This blog post examines how advances in science and technology influence legal judgments and why scientific techniques like radiocarbon dating are becoming increasingly important as evidence, using specific examples.
As science and technology rapidly advance and their influence expands into various aspects of daily life, the need for expert scientific knowledge in courtrooms is steadily increasing. Paternity testing through DNA analysis and criminal investigations using digital forensics techniques have already become commonplace. Recently, the use of scientific evidence based on dendrochronology has drawn new attention.
Dendrochronology refers to the scientific field that reconstructs the growth history and environmental conditions of individual trees by analyzing their growth rings. Most trees growing in temperate forests form one growth ring per year, and the width, shape, and chemical properties of these rings vary depending on the environmental factors the tree was subjected to. For instance, years with abundant rainfall produce wider growth rings, while drought years yield narrower ones. The unique patterns revealed by these consecutively formed rings provide fingerprint-like clues that allow precise estimation of a tree’s growth chronology.
Suppose in 2005, after felling a 400-year-old tree with 400 growth rings and analyzing its cross-section, a peculiar pattern was identified: five wide rings, five narrow rings, and then six wide rings consecutively appearing over a 16-year period from 1628 back to 1643. Meanwhile, an old timber used as a main beam in a nearby historical site showed only 332 growth rings from the tree’s core and surrounding area, and the exact time it was felled was unknown. However, if the same pattern as the aforementioned tree is found in the seventh ring from the edge of that timber, it can be concluded that the tree providing that timber was felled around 1650 and began growing around 1318. Furthermore, this method of comparing tree rings can be used to trace the tree ring record even further back in time by contrasting it with other pillar wood found within the site.
Thus, comparative dating using tree rings is not only widely applied as a scientific technique for estimating the production or construction dates of artworks and cultural properties, but also provides practical assistance in resolving legal matters. In the past, trees were often used as land boundary markers, making the verification of a tree’s age a crucial basis for resolving disputes. Tree-ring analysis has also played a significant role in criminal cases. It is widely known that the dendrologist Köhler was instrumental in identifying the perpetrator in the 1932 kidnapping and murder of the Lindbergh baby. He analyzed the wood used in a handmade ladder left at the crime scene, tracing when and where it was processed at a sawmill before being transported to a lumber yard near the crime area. Furthermore, he scientifically proved that the wood used in the suspect’s attic floorboards and part of the handmade ladder originally came from the same piece of timber, providing the decisive clue that solved the case.
The field where tree ring analysis holds the greatest potential for application is likely environmental litigation. For a long time, scientists have focused on reconstructing the history of climate fluctuations and predicting future climate change through longitudinal studies of the environmental information contained in tree rings. However, the information accumulated in tree rings encompasses not only ecological factors like precipitation or tree diseases but also exposure to heavy metals, radioactive contaminants, and other harmful chemicals. Analyzing this data can provide crucial evidence for determining when harmful substances began being released in a specific area. Within the broader field of dendrochronology, research specifically focused on these chemical characteristics is sometimes referred to separately as dendrochemistry.
Meanwhile, for the opinions of scientific and technical experts to function as practical and reliable evidence in court, certain requirements must be met. This is no exception for tree-ring analysis. This is because courts must meticulously review the potential for expert bias and error, as well as the risk that specific theories or analytical methods might constitute pseudoscience. In particular, interpreting environmental pollution through tree-ring analysis involves more variables than interpreting physical environmental changes, and its research history is relatively short. Nevertheless, the assessment that the scientific and technological foundation of these analytical techniques is maturing to a level sufficient to meet the expertise and verifiability required by courts handling environmental litigation is gradually gaining traction.
