going back 55,000 years. The most recent part, going back 13,900 years, is based on tree rings. Reference sequences European chronologies derived from wooden structures initially found it difficult to bridge the gap in the fourteenth century when there was a building hiatus, which coincided with the Black Death,. However, there do exist unbroken chronologies dating back to prehistoric times, for example the Danish chronology dating back to 352 BC. Given a sample of wood, the variation of the tree-ring growths not only provides a match by year, but can also match location because climate varies from place to place. This makes it possible to determine the source of ships as well as smaller artifacts made from wood, but which were transported long distances, such as panels for paintings and ship timbers. Solar storms Solar storms of known date, such as the ones in 774-775 and 993-994, can provide a fixed reference point in an unknown sequence as they cause a spike in carbon 14 in tree rings for that year all round the world. For example, wooden houses in the Viking site at L'Anse aux Meadows in Newfoundland were dated by finding the layer with the 993 spike, which showed that the wood is from a tree felled in 1021. Applications Radiocarbon dating calibration Dates from dendrochronology can be used as a calibration and check of radiocarbon dating. This can be done by checking radiocarbon dates against long master sequences, with Californian bristle-cone pines in Arizona being used to develop this method of calibration as the longevity of the trees (up to c.4900 years) in addition to the use of dead samples meant a long, unbroken tree ring sequence could be developed (dating back to c.6700 BC). Additional studies of European oak trees, such as the master sequence in Germany that dates back to c.8500 BC, can also be used to back up and further calibrate radiocarbon dates. Climatology Dendroclimatology is the science of determining past climates from trees primarily from the properties of the annual tree rings. Other properties of the annual rings, such as maximum latewood density (MXD) have been shown to be better proxies than simple ring width. Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous. Art history Dendrochronology has become important to art historians in the dating of panel paintings. However, unlike analysis of samples from buildings,