Note: I do not have much experience with woodworking.
How is that wood can have a smooth texture with multiple "rings"? (I heard that trees the same number of concentric circle as their "age")
So how do producers make it wood so that it does not only have concentric circles, but smooth continous ones?
Image of the side of desk (the darkened top is just a shadow, the white is a piece of metal - I do not know why it is there):
I have taken a closer look with my eye (not on the image, but the physical desk) and do not see any discontinuities (no visible straight lines where multiple boards could be connected / glued together)