ERN Item Type:
- Classroom Activities
How do geologists understand the Earth’s history? In part, they measure the age of rocks and other natural materials by dating techniques. They can date rocks by gauging the amount of decay of radioactive elements. The time necessary for half of any given amount of one element (the “parent element”) to decay to become another element (the “daughter element”) is called the element’s “half-life.” Ice cores, for example, contain data about Earth’s past climate. Geologists use a dating technique called K-Ar geochronology to find the age of layers of volcanic ash in ice cores. The half-life of K-Ar is 1.25 billion years. By measuring the ratio of K to Ar in feldspar crystals in volcanic ash, geologists can determine the time of the eruption and, thus, the age of ice in which the ash is found. Once they determine the age of a volcanic ash layer, geologists can study the materials in that ice core layer for clues about climate conditions at that time. You can simulate the dating process with popcorn. Popcorn starts out as unpopped “parent” kernels. Heating causes the kernels to begin popping, thereby starting your simulated “radioactive decay clock” and producing popped “daughter” popcorns. The half-life of your kernel-popcorn material is the time necessary for half of the given kernels to become popcorns.