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.
However, some Christians suggest that the geologic dating techniques are unreliable, that they are wrongly interpreted, or that they are confusing at best.
Unfortunately, much of the literature available to Christians has been either inaccurate or difficult to understand, so that confusion over dating techniques continues.
Some of the atoms eventually change from one element to another by a process called radioactive decay.
If there are a lot of atoms of the original element, called the parent element, the atoms decay to another element, called the daughter element, at a predictable rate.
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.
Rocks are made up of many individual crystals, and each crystal is usually made up of at least several different chemical elements such as iron, magnesium, silicon, etc.
Radiometric dating techniques indicate that the Earth is thousands of times older than that--approximately four and a half billion years old.
Many Christians accept this and interpret the Genesis account in less scientifically literal ways.
Many people have been led to be skeptical of dating without knowing much about it. In spite of this, differences still occur within the church.
For example, most people don't realize that carbon dating is only rarely used on rocks. A disagreement over the age of the Earth is relatively minor in the whole scope of Christianity; it is more important to agree on the Rock of Ages than on the age of rocks.