Writing in the journal Nature, Turner leaned on those recent discoveries to describe how the fossils may have formed when sponges, measuring a few millimeters to a centimeter across, became mineralized. The soft tissue was first to fossilize, encasing the 3-D network of collagen-like fibers that formed the sponge’s skeleton. Over time, these skeletal fibers decayed, leaving hollow tubules that filled up with calcite crystals.
