The (U–Th–Sm)/He method is a thermochronological technique that allows us to determine when a mineral cooled to low temperatures during its geological history.
It is one of the most widely used methods for studying:
Radioactive elements such as:
These particles eventually become helium atoms (^4He).
At high temperatures, helium escapes from the mineral. When the mineral cools, the helium begins to become trapped.
From that moment on, the “clock” begins to tick.
That is why the method indicates when the rock reached a certain temperature during its cooling.
The most common ones are:
The lab analyzes how much helium the crystal has accumulated and how much U, Th, and Sm it contains. This data is used to calculate the cooling age.
Difference from U–Pb
U–Pb dating of zircon indicates when the mineral crystallized. (U–Th–Sm)/He indicates when the mineral cooled.
That is why both methods are often used together.