What Is Amber Fossilisation? Resin That Kept Whole Animals Intact

Resin is produced by certain trees as a defence, sealing wounds and trapping insects that attack the bark, and it is chemically quite different from sap, being a mixture of terpenes rather than a sugar solution. Fresh resin is sticky and volatile, and turning it into amber requires a long sequence: the volatile components evaporate, the remaining molecules polymerise into a cross-linked network, and burial under sediment subjects the mass to modest heat and pressure over millions of years, which completes the hardening. Material that has begun but not completed this process is called copal and is much younger, typically thousands to a few hundred thousand years, and it is softer, dissolves in solvents and is frequently sold as amber to people who cannot distinguish them. True amber is stable, insoluble in most solvents, hard enough to be carved and polished, and light enough to float in saturated salt water, which is one of the tests used to separate it from plastic imitations along with its behaviour when heated and under ultraviolet light.

Several properties of resin combine to protect what it traps:

• •It excludes oxygen and water immediately, halting the decay and microbial activity that destroy soft tissue in every other setting
• •It contains antimicrobial compounds produced by the tree as part of its defensive function
• •It dehydrates the trapped organism by drawing out water, fixing the tissues in place
• •It hardens gradually without crushing, so three-dimensional structure is retained rather than flattened as it is in rock
• •It is transparent, so specimens can be examined and now scanned with X-ray tomography without being extracted
• •It traps whatever else was nearby, including pollen, spores, hairs, feathers and fragments of the surrounding vegetation, which supplies environmental context around each specimen

Amber occurs worldwide and a few deposits dominate scientific and commercial supply. Baltic amber, around forty million years old and derived from an extinct conifer forest, is the largest commercial source and has been traded across Europe since prehistory along routes that carried it from the northern coasts to the Mediterranean. Dominican amber, younger and notably clear, is famous for its inclusions and includes specimens preserving whole lizards. Burmese amber, around a hundred million years old, is the richest scientific source for the Cretaceous and has produced extraordinary specimens including feathered dinosaur tail segments, primitive birds and a vast insect fauna. That deposit has also produced the field's most serious ethical problem, since the mines lie in a conflict zone in Kachin State and revenues have been connected to armed groups, which led several journals and professional societies to adopt restrictions from 2020 on publishing specimens collected after a specified date or without documented provenance.

The popular idea that dinosaur DNA could be recovered from blood inside amber-preserved biting insects made the material famous and does not work. Early reports of DNA extracted from amber specimens in the 1990s were subsequently attributed to contamination and have not been replicated, and careful attempts using modern methods have failed to recover authentic ancient DNA from amber at all, including from copal only a few thousand years old. The reason is chemical: DNA degrades through hydrolysis and oxidation on a timescale that puts a theoretical limit on survival of perhaps a million years under ideal cold conditions, and amber does not provide those conditions. What amber does preserve exceptionally is morphology, and that has turned out to be scientifically richer than the DNA idea promised, since three-dimensional specimens with intact hairs, mouthparts, genitalia and colour structures allow classification and behavioural inference at a level that compressed rock fossils never permit. Specimens have captured behaviour directly, including insects mating, feeding, caring for young and being parasitised at the moment the resin arrived.

Resin excludes oxygen and water, kills microbes chemically, dehydrates tissue and hardens without crushing, which preserves three-dimensional structure that rock fossilisation destroys. Copal is the same substance before the process completes and is much younger. Burmese amber is the richest Cretaceous source and sits in a conflict zone, which prompted publication restrictions. Ancient DNA has not been recovered from amber and chemistry says it will not be.