Amber, a fossilized tree resin, has been prized for jewelry since Neolithic times and is an invaluable subject for scientific inquiry. This organic gemstone offers a unique window into ancient ecosystems, often encasing remarkably preserved life forms. Understanding its formation involves a journey through geological time and specific natural processes.
The Starting Point: Tree Resin
Amber’s journey begins with tree resin, a viscous substance distinct from tree sap. While sap transports water and nutrients, resin is secreted by certain trees, primarily conifers, as a protective mechanism. When a tree is injured, resin oozes out to seal the wound and defend against fungi, insects, and disease. This sticky material forms a barrier that deters burrowing organisms. Not all tree resin possesses the chemical stability required for fossilization; only specific types can become amber.
Initial Hardening: Resin to Copal
The first phase of transformation sees fresh resin harden into copal. This initial hardening involves the evaporation of volatile components and polymerization, a chemical process where smaller molecules bond to form larger, more stable ones. Copal is an intermediate stage in amber formation, typically thousands to a few million years old. Unlike true amber, copal remains softer and contains volatile compounds, making it more susceptible to solvents like alcohol.
Deep Burial and Maturation: Copal to Amber
The complete transformation from copal to amber requires extensive geological processes over millions of years. Copal must be buried under layers of sediment, such as sand or clay, which protects it from decay by limiting oxygen exposure. Over geological timescales (10 to 300 million years), the buried copal is subjected to immense pressure and heat from the Earth’s crust. These conditions drive further polymerization and chemical changes, including the loss of volatile compounds like terpenes. This diagenesis results in the formation of a stable, inert polymer: amber.
What Preserves Inclusions?
One of amber’s most captivating features is its ability to preserve ancient organisms, known as inclusions. These occur when small organisms, such as insects, spiders, or plant matter, become trapped in fresh resin before it hardens. The viscous resin ensnares them, preventing escape. As additional layers of resin flow over the trapped organism, it becomes completely encased, sealing it off from the external environment. This encasement protects the organism from decay by limiting oxygen access and promoting dehydration, allowing for remarkable three-dimensional preservation over geological timescales.