Explanation: Radioactive elements decay at a certain constant rate and this is the basis of radiometric dating. But, the decay elements need to be set, much like you would re-set a stop watch for a runner, to ensure an accurate measurement.

Why cant Geologists date sedimentary rocks directly?

Why are geologists not able to date sedimentary rocks directly? Sedimentary rocks are younger than their composite minerals. The oldest known mineral grain is a 4.4-million-year-old zircon crystal found in an ancient sandstone. The sandstone is younger than 4.4 billion years old.