Which growth rings are older and why: those that are closer to the bark, or those that are closer to the wood. Why?

Tree rings are formed every spring. They consist of storage cells where certain organic nutrients are stored, and they also consist of conductive tubes: sieve and vessels. New rings are formed on top of the old ones, that is, closer to the bark. The tree trunk expands with the outer layers rather than expanding with the inner thickening. In this case, the barrel would simply crack due to the strong pressure inside. If you look at the trunk cut, you can see that the outer layers are younger than the inner ones.