For thousands of years, people have collected amber for its warm golden colour. It has been carved into beads, worn as jewellery and traded across long distances. However, amber is more than an attractive stone. In fact, it is not a stone at all. Amber is the fossilised form of resin, a thick and sticky substance produced by certain trees. For scientists who study the ancient world, it is one of the most valuable natural materials on Earth, because it can hold tiny plants and animals exactly as they were millions of years ago.
Many people believe that amber comes from tree sap, but this is a common mistake. Sap is a watery liquid that carries sugar and nutrients through a plant. Resin, on the other hand, is much thicker and acts as a kind of defence. When a tree is damaged, for example by a storm or a boring insect, resin flows out and covers the wound. It seals the opening, and it also traps or drives away insects that might attack the tree. Some modern trees, such as pines, still produce large amounts of resin today, and the sharp smell of a pine forest on a hot day comes partly from this substance.
Not all resin becomes amber. First, the resin must be buried quickly, usually in soil or in the sediment at the bottom of a river, lake or coastal lagoon. Without this protection, sunlight, air and rain break it down within a few years. Once buried, the resin slowly loses its lighter chemicals, and its molecules join together into long, strong chains. This process takes an extremely long time. Partly hardened resin that is only a few thousand years old is called copal. Copal looks similar to amber, but it is softer and becomes sticky when it is warmed. True amber is generally several million years old, and the oldest known pieces formed long before the first flowering plants appeared.
The objects found inside amber are known as inclusions, and they are what make amber so important to science. The most common inclusions are insects, such as flies, ants and beetles, which landed on the sticky resin and could not escape. In addition, researchers have found spiders, mites, seeds, flowers, pollen and even small feathers. On rare occasions, larger animals have been discovered, including tiny lizards and frogs. Because the resin surrounded these creatures completely, it kept out air and water and slowed down decay. As a result, details such as the hairs on an insect's leg or the patterns on a wing can still be seen clearly under a microscope.
Amber can also record moments of behaviour that are almost never preserved in rock fossils. For example, some pieces contain a spider in the middle of wrapping its prey in silk. Others show ants carrying their young or tiny mites riding on the backs of larger insects. One piece might even hold a parent insect beside its eggs. Ordinary fossils usually show only the hard parts of an animal, such as bones or shells, and these are often flattened over time. Amber, however, keeps soft bodies in three dimensions. For this reason, it offers scientists a rare chance to see how ancient animals lived and interacted with one another.
Despite these benefits, amber does not give a complete picture of a prehistoric ecosystem. One problem is that it mainly captures small organisms that lived on or near tree trunks. Large animals were strong enough to pull free from the resin, so they are almost never found inside it. Similarly, creatures that lived in open grassland or deep water had little chance of being trapped. Another popular idea is that scientists could recover ancient DNA from insects in amber and use it to bring extinct species back to life. This idea became famous through fiction, but careful studies have shown that DNA breaks down far too quickly to survive for millions of years, even inside amber.
Today, new technology is helping researchers learn more from amber than ever before. In the past, scientists often had to cut or polish a piece to see an inclusion clearly, and this sometimes damaged the specimen. Now, X-ray scanning machines can produce detailed three-dimensional images of the inside of a piece without touching it. These images can be enlarged, rotated and shared with experts around the world. At the same time, collectors and museums must be careful, because fake amber made from plastic or glass is sometimes sold. One simple test is to place a piece in very salty water: real amber usually floats, while many imitations sink. With careful study, each small piece of golden resin can continue to reveal the secrets of forests that disappeared long ago.