Nothing can describe the ever-changing nature of our Planet better than rocks, like this limestone from the Dolomites, Italy, seen under a polarizing microscope. This was a sediment on a sandy beach of the Triassic - about 230 million years ago - with fragments of sponges, corals, and small gasteropods like the subject of the image. With time it became a solid rock, and with the continental collision and Alpine orogeny it was brought on top of a mountain peak. To become sand again...