Guest post by Ellen Morris Bishop, photographer, writer, and geologist
As a geologist, I often travel through time. Show me a braided river channel, and I am standing on the banks of a Kaiparowits Plateau stream whose floods carried dinosaurs to their deaths 70 million years ago and left their carcasses as triumphant finds for today’s paleontologists.
My most ancient trips—back to the Precambrian, almost three billion years ago—occur amid the darkly-crinkled landscapes of biological crusts. On this time-travel odyssey, the sky is green, the sun a hazy dim vestige of itself. The crusts’ brittle mosaic is the only living cover on an otherwise barren land.
But now, the same landscape offers a shorter trip—back to the Cretaceous, the heyday of dinosaurs. For, amid the Grand Staircase-Escalante desert’s living crusts, and virtually indistinguishable from them, lie fossils of crusts that date to 80 million years ago.
Biological crusts’ dark pinnacles mantle the Escalante’s most arid landscapes in southern Utah. Archaic and primordial, plants without leaves, the crusts’ foundational cyanobacteria (aka: blue-green algae) are barely plants at all. The lichen and mosses that roof crusts’ firm surface are comparatively more advanced (they have vascular systems) but still primitive by evolutionary standards. Mosses and lichens have been around since at least the Silurian—about 475 million years ago. The cyanobacteria that carpet the desert surface are far more ancient. We can trace them back to the Archean—at least 2.8 billion, and maybe to 3.5 billion years go.
Without cyanobacterial biological crusts, the rest of life as we know it might never have developed. Cyanobacteria invented photosynthesis and, about 2.5 billion years ago, began to pump oxygen into Earth’s primitive, oxygen-poor atmosphere. Geologists call this the “Great Oxygenation Event”. It began a new geological era, the Proterozoic—or earliest life. Of all events in Earth’s history, this is perhaps the most important. Cyanobacteria introduced oxygen into the atmosphere, and ultimately, oxygen-based, life became dominant. The most humble of organisms literally paved the way for us.