What Is Amber? Fossilised Resin and the Things Caught Inside It
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Amber is tree resin that hardened and survived for millions of years, sometimes with an animal or a plant trapped inside. The preservation is extraordinary, the bias in what gets caught is severe, and the trade in it raises serious problems.
How it forms
Certain trees produce resin as a defence against damage and infection, and that resin is chemically quite different from sap, being a complex mixture of compounds that hardens on exposure to air. Most resin decays, and a small proportion is buried in oxygen-poor sediment where it polymerises over long periods, losing volatile components and cross-linking into a stable solid. The process takes millions of years, and intermediate material that has not completed it is called copal and is distinguishable by its softness and by dissolving in certain solvents. Amber floats in saturated salt water, which is one of the simplest tests, and it is warm to the touch and produces a distinctive smell when heated. Deposits occur worldwide with the best known from the Baltic region, from the Dominican Republic and from Myanmar.
What gets trapped
The contents are spectacular and heavily biased towards particular things:
- •Small insects and arachnids, which dominate by number since they were the animals on and around tree trunks
- •Plant fragments, flowers and pollen, which record forest composition directly
- •Feathers, and in rare cases portions of small vertebrates including lizards, frogs and a partial bird tail
- •Behaviour frozen in place, including insects mating, feeding, being eaten and carrying parasites
- •Air bubbles, which have been analysed for ancient atmospheric composition with contested results
- •Almost nothing from outside the immediate forest, since only what touched the trunk could be caught
Why the preservation is so good
The resin does several things at once that ordinary burial does not. It coats the organism immediately and excludes oxygen and microorganisms, halting decay before it starts. Its antimicrobial compounds actively inhibit the bacteria and fungi that would otherwise consume the tissue. It dehydrates the specimen by drawing out water. And it hardens into a transparent solid, so the organism can be examined without being extracted. The result is preservation of external structure at the level of individual hairs and scales, far beyond what compression fossils achieve, and specimens can be scanned to reveal internal structure. What is not preserved is usually the original tissue itself, since the interior is generally a hollow space or a residue rather than intact material, which is why claims about recovering ancient genetic material from such specimens have not held up under scrutiny.
The famous mistake
The idea that ancient genetic material could be recovered from insects in amber entered public awareness through a novel and a film and has a scientific history worth stating. Papers in the early 1990s reported recovering genetic sequences from amber-preserved insects, and those results attracted enormous attention. Subsequent work failed to reproduce them, and careful studies established that the reported sequences were contamination from modern sources, which is a pervasive hazard in the field and which better laboratory procedures and authentication criteria were developed to address. The underlying chemistry is against recovery, since genetic material degrades with time and the estimates for how long any useful fragment survives fall far short of the ages involved, even under favourable conditions. Ancient genetic material is genuinely recoverable from far younger remains, and the amber claim specifically is settled.
The trade problem
Amber from northern Myanmar has produced an extraordinary series of finds from the mid-Cretaceous, including feathered dinosaur material and an enormous number of insect species new to science. It is also mined in an active conflict zone, and reporting has established that the mines have been controlled by armed groups, that revenue has funded the conflict, and that conditions for miners are dangerous. Several journals and societies have adopted restrictions on publishing material collected from the region after specified dates, and the palaeontological community has argued about it publicly, with positions ranging from a complete moratorium to the view that refusing to study specimens does not help anyone and loses the science. Provenance is frequently undocumented, since material passes through dealers, which raises the separate problem that a specimen may not be from where it is claimed.
The takeaway
Tree resin excludes oxygen, kills microbes, dehydrates the specimen and hardens transparent, preserving external structure down to individual hairs. What is caught is overwhelmingly what touched a trunk, which biases the record severely towards small forest animals. Claims of recovering ancient genetic material have not held up, and the Myanmar deposits raise serious ethical problems that the field is arguing over.