Amber is the popular name for fossilized resin of botanical origin. The proper scientific terminology is fossil resin, but we will use the terms amber and fossil resin interchangeably. The word amber also denotes a golden color that amber predominately reflects (recall that when human eyes see color, it is actually the portion of the visible light spectrum that an object reflects that is detected). In fact, amber reflects many frequencies of light, including red, green and blue that together constitutes the entire visible spectrum. Archeological findings show that amber was one of the first materials prehistoric humans used for ornamentation, with instances dating back as far as 30,000 years. Use of fossil resin for jewelry and other decoration continues unabated, and amber is often considered as a gemstone.
Amber is also valued for its botanical and animal inclusions that are trapped by the sticky resin as it flows as sap, which is also organic. Of course, other life is captured including microscopic bacteria that often produce gas bubbles, and various fungi. Both the botanical and animal inclusions not only add beauty, but also are of potential scientific value in the study of taxonomy and evolution. Animal inclusions are usually invertebrates, specifically arthropods, and only extremely rarely a vertebrate such as a tiny lizard. Fossil resin inclusions are predominately insects, which should be no surprise since botanical resin is an evolutionary adaptation of plants that is, in part, for protection against insects.
Fossil Amber Chemistry
Fossil resin’s molecular constituency is mainly carbon and hydrogen atoms that readily form hexagonal rings. Molecular bonding between the rings increases over time (called polymerization), and the sticky resin becomes hard. There are other types of atoms in trace to larger amounts that alter physical properties and may be substrates to certain organic solvents. For all practical purposes, the hardened resin, or amber, is a “plastic”. Just when the resin becomes amber, or a fossil, is not defined, and is perhaps not definable. It is even contentious, since fossil resin is a commercial product in a competitive market. Younger amber is often called copal, though it is essentially as hard and its physical properties differ little from older resins.
All fossil resins are substrates for both hydrophilic (e.g., alcohol or acetone) and lipophilic (e.g., benzene) organic solvents and will disolve in them. The solvents will create various weak chemical interactions with the resin in order to solubilize it. The most common of these interactions are the relatively weak van der Waals interactions (induced dipole interactions), the stronger dipole-dipole interactions, and the even stronger hydrogen bonds (interaction between O-H or N-H hydrogens with O or N atoms).
Diamonds (and most mineral based gems) are forever, but fossil resin (amber) is not. As an unstable organic polymer, amber is biodegradable, just like a plastic milk jug or fiberglass boat. Its many weak covalent bonds and weaker hydrogen bonds are easily broken, a process that is accelerated by electromagnetic radiation of all frequencies and heat; ultraviolet is especially damaging (do not expose amber to sunlight), while visible and infrared much less so. Thus, while amber is, in a sense, the perfect preservative of fossils, once removed from the environment in which it formed, it is destined to crumble into dust; the time is long compared to the human lifespan, but essentially instantaneous on a geological timespan. Diamonds, on the other hand, go on forever.
Amber, Natural Selection and Chemical Warfare
Fossil resin (a.k.a., amber) is the result at least in part of nature’s oldest drama, predator versus prey. Science does not yet know when it appeared in the Kingdom Plantae’s arsenal of survival tactics, but natural section has conserved and probably diversified its usage. In temperate climates, the pines are prodigious producers of resin, which is used to make turpentine. In tropic climates, the genus Hymenaea, a timber tree, is the prolific producer. The evolutionary advantages of resin are varied. The resin is exuded to seal wounds such as from wind, fire, lightening or insect predation. Resin also contains a diversity of chemical defensive weapons. Some of these repel insects, and others attract insects that attack harmful insects, or attract parasites of insects that attack the plant, or are toxic to harmful fungi; in short a diverse chemical arsenal.
A Container for the whole Tree of Life
In terms of the Tree of Life, amber is most interesting since it entombs all three domains, Arachaea, Eubacteria and Eukarya. Archaea and eubacteria microbes are, of course, everywhere and surely embedded in the amber at high density. Interestingly, it is possible that some microbes. Still controversial finding a decade old claims to have recovered from the gut of a Hymenoptera from 30 million year old Dominican amber some three-dozen species of bacteria from ancient spores that grew on culture plates. The bacteria are from the extant genus Bacillus, a group that go dormant forming spores. Interestingly, Bacillus thuringiensis is used in the biological control of insects. Bacillus thuringiensis parasitizes the caterpillars of some harmful moths and butterflies. Spraying or dusting plants with its provides some protection against gypsy moth, tent caterpillar, and the tobacco hornworm. The bacteria has a gene that produces a toxic chemical warfare. The gene for this toxin has also been introduced into some crops.
Fossil Amber Ecosystems
One way to view amber is as a sealed unit containing a cross section of an ancient ecosystem with all its intricate predator-prey as well as beneficial symbiotic systems (e.g., termites as the methane produced by symbiotic bacteria that digest fiber in the termite gut). Fossil resin is a superb preservative, with organisms such as insects and spiders preserved in full three-dimensionality and in living color. To some degree, even, nucleotide sequence from ancient DNA is preserved, although resurrection of a Jurassic dinosaur is clearly science fiction.
Amber’s Geographic Dispersion
Amber comes from throughout the world, even the Arctic. However, in terms of commercial availability, the Baltic area of Europe produces vast amounts, followed by the Dominican Republic in a distant second, with minor amounts coming from Central and South America, and more specifically, Mexico and Colombia, respectively. Amber from other localities is miniscule.
An enormous amount of fossil resin is extracted on the shoreline of the Baltic Sea, and these strata are dated to be Eocene in age, give or take a few million years, thus making it some of the oldest amber that is available in commercial quantity. The largest Baltic amber mine is in Kaliningrad, Russia, but Baltic amber is also found in Lithuania, Latvia, Estonia, Poland, Russia, and sometimes washes ashore far away in Denmark, Norway, and England. Fossil inclusions are relatively rare, almost always in isolation and usually tiny, and the amber is normally occluded with botanical debris and bubbles; for this reason, fossil specimens are best made viewable in pieces cut to small size prior to polishing, and pictures many times require a trinocular microscope.