I was fascinated by the material provided for school teachers by the US Geological Society about dating rocks.
For a classroom activity they suggest:
Have your students look for evidence of date stamps and cornerstones on their walk home. Depending upon your area, there may be quite a few.
Duh! Building stones may have date stamps but rocks do not. This suggested activity makes the point, if anyone is alert to see it, that the only reliable way of knowing the age of anything is by the historical method, which relies on eyewitnesses and a written record. That is what the Bible is and why the Bible is the only reliable way of knowing the age of the earth.
More intriguing, they state the key concepts of the lesson as:
- Most rocks have tiny amounts of radioactive material in them.
- Radioactive elements decay (they change into a completely different element — for example, Uranium which is used in nuclear reactors changes into Lead, a very dense metal).
- Scientists use precise laboratory equipment to measure the amount of the new material that was created by radioactive decay.
- By knowing how fast certain elements decay, we can calculate the age of rocks (the number of years since the rock formed).
It all sounds very precise and technical but they leave out a key fact. It is impossible to calculate the age of a rock from such information because we need to know the radioactive content of the rock when it formed as well as the entire history of the rock until the sample was collected. In order to calculate a date the geologist first has to assume the geological history of the rock. In other words, all radioactive ages quoted are “guesses”, in that they are based on assumptions about the past.
The article is also wrong about its description of the dating of Grand Canyon.
Grand Canyon National Park, Arizona … In order to determine the age of an individual layer, a geologist must collect a sample of that layer and take it back to the lab. The geologist uses precise laboratory machines to analyze the relative abundance of radioactive atoms and atoms that form as a result of radioactive decay. Finally, the geologist can calculate the rock’s age. This calculation requires knowledge of math, physics, and chemistry! Note how the oldest rocks in the Grand Canyon are on the bottom and the youngest rocks are on the top.
Once again it all sounds very precise, technical and complicated. It seems designed to impress teachers and school children. But it is not true. The layers in the wall of Grand Canyon are sedimentary layers and sedimentary layers are not dated by radioactive methods, which are applied to igneous rocks. Rather, the sedimentary layers in Grand Canyon were “dated” using their contained fossil assemblages.
Check this article to see how radioactive dating works. This USGS item omits discussion on the fundamental problem facing every dating method—their fatal flaw. All radioactive dates are based on assumptions.
The USGS should fix this piece so it does not mislead teachers and school children.