The Radiometric Clocks Examples of Dating Methods for Igneous Rocks Potassium-Argon Argon-Argon Rubidium-Strontium Samarium-Neodymium, Lutetium-Hafnium, and Rhenium-Osmium Uranium-Lead The Age of the Earth Extinct Radionuclides: The Hourglasses that Ran Out Cosmogenic Radionuclides: Carbon-14, Beryllium-10, Chlorine-36 Radiometric Dating of Geologically Young Samples Non-Radiogenic Dating Methods for the Past 100,000 Years Ice Cores Varves Other Annual-Layering Methods Thermoluminescence Electron Spin Resonance Cosmic Ray Exposure Dating Can We Really Believe the Dating Systems? Rightly Handling the Word of Truth Arguments over the age of the Earth have sometimes been divisive for people who regard the Bible as God's word.
There are over forty such techniques, each using a different radioactive element or a different way of measuring them.
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.
Similarly, when all the atoms of the radioactive element are gone, the rock will no longer keep time (unless it receives a new batch of radioactive atoms).
The rate of loss of sand from from the top of an hourglass compared to exponential type of decay of radioactive elements.