The Millennium Tree is the cross section of a real redwood trunk that records over 1,000 years from the time it sprouted up through the 1930's. Paleontologists actually use tree rings and cross sections like this to do many things, not the least of which is discovering what our planet's climate was like over the past several thousand years. This is a study known as dendrochronology, where each ring on the tree represents one year of growth and that individual ring can tell us a lot about the climate and atmosphere at the time the tree formed. By comparing the thickness of the individual rings, scientists can tell us if the climate was warmer or cooler, or wetter vs dryer, that year compared to other years.
The rings also preserve the prehistoric atmosphere in the form of isotope data. Isotopes are different weights of various elements based on the number of neutrons that each element has. Many isotopes are unstable (radioactive), but there are many isotopes that are stable. Carbon for instance has two stable isotopes, Carbon-12 and Carbon-13. It also has several unstable isotopes, with the most prevalent one being Carbon-14. But the percentage of the different carbon isotopes is affected by the climate and this difference is then preserved in the tree as the tree builds up the woody plant matter in its trunk as it grows.
By comparing all that data for this tree to countless other trees across the globe, scientists are able to get a global view of the climate over time. They can also use the comparative thicknesses and isotope data in modern trees to line up older, already fallen trees, that they don't know when they were chopped down, such as in log cabins and other human settlements. The relative thicknesses of the rings forms a type of fingerprint that can be lined up with these older trees forming a continuous history of our climate that goes back much further in time than any tree living today is capable of. By understanding the isotopes and climate today, we can use that information to infer what the climate was in the past by the data preserved in these tree rings.
The Millennium Tree"Redwoods are ... ambassadors from another time"- John SteinbeckTravels with Charley (c. John Steinbeck 1962)Every tree has a tale to tell, and the tree's rings tell us its story. A California redwood grows by adding a new layer, or ring, of wood to its surface each year, so counting the rings reveals the tree's age. Written in the rings of this fallen tree are over 1,000 years of California history from 818 A.D., then it sprouted, to 1937 when it fell.