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Dating rings

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Ron Towner from the Laboratory of Tree-Ring Dating rings at the University of Arizona explains the principles behind dendrochronology and why this dating method is valuable to archaeologists.

Ron demonstrates how to accurately count tree-rings, and discusses the importance of patterns and master chronologies. Trees are often used to make analogies about the past. Family trees, the tree of life, getting back to your roots…. But beyond the powerful imagery that trees give us to represent our history, what can trees actually tell us about the past? Dendrochronology is the scientific method of tree-ring dating.

Americans first developed it in the early 20th Dating rings and now "dendro" is a common method of chronology that is used by scientists all over the world. Dendrochronology has become a fundamental tool in science, for reinforcing and expanding on the timelines of historical and ecological events in the past.

Dendrochronology operates on the principle that in temperate climates, like the southwestern United States, trees grow one ring every year. In the springtime when moisture surges, the cells of a tree expand quickly. Over the course of the summer as the ground becomes more dry, Dating rings cells begin to shrink. This change in cell size is visible in tree-rings, or growth-rings. Dating rings variation in ring width is based on the amount "Dating rings" water a tree absorbed in a given year.

Rainier years are marked by wider rings, drier years by narrow ones. Dating rings, dendrochronology in its simplest form is a matter of counting rings. But, it's not always Dating rings simple.

Natural tree variation, sudden climate changes However, counting alone does not tell dendrochronologists what time period the tree is from. To find that out, scientists must focus on the pattern of rings rather than number of them.

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Say you walk into an old forest and you find the stump of a thousand year old tree, explains Towner. Say you also find a piece of wood from a different tree in that same forest, and it has rings on it. If you were to lay a cross section of that wood on top of the Dating rings stump, you would find that somewhere inside the rings of the older tree, of them would match the Dating rings of the piece from the younger tree.

In other words, tree rings develop in the same pattern e. If it rains a lot in that old forest mentioned earlier, then all of the trees get lots of water and all of them grow a wider ring that year.

Summer Dating rings all of the affected trees show a narrower ring. But, tree ring patterns never repeat themselves either, which is what makes them identifiable in time and place. Dendrochronologists identify these patterns by laying a strip of graph paper across a sample, and marking only the narrow rings.

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