Isotopic Analysis
What is the evidence? Measurements of the amounts of isotopes of a given element in a sample, and calculation of the ratios; comparison of the isotope ratios in different materials
What does it tell us? A material’s isotopic signature—its isotope “fingerprint”—tells us where the material came from in the solar system.
Key limitations: Precision and resolution of the analytical instrument; not all elements in all materials can be measured; requires careful physical and chemical sample preparation; instrumentation is expensive; requires accurate measurements of a “standard” for comparison
Example: Oxygen Isotopes
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The amounts of oxygen isotopes in rocks from different places on Earth may vary, but their ratios will be the same. All rock samples from Earth plot along a line with a particular slope; this line is shown in the graph. This graph shows how the oxygen isotope ratios in rock samples from the Moon, Mars, and the giant asteroid Vesta compare to Earth.
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