DNA could be found within a fossil if the entire organism was fossilized. However, if the fossil was a mold or a cast, then DNA could not be extracted.
Most fossils are formed within sedimentary rocks. Once an organism dies, it falls to the ground. Sometimes organisms are slowly covered by sediments that fall and settle to the bottom of a liquid such as a pond, stream, or river. Over time, the sediments thicken and harden around the dead organism. The remains of the organism will naturally decompose over time or become mineralized. If the organism decomposes, then an impression of the organism may be left behind. This impression is classified as a mold fossil. If the organism is mineralized, then a 3D cast fossil of the organism may be created. Because the biomolecules and tissues of the organism are not preserved in either casts or molds, DNA cannot be extracted from such fossils.
However, sometimes the entire organism is preserved. This may occur in either amber (tree resin) or ice. In this case, the tissues of an organism may be preserved in such a way that DNA could be extracted.
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