DNA and other organic compounds that form living organisms are very fragile and decompose easily after death. Although scientists in the 1990s claimed to have extracted preserved DNA from amber-fossilized insects, such as bees, beetles and termites, the preservation of DNA extracts in amber fossils remains very controversial among the scientific community today.
Unlike other fossilized materials, the chemical structure of amber changes very little over time. In addition to showing the fossil in three dimensions, amber's translucent nature allows the detailed observation of many external structures, such as the veins of leaves and eyes, wings and antennae of animals. In the Baltic region alone, about 750 species of ancient plants were found preserved in amber.
Amber-preserved fossils are likely to be small, because the resin was extracted in small quantities, usually too small to trap tree-dwelling animals. Although most amber fossils are small plant fragments and the forefathers of the modern insects and spiders, small vertebrates are sometimes found preserved in amber. The ancient preservation through amber resin is called mummification. During this process, the organism can shrink up to 30 percent of its original size.
With the help of microscopes, scientists in the early 20th century found out that amber fossils also showed well-preserved internal structures, such as muscles, bones and respiratory organs. The advent of the electronic microscope in the late 20th century made it possible to observe cells and their small structures preserved in amber fossils.