It is important to have a chronology to produce a pollen sequence in order to attach ages to particular events and estimate rates of change over time. There are numerous written sources dating back to AD 400 (AD 500-600) from the Romans, Greeks and Egyptians. The main forms of dating I will cover are radiocarbon dating, dendrochronology and tephrachronology. Radioactive dating is a technique used to date materials such as rocks, sediments and artefacts. Walker (2005) states that ‘Not only is the carbon atom the building block of life (…) it also provides us with a means of dating life’. Radioactive dating is based on the disappearance or development of an isotope because of radioactive decay (for example, artificially produced isotopes 137Cs/134Cs). Isotopes are atoms of elements with different numbers of neutrons. An atom is the smallest unit that defines the chemical elements and their atoms. The nucleus is situated at the centre of an atom and contains protons (positively charged …show more content…
A masterchronology is required for each climatic region. It is difficult to stabilise a floating chronology and difficult to overlap a sequence of these timbers. Sometimes the rings are doubled or there are ‘missing rings’. But also, when trees have fallen at a young age often there may not be enough rings on the tree to make an accurate cross-match. Often no cross-match can be identified. This could be due to the use of imported timber for example. To add to the confusion, often the date that the timber had fallen is not the same as the date of construction of a building it was used for. A surprisingly early date may suggest the use of salvaged timbers. Sapwood is highly susceptible to decay particularly by beetle larvae. As a result all sapwood may have been removed from the accessible surfaces of timbers during building repairs and conservation work, making it impossible to determine when the timber was