This is in response to a question on the 2/20 thread asking if the length of time it took for the girls to be found would impact the usefulness of the DNA on the scene. For a long-dead subject, DNA has an expiration date, but its not as short as you think it is.
The entire formula for human life is encoded in the sub-microscopic molecules of deoxyribonucleic acid, and has been throughout all stages of evolution. Like fingerprints, genetic code is particular to an individual, which makes it a unique identifier in the absence of other information, like modern dental records. DNA, however, is fragile, and breaks down over time. How long the decomposition process takes will vary with the circumstances under which it is found. Take, for example, if DNA is exposed to the elements: Like the human body itself, DNA decays with increasing rapidity in the presence of heat, water, sunlight, and oxygen. Those essential conditions of life also speed the process of death, potentially rendering DNA useless for analysis in a matter of weeks. Since the girls were not found after that length of time there should be some very useful DNA, though transfer DNA from touch is a little trickier out in the elements.
The entire formula for human life is encoded in the sub-microscopic molecules of deoxyribonucleic acid, and has been throughout all stages of evolution. Like fingerprints, genetic code is particular to an individual, which makes it a unique identifier in the absence of other information, like modern dental records. DNA, however, is fragile, and breaks down over time. How long the decomposition process takes will vary with the circumstances under which it is found. Take, for example, if DNA is exposed to the elements: Like the human body itself, DNA decays with increasing rapidity in the presence of heat, water, sunlight, and oxygen. Those essential conditions of life also speed the process of death, potentially rendering DNA useless for analysis in a matter of weeks. Since the girls were not found after that length of time there should be some very useful DNA, though transfer DNA from touch is a little trickier out in the elements.