Dendrochronology is a type of tree ring dating that is done by evaluating the patterns of rings on a tree trunk. These rings, known as growth rings occur as a tree grows and matures. A ring is added each year as the vascular cambium cells of the tree grow and proliferate. During years where sunlight and water are plentiful, the rings may be larger demonstrating a lot of growth. During years of ecological strife or drought, the rings are smaller. The newest rings are found closest to the bark layer (outer layer) of the tree. These rings are most prevalent in temperate forest biomes, where there is ample time for trees to grow in spring and summer.
The cross section of a tree trunk can be analyzed by counting the rings that form from the growth of the vascular cambium. Each successive ring equals one year in the life of that particular tree. As the vascular cambium grows in spring and summer a large portion is grown. The larger portion of the ring is formed by secondary xylem, the thin layer is formed by secondary phloem. The rings reveal the passage of time for most species of trees. This can be used to give approximate dates of the trees to the year.
The analysis of tree rings can have many applications in the world of science. The first, eluded to earlier, deals with climate factors in the history of Earth. The rings of a tree grow best in the most favorable conditions for plants; warm, sunny and with ample water. Any deviation from this will not give the tree the best opportunity to grow. In extraordinarily large trees can reveal a lot about climate changes and weather during a long time interval. If a tree has very tiny ring patterns for a number of years that will indicate a very hot and dry climate for that period.
Tree rings can also be used in the field of archaeology. Scientists can create tree ring sequences to use to compare samples of artifacts and structures that are comprised of wood. The pattern and type of wood can reveal the time period by which the item is dated to. This type of dating is often used side by side with radiocarbon dating to ascertain the age of the wood. This can be very useful to an archaeologist who needs to confirm radiocarbon dating with another source. At present, there is a scientific database to date back tree rings to 11,000 years. However, most trees can only reveal a few hundred years of data.