that ranged from 250 years to 3320 years. Contamination Any addition of carbon to a sample of a different age will cause the measured date to be inaccurate. Contamination with modern carbon causes a sample to appear to be younger than it really is: the effect is greater for older samples. If a sample that is 17,000 years old is contaminated so that 1% of the sample is modern carbon, it will appear to be 600 years younger; for a sample that is 34,000 years old, the same amount of contamination would cause an error of 4,000 years. Contamination with old carbon, with no remaining , causes an error in the other direction independent of age – a sample contaminated with 1% old carbon will appear to be about 80 years older than it truly is, regardless of the date of the sample. Samples Samples for dating need to be converted into a form suitable for measuring the content; this can mean conversion to gaseous, liquid, or solid form, depending on the measurement technique to be used. Before this can be done, the sample must be treated to remove any contamination and any unwanted constituents. This includes removing visible contaminants, such as rootlets that may have penetrated the sample since its burial. Alkali and acid washes can be used to remove humic acid and carbonate contamination, but care has to be taken to avoid removing the part of the sample that contains the carbon to be tested. Material considerations It is common to reduce a wood sample to just the cellulose component before testing, but since this can reduce the volume of the sample to 20% of its original size, testing of the whole wood is often performed as well. Charcoal is often tested but is likely to need treatment to remove contaminants. Unburnt bone can be tested; it is usual to date it using collagen, the protein fraction that remains after washing away the bone's structural material. Hydroxyproline, one of the constituent amino acids in bone, was once thought to be a reliable indicator as it was not known to occur except in bone, but it has since been detected in groundwater. For burnt bone, testability depends on the conditions under which the bone was burnt. If the bone was heated under reducing conditions, it (and associated organic matter) may have been carbonized. In this case, the sample is