The isotope ratio is directly used for comparing oils or gases.
But the team found that on the Moon it was about 25 times that of the terrestrial chlorine isotope ratio.
The isotope ratios tell you about the bird's diet. And that tells you where they dined.
An obvious restraint in the use of isotope ratios results from the need to employ mass spectrometers.
Dr Sharp said that if lunar rocks had initial hydrogen contents anywhere close to those of terrestrial rocks, the chlorine isotope ratios would not have so much scatter.
Early in Earth's history, volcanic eruptions spewed massive amounts of sulfur dioxide into the atmosphere, where UV sunlight broke down the gas and created the odd sulfur isotope ratios.
Whatever caused the ancient fluctuations in isotope ratios, the researchers contend, those variations are a sign that climate back then varied from year to year just as it does today.
