text:  Every tree has a set of rings in its wood, one for each year of growth. While helpful for figuring out how old a specific tree is, some scientists are using these patterns to reveal the history of our planet. And here to decode what tree rings can tell us about our past is Valerie Truet, professor in the Laboratory of Tree Ring Research at the University of Arizona and author of the book Tree Story, The History of the World Written in Rings. Welcome.