Meteroite Dating

How do scientists determine the age of meteorites, most of which are around 4.5 billion years old. –Amy


Meteorite Dating

Scientists measure the age of meteorites with the decay of radioactive isotopes. What is an isotope? Isotopes are elements with the same number of protons but a different number of neutrons. For instance, carbon-12 has 6 neutrons and carbon-14 has 8 neutrons. Some isotopes are very unstable and tend to decay into lighter elements by alpha or beta particle decay. Scientists use the half-life of certain elements to date objects. First, scientists must determine to isotope to use by examining the elemental composition of the object. For meteorites, scientists generally use Rubidium-87/ Strontium-87 decay, which has a half-life of 49 billion years. Rubidium-87 decays into Strontium-87. So if the object has 50% Rubidium-87 and 50% Strontium-87  (only formed by decay process), then the object is 49 million years old. Since some Strontium-87 may have been present originally, scientists use Strontium-86, whose content remains the same, as a reference. Determining the ratio between Rubidium-87/ Strontium-86 and Strontium-87/ Strontium-86 via mass spectrometer (vaporizes a tiny portion of the meteorite to form ions; the ions are then separated by mass in a magnetic field), scientists can then calculate the amount of each isotope present in the meteorite, and thus the age of meteorites. Although radioactive dating is the best method for scientists to date meteorites, many factors, such as the amount of sunshine or heavy rain, can affect measurements.