What is uranium lead dating
Thus, when a geologist dates a rock using uranium-lead dating, he or she is actually getting an estimate on the age of its zircon crystals, which formed "shortly" before the volcanic eruption.Of course, in this case "shortly" is meant in terms of geologic timescales.Because lead (the stable daughter of uranium) has a very different arrangement of electrons, it does not make its way into the crystal as it is forming.The formation of crystals in the magma marks the moment that the radio-isotopic clock starts ticking.Slightly different dating techniques are used with different radioactive elements, but the same basic logic of estimating backwards based on radioactive decay remains the same.The geology behind radioisotopic dating Though the basic logic behind radioisotopic dating relies on nuclear physics and quantum theory, many geologic processes also factor into our ability to date a particular rock. How do they know that the rock isn't contaminated with elements that would throw off the dating?
Geologists hunt for these particular sorts of rock to date the volcanic eruption in which the rock formed.Now imagine that you have a rock sample that contains 39% uranium-235 and 61% lead-207. At around 1000 million years (i.e., one billion years), as shown on the graph at right above.Thus, you would calculate that your rock is about a billion years old.Zircons are nearly perfect clocks because we can be relatively certain that when the crystal formed, no lead was present and that means that when we discover ancient zircons in rocks today, we can be relatively confident that any lead present is the result of radioactive decay.Geologists extract the appropriate minerals from the rock (in this case, zircon crystals) and use a technique called mass spectrometry to figure out the relative amounts of uranium and lead in the zircon.