E R Matheau-Raven (UK)
Amber is the hardened resin of coniferous and angiosperm trees. Resin should not be confused with sap, which is a product of photosynthesis that consists of sugars, water and dissolved minerals. The sticky extrusive mass that comes from a cut on a pine tree is resin. Under the proper conditions, it undergoes certain physical and chemical changes that turn it into amber. If resin has hardened in recent times, it is called copal. Columbia, in South America, has extensive copal deposits.
Presently, certain trees produce large quantities of resin; the Kauri gum from New Zealand (Agathis australis), the Sundarac from Australia (Tetraclinis articulata), the Gum Arabic tree from Africa (Acacia arabica)and the Algarroba tree from South America (Hymenaea courbaril. It was trees like these that produced the resin that often trapped unsuspecting insects and even some slightly larger animals. Like ﬂy paper, the more the animal struggled to get free, the more entangled it became.
Often, the origin of the amber can be derived visually from the amber itself. Baltic amber may have a cloudy appearance, due to air bubbles and also has a high percentage of Succinic acid, as much as 8% by weight. It is a high-molecular compound of organic acids and has been produced as a result of fossilisation of the resin from the pine, Pinus succinifera. This tree was prospering in the Baltic area 40 to 45 million years ago.
Over time, the amber was re-deposited and concentrated far from its place of origin. The insect inclusions in Baltic Amber are represented by extinct species, although modern descendants inhabit subtropical and tropical regions today. The largest known amber deposits in the world are located in the north-western part of the Samland Peninsula, in Kaliningrad, Russia. It is so concentrated in the Eocene age Blue Earth strata, that it has been excavated for over 100 years in local mines and strip-mined from the surface, most notably from pits at Yantarnyi.
The Blue Earth layer varies in thickness between two to ten metres and yields an average 2.5kg of amber for each cubic meter. It derives its name and indeed colour from the high level of glauconite, an iron-aluminium silicate. Using absolute dating analysis of the glauconite, in 1997, Ritzkowski concluded that it formed during the Lutetian Stage of the Middle Eocene, some 40 to 50 million years ago. All the amber inclusions shown in this article are from the Yantarnyi deposit, Primorskoje Strip-Mine, in Russia.
Clear amber has been found in Tasmania and is estimated to be about 2 million years old. Dominican Republic amber, around 25 million years old, has little Succinic acid in it. Its colour is usually clear yellow, is a bit harder than other amber and it commonly has ants and beetles as inclusions.
Spectral analysis can be used to reveal the location and age of most amber. Amber comes in many colours. Typically, amber is golden yellow, but can also be green, red, blue and clear. Surprisingly, it is relatively stable and is insoluble even in many organic solvents. The ancient Greeks believed that amber was the petriﬁcation of sunrays; some even felt that it was petriﬁed tears. They prized amber for the magical (electrical) properties that it exhibited when rubbed. The term electricity is derived from the Greek word, elektron, which is also the Greek word for amber.
In modern times, different uses for amber have been found. In the 1800s, amber was melted and used as a ﬁnish on sailboats and other marine ships. Larger pieces of amber have been used by artists for sculpturing. Some has been melted down and re-solidiﬁed into ambroid for costume jewellery. The better-quality amber was and often is polished and used for jewellery.
The selective entrapping of insects and other small animals is a fascinating aspect of the fossil. Large animals are often strong enough to break free of the sticky resin, while small insects, such as ants, beetles, termites and spiders are usually not strong enough to break free from its hold. In New Jersey, USA the oldest worker ants have been found, dating from the Cretaceous, confirming that sociality has existed as far back as 100 million years ago.
Inclusions in amber are not fossils in the classic sense of the word, because most fossils are the imprint or bony remains of an organism. However, amber contains the actual animal itself. While, usually, all that remains is a carbonaceous crust, sometimes soft parts do survive. Recently, even the air bubbles that reside in different ambers have been analysed to determine the composition of the atmosphere at the time of its creation.
Combining beauty and history, Amber certainly is a golden snapshot of the past.
Microscope image supplied by Martin Stolworthy.
Amber: Tears of the Gods, by Neil D L Clark, Dunedin Academic Press, Edinburgh and London, with the Hunterian Museum and Art Gallery, Glasgow (2010), 118 pages, ISBN: 978-19-06716-16-5 (hardback), ISBN:978-19-06716-17-2 (softback)
Fossils in Amber: Remarkable snapshots of prehistoric forest life, by David Penney and David Green, Siri Scientific Press, Manchester (2011), 215 pages (softback), ISBN: 978-0-9558636-6-0; 126 pages (hardback), ISBN: 978-1-907701-02-3