Frequently Asked Questions on Biogenic Apatite
1. What equipment is used for biogenic apatite analysis?
The Isotopic measurements are done on the TC/EA-IRMS. The TC/EA is a high-temperature conversion unit that uses pyrolysis to thermally decompose the sample at 1400° turning it into Carbon Monoxide which is then measured on the IRMS.
2. Is the process destructive to samples?
The analysis on bioapatite is a destructive analysis as sample digestion is required. 30 mg is the optimum sample size, but depending on the amount of extractable bioapatite smaller sample sizes can be processed. For whole bones and/or teeth the sample requirements are sufficiently small that most of the specimen will be unaffected.
3. Is it possible to measure on cremated bones?
While we can measure heated bone samples it is important to note that such cremation can alter the original values and may not be representative of the values at the time of formation, which is why we do not combust samples to remove organics in our cleaning process. Thus for most purposes, samples should not be cremated/combusted/muffled.
4. Does the quality of biogenic apatite vary if the fossils are millions of years old? Have studies been done on dinosaurs?
There have been numerous studies measuring biogenic apatite on dinosaurs and other fossils of similar age. Quality as always is sample-specific and is more a function of the conditions of its preservation. It should be noted that questions concerning homeothermy in fossil organisms clearly influence the way in which that data is to be interpreted. Biogenic apatite specifically has been used to demonstrate body-part specific heterothermy in studied dinosaurs.
5. How do bones reflect altitude variations? Do different parts of the same bone yield different values?
Bone biogenic apatite reveals only minor variability in δ18O values regardless of which part the sample is taken from. The exception to this may be driven by differences in preservation with dense cortical bone showing better preservation. δ18O varies by altitude due to the rainout effect that preferentially condenses heavier isotopes. This results in the remaining vapor becoming more isotopically negative at higher altitudes (approximately 1 per mil per 1000 m). Because of the nature of bone growth however, a sudden change in altitude would be integrated into the longer-term isotopic value rather than be present as a discretely observable event. This contrasts with, for example, a tooth where such a temporal history can be reconstructed.
6. How are results reported?
Results are reported as δ18OPO4 corrected to VSMOW using a three standard regression. Uncertainties for each sample measurement is presented as the 95% confidence interval (CI).