How to use a measuring microscope
How to use a measuring microscope: The principle of the tree ring method is very simple. Trees last in spring and autumn every year, and form dense and alternate circles on the trunk section, which are called annual rings. One round (or two rounds) per year, the age number on the tree section represents the age of the tree. The distance between the wheels is the wheelbase, and the wheelbase is not equal, it is closely related to the weather conditions at that time. The climate is warm and humid, and the plants grow vigorously, so the wheel base is wide. If there is drought and little rain, the wheel base will be narrow. Trees of the same species in the same climate are similar in wheelbase and shape. If the annual rings of a section of the inner layer of a living tree are consistent with the outer ring spectrum of the dead tree, it means that the dead tree grew in the previous stage, and the two can be connected. Dead trees can be connected with older dead trees, and so on, and the main tree ring sequence (also known as standard wheel track sequence, synthetic tree ring table) of this area can be established by connecting the wheel bases of different time periods. It should be noted that the synthetic tree ring table is formed by concatenating the tree ring maps of the same tree species in the same climate zone. The eight-thousand-year standard sequence established by the state of California in the United States is obviously completed by the method of "interconnection". Some countries in Europe have established standard sequences within certain age ranges in the region. From a practical point of view, the standard sequence chronology determined by this method is consistent with the calendar.
By comparing the annual ring spectrum of wood samples found by archeology (as long as the number of annual rings exceeds 60-70 rings) with the established main annual ring sequence table, the absolute age of its life and death can be determined, and the accuracy can reach several years. Difference.
It is worth noting that the selection of tree species must meet the conditions for the generation 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 tree species with longer life spans and wider distribution. The United States chooses coniferous evergreen species of pinaceae, Europe chooses oak trees, and my country chooses cypress trees. When collecting, depending on the situation, either collect wood discs or collect wood cores. Then use a sander or sandpaper to grind and rub the sample to make the surface smooth. Finally, measurement microscopy was performed with a dendrological dating system. The Archaeological Science and Technology Center of the Institute of Archaeology, Chinese Academy of Social Sciences uses the LINTAB tree-ring measurement microscope system, which consists of a binocular stereo microscope, a horizontal moving platform and a computer. When operating, first align the reticle of an eyepiece with a cross in the stereo microscope with the annual ring to be measured, and shake the handle by hand to make the movable platform move horizontally to drive the sample on the platform to move until the reticle is aligned with the annual ring to be measured. For the next growth ring of the microscope, press the left button of the mouse, so that this horizontal distance is converted by the sensor into a signal equivalent to the width of the growth ring and input to the computer. The data of the growth ring width is recorded and saved by the computer, and displayed on the computer screen. Annual ring map. Comparing the obtained annual ring map with the established standard map, the age can be determined. The unit conducted a tree-ring analysis of the wood from the Wanzhang Tomb in Ci County, Hebei Province, and established a 177-year floating tree-ring chronology of the cypress in the tomb.
