These crusts play an important role in the ecosystems in which they occur. Cyanobacteria, previously called blue-green algae, are one of the oldest known life forms. It is thought that these organisms were among the first land colonizers of the earth's early land masses, and played an integral role in the formation and stabilization of the earth's early soils. The earliest cyanobacteria fossils found are called stromatolites, which date back more than 3.5 billion years. Extremely thick mats of these organisms converted the earth's original carbon dioxide-rich atmosphere into one rich in oxygen and capable of sustaining life.
Cyanobacteria occur as single cells or as filaments.
The most common form found in Colorado Plateau soils are the filamentous type, which are usually surrounded by sticky mucilaginous sheaths. The sheaths have other functions as well. When moistened, they swell up to ten times their dry size. This ability to intercept and store water benefits both the crustal organisms as well as vascular plants, especially in arid regions with sporadic rainfall. Sheaths, and the organisms they surround, also contribute organic matter and help make essential nutrients available to vascular plants.