Epsilon notation
Epsilon notation expresses very small isotope differences in parts per ten thousand, written ε.
Some isotope variations are so small that even parts per thousand are too coarse. Epsilon notation, written with the Greek letter ε, expresses deviations in parts per ten thousand from a standard. One epsilon unit equals a difference of 0.01 per cent.
Epsilon units are used for nucleosynthetic anomalies, such as ε54Cr and ε50Ti, and for radiogenic isotopes such as ε143Nd and ε182W. In the isotopic dichotomy, for example, carbonaceous chondrites have ε54Cr values around +1 or more, while Earth and ordinary chondrites are near zero or negative.
An even finer unit, mu (μ), measures parts per million and is used for the most precise work, such as tungsten-182 variations in ancient Earth rocks that record early mantle processes. These tiny numbers show the remarkable sensitivity of modern mass spectrometry and the subtlety of the fingerprints meteorites carry.
Related terms
Level: Expert Advanced