A couple of years ago we spent a week at Death Valley. It’s a place of extreme landscape beauty. But there are many surprises to be found just by picking up a rock. The three examples I show here tell a complicated story of evolutionary history past and present.
This rock has a “desert glaze,” which is actually a large bacterial colony. The bacteria have built themselves a barrier, something like the plaque on your teeth. Underneath this protective barrier they carry on their submicroscopic life activities.
This rock might see an inch or two of rain per year, but it’s just enough to sustain extremely slow-growing lichen colonies. Similar to the bacterial colonies on the rock above, these lichens carry on their metabolic processes at a very slow rate, performing photosynthesis only when there is adequate dew or precipitation in the atmosphere.
The rock below tells a story of Earth History that’s billions of years old. When photosynthesis evolved free oxygen, a byproduct of the photosynthetic process, became abundant on Earth. Iron-rich ocean rocks like this one absorbed the oxygen and rusted. Eons later the rocks at the ocean bottom were lifted to the surface where we see evidence of the “oxygen revolution” now.