Dating uranium 235
For example, if there is a piece of granite that has another kind of rock embedded in it, the inner rock will be older.
They map out the area and collect samples of this type of rock; then they take samples.
Scientists have many ways to discover how old rocks and fossils are.
The ratio of lead versus uranium in the zircon is what is used to determine the age of the rock. As you know, radioisotopes do not decay directly into a stable state; rather they go through stages of radioactive decay until reaching a stable isotope.
Uranium decay traps lead atoms in the crystal; these atoms get more concentrated over time.The zircons are studied with an electron microprobe; they hit the zircons with an electron beam to see the cathodoluminescent light that results after it.All of the atoms in the sample give off X-rays with different wavelengths after being hit with the electron beam, according to their atomic makeup.Also, zircons are magnetic so scientists can separate the finest pieces with magnets.Once they isolated zircon samples, this is when the hard part begins. Geologists take one tenth of one percent of the rocks and examine them.