One of the mysteries of palaeontology is how footprints made by an animal hundreds of millions of years ago could ever survive long enough to be preserved as a fossil. When you walk along a beach, you leave some perfect footprints in the sand (so long as the sand is not too wet or too dry). But once a wave comes in, they're washed away. The eurypterids that have left their tracks in sandstone were probably staggering slowly across wet sand. At this time, more than 400 million years ago, few plants grew on land. There were no trees, no grass, not even any cauliflowers. This means that there was hardly any soil. Whenever the wind blew there would have been dust storms, the same as today when the wind blows across dry, newly ploughed fields. This very fine sand would have gently settled on the eurypterids' footprints, covering them up. When the sand eventually turned into rock, the footprints were preserved. Wind, rain and flowing rivers exposed the footprints for palaeontologists to find. Whenever I find one
I am always amazed I am looking at footprints showing the movement of an animal for perhaps one minute of its life, preserved like a snapshot for hundreds of millions of years.
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