How to date with tree rings?

The principle of tree wheel method is very simple. Trees grow in spring and stop in autumn every year, forming dense and alternating circles on the trunk section, which are called annual rings. Once a year (or twice a year), the number of years on the cross section of the tree represents the age of the tree. The distance between wheels is the wheel tracks, but the wheel tracks are not equal, which is closely related to the climatic conditions at that time. The climate is warm and humid, plants grow vigorously and the wheel tracks are wide. If there is less rain, the track is narrow. In the same climate, the trajectory and shape of the same kind of trees are similar. If the annual ring spectrum of the inner layer of the living tree is consistent with that of the outer layer of the dead tree, it means that the dead tree grew in the previous stage, and the two can be related. Dead trees can be connected with older dead trees, and so on. By connecting different time intervals, the main tree-ring sequences (also known as standard tree-ring sequences and tree-ring synthetic tables) in this area can be established. It should be noted that the synthetic tree ring table is composed of tree ring diagrams of the same tree species in the same climate zone. The 8000-year standard sequence established in California, USA, is obviously completed by "interconnection". Some European countries have established some in this area.

Standard sequence in time range. In practice, the chronology of the standard sequence determined by this method is consistent with the calendar.

By comparing the tree ring spectrum of wood samples discovered by archaeology (as long as the number of tree rings exceeds 60-70) with the established main tree ring sequence table, the absolute age of life and death can be determined, and the accuracy can reach several years.

It is worth noting that the selection of tree species must meet the conditions of standard annual rings, that is, only one annual ring is added in a growing season, and it is sensitive to growth limiting factors. It is best to choose long-lived and widely distributed tree species. The United States chooses coniferous evergreen trees, Europe chooses oak trees and China chooses cypress trees. When collecting, collect wooden plates or wooden holes as appropriate. Then use a grinder or sandpaper to grind and rub the sample to make its surface smooth. Finally, the tree ring dating system is used to measure. The Archaeological Science and Technology Center of the Institute of Archaeology, Chinese Academy of Social Sciences uses the LINTAB annual ring measurement system, which consists of a binocular stereo microscope, a horizontal moving platform and a computer. When operating, aim the eyepiece reticle with a cross in the stereomicroscope at the annual ring to be measured, shake the handle by hand to make the movable platform move horizontally and drive the sample on the platform to move until the reticle is aimed at the next annual ring to be measured, and press the left mouse button, so that this horizontal distance is converted into a signal equivalent to the annual ring width by the sensor and input into the computer, the annual ring width data is recorded and saved by the computer, and the annual ring diagram is displayed on the computer screen. The age can be determined by comparing the obtained tree ring map with the established standard map. The unit analyzed the tree rings of Zhang Wan's tomb in Cixian county, Hebei province, and established the floating tree rings chronology of cypress in tomb 177.