Uranium-lead dating facts for kids
Uranium-lead dating is a very old and accurate way to figure out how old rocks and minerals are. It's like a special clock that scientists use. This method can tell us ages from about 1 million years up to over 4.5 billion years! It is very precise, meaning it can be accurate within 0.1 to 1 percent.
This dating method works because certain types of uranium slowly change into lead over time. This change happens at a steady rate, like sand falling in an hourglass. Scientists measure how much uranium and lead are in a sample to find its age.
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How Uranium-Lead Dating Works
Uranium-lead dating uses two main "clocks" that run at the same time. These are called decay chains.
The Uranium-238 Clock
One clock starts with a type of uranium called Uranium-238 (238U). Over a very long time, this uranium slowly changes into Lead-206 (206Pb). It takes about 4.47 billion years for half of the Uranium-238 to change into Lead-206. This time is called its half-life.
The Uranium-235 Clock
The second clock starts with another type of uranium called Uranium-235 (235U). This uranium slowly changes into Lead-207 (207Pb). Its half-life is shorter, about 704 million years.
Having two different clocks running at the same time makes uranium-lead dating very reliable. Scientists can check the age using both clocks to make sure their results are correct. Sometimes, they might use just one clock, or even just look at the different types of lead to find an age.
Dating the Earth
A famous scientist named Clair Cameron Patterson used uranium-lead dating. He used it to figure out one of the first accurate ages for our planet, the age of the Earth.
Minerals Used for Dating
Uranium-lead dating is often done on a mineral called zircon (ZrSiO4). Zircon is a very useful mineral for this method because of how it forms.
Why Zircon is Special
When zircon crystals grow, they naturally take in uranium and thorium atoms. But they usually push out lead atoms. This is important because it means that almost all the lead found inside a zircon crystal was created from the uranium inside it. This lead is called "radiogenic" lead. If there is any lead that was already there when the zircon formed, scientists can correct for it.
Other Minerals for Dating
While zircon is very common, scientists can also use other minerals for uranium-lead dating. These include calcite, aragonite, and other carbonate minerals. These minerals might not give ages as precise as those from igneous (volcanic) or metamorphic (changed by heat and pressure) rocks. However, they are found more often in the Earth's rock record, which makes them useful.
Images for kids
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Figure 1: This is a Concordia diagram. It helps scientists see the ages of zircon samples from the Klamath Mountains in Northern California. The lines show ages increasing by 100 million years.
See also
In Spanish: Datación uranio-plomo para niños
