Because the concentration ratio of carbon-14 to carbon-12 is lower in old samples, contamination with a small amount of modern carbon causes a disproportionately large shift in apparent age, the effect becoming more serious with increasing age of sample. Thus in a sample which is 17,000 years old the addition of 1% of new carbon will cause the age to be too recent by 600 years, for a 34,000-year-old sample the same percentage causes an error of 4000 years and for a 50,000-year-old sample the apparent age will be 36,000 years.