Mass spectrometer, used to measure the ration of atoms with different masses, in the USGS laboratory at Moffett Field, California

A mass spectrometer is used to measure the ratio of atoms with different masses—in this case, the different isotopes of argon gas, which can be used to determine the age of a volcanic rock. Left: a side view of a mass spectrometer at the USGS Argon Geochronology Laboratory in Moffett Field, CA. Right: a close-up view of the sample chamber in this mass spectrometer. Numbers 1 through 5 (right to left) and color-coded text boxes show the different parts and processes of the mass spectrometer. Photos by Genna Chiaro, 2024.