Tree Rings

From the book, Sequoia National Park, 1937.

Most school kids in California have probably seen a redwood tree section showing the annular rings on it with dates, like "WWII ends", "Columbus discovers America", "Jesus was born", dates like that.  So it's pretty common knowledge that trees can show years passing by the number and kind of rings they set down.

If you want to refresh your memory, here's the NOAA website that talks about tree rings. And here's the wikipedia article on dendrochronology.

Ok, so now you know all about that tree ring stuff.  Did you know that humans also have annular rings?


I didn't know this until recently when I stumbled across it accidentally.  For a project, I was looking for tree girdling pictures and just had to click on a cool dinosaur picture that came up. That led me to this blog "Sauropod Vertebra Picture of the Week (SV-POW!)".  The author talks about a discovery that his wife, Dr. Vicki Wedel, made about layers in our teeth.

Dr. Weidel found that there are
"two bands of cementum are laid down every year–a dark band in the winter (roughly October to March) and a light band in the summer (roughly April to September)"

Which makes us humans pretty tree-like if you see what I mean!  Not to mention helpful to the forensic scientists in the world.

Dr. Wedel's discovery is described here "Using tooth histology to help identify a murder victim in a 37-year-old cold case". 

Update with our ongoing drought...Thought I'd add this table I just ran across from the mid 1800's.

From W.O. Clark's "Ground-Water Resources of the Niles Cone and Adjacent Areas", Water Supply Paper, Issues 344-345, page 139.
You can find Clark's article on google books.