One of the (copious) reasons I adore swimming through “just wet rocks” is the abundance of fossils. Sure, we don’t see a ton of dinosaur fossils. But there are denizens of corals and shells of marine creatures that once created and made up what was once ancient coral reef. In Florida there are places where you can see the vertebrae of a whale that sank to the seabed millions of years ago and was subsumed by the reef sticking out of the walls. Here in Mexico there are piles of bones of long extinct creatures like the gomphotherium or the megalonyx. It is impossible to not be swept up by awe or cowed by inconsequence in the face of such spans. Looking beyond the formation of the caves or the speleothems, to recognise and to appreciate the long, plodding workings of biology recorded in stone is to venerate unfathomable time and our place within it. Consider that whales are descended from some sort of wolf-like creature; but sea lions come from something more like a bear. It was only ~4 million years ago that the genera Pan and Homo branched from one another; we still share about 99% of our DNA with chimps (though we also share about 50% of our DNA with mushrooms, which goes a long way towards explaining a great deal about humanity). Then there is research as in THIS article, which suggests that the animals we were trained since grade school to think of as terrible lizards were - probably - more like giant, killer pheasants. Toothy, death chickens. Murder mynas. Terrorkeets. Probably. To the best of our knowledge today. And even that tantalises the imagination and sense of wonder. For all the fact that we’ve got a fossil record that illustrates billions of years, the parts of it we do know are vastly outweighed by the parts we don’t. And almost certainly never will for sure. So we’re stuck imagining a T.Rex covered in brightly-coloured plumage like the biggest, scariest turkey ever. Or we can float over the complete skeleton of a ground sloth mourning the moment tens of thousands of years ago where the poor creature finally succumbed to thirst and exhaustion in the endless darkness, laid down, and died. In the Rose Center of the Museum of Natural History in NYC there is a spiralling exit walkway out of the planetarium. It’s 360 feet long with a scaled timeline on the outer rail of the 13 billion year history of the universe. Every average stride down crosses more than 100 million years. At the bottom, at the end of the timeline, just before you step off the walkway onto the main display floor, there is a single human hair embedded in acrylic. The width of that hair represents the entire history of our species. I was just a kid when I first stared at that hair. The sense of astonishment and humility has never left me; for me it rides on the wind through the trees and effervesces with the twinkling of every star, always in the background reminding me that time is diminishingly short and bloody well better make the best of it. But to swim through a place where the walls are spangled with innumerable fossils of millions of creatures that went about their little lives millions of years ago… it replenishes that sense. Refreshes it so deeply that to surface afterwards is almost to feel reborn to the world we’re lucky enough to get to enjoy for the duration of our little lives. With a deep gratitude that I don’t ever need to run away from a Spinosaurus whether it had feathers or not.