Researchers from several laboratories later concluded that the DNA had actually stemmed from strands of human DNA that had contaminated Woodward's samples. The new technique allowed scientists to amplify tiny samples of DNA into amounts that could be analyzed in the laboratory. The drawback to this approach, however, is that tiny amounts of contaminating DNA could produce false results. Although several methods for authenticating ancient DNA have been proposed, most are extremely time-consuming and none are considered completely reliable. The approach used by scientists at Scripps and the University of Munich, however, relies on the analysis of the extent of racemization that has occurred in the amino acids aspartic acid, alanine and leucine.
Amino acids are the basic building blocks of proteins.
Living organisms use only L- amino acids. Because the racemization of aspartic acid, which has one of the fastest racemization rates, is similar to that for DNA depurination, it was found to be the most useful indicator of DNA degradation. Various levels of racemization were found to have occurred in other amino acids in the sample, suggesting that the amino acids were of different ages and thus probably represented contaminants. Not necessarily, according to Bada. So we haven't killed the idea that DNA is preserved in amber.