Single crystal uranium-lead dating is one of the best all-around methods and gets used a lot for vanilla geological applications of Earth rocks; any rock that c

Single crystal uranium-lead dating is one of the best all-around methods and gets used a lot for vanilla geological applications of Earth rocks; any rock that contains trace amounts of the mineral "zircon" can be dated with this technique. Zircon is special because it tends to incorporate a lot of uranium when it crystallizes while excluding lead. As time passes after the zircon crystal cools, uranium decays into radiogenic lead, and by measuring the relative abundance of these two things in the crystal we can estimate the time since that zircon crystallized (with no lead inside) and get an "age" that tells us how long it has been since that zircon crystal was formed. Zircon is common in many types of igneous rocks, which are rocks that began in a molten state. The zircon crystals in an igneous rock are resistant to weathering (compared to feldspars, another common igneous constituent), so sometimes they end up as grains in sedimentary rocks and we can use a variation on the technique called "detrital zircon geochronology" to estimate the age of sedimentary deposits. Other systems (like samarium-neodymium) are most often used when trying to date things older than the Earth, e.g. meteorites. http://en.wikipedia.org/wiki/Radiometric_dating http://en.wikipedia.org/wiki/Radiometric_dating