Amber: Window to the Past  琥珀:通向过去的窗口

Amber is a form of tree resin(琥珀是由树脂形成的) -- exuded as a protective mechanism against disease and insect infestation -- that has hardened and been preserved in the earth's crust for millions of years. Often regarded as a gem, amber is actually an organic substance（有机物质） whose structure has changed very little over time, unlike that of other fossilized material, in which organic matter is replaced with minerals.

Because amber oxidizes and degrades when exposed to oxygen, it is preserved only under special conditions. Thus it is almost always found in dense, wet sediments, such as clay and sand that formed at the bottom of an ancient lagoon or a river delta. While hundreds of amber deposits occur around the world, most of them contain only trace amounts of the substance; only about twenty deposits in the world contain amounts of amber large enough to be mined.

Amber has preserved ancient life to such infinitesimal detail that it even captures fragments of DNA of the organisms entrapped in it. Such a wide variety of creatures has been found in Dominican amber, for example, that scientists are able to reconstruct this ancient ecosystem with amazing intricacy.