Some open rocky places on the ravine's trails appear lifeless from repeated trodding, but scraggly black stuff is gathered here and there. I like to call it instant algae because, after a few minutes in a glass of water, it turns green and emits oxygen bubbles. It is nostoc, slippery and photosynthetic after rain, not a true alga, a plant, but more closely related to the first bacteria that invented oxygen manufacture by photosynthesis using water and carbon dioxide about four billion years ago. Nostoc's ancestors totally transformed the Biosphere, making our green terrestrial world a familiar way of life.

Nostoc's harsh environment reminds me that life was more difficult and totally aquatic before bacteria and algae made oxygen, some of which was ionized and became an atmospheric ozone shield against damaging (mutagenic) ultraviolet radiation. Before then no life could live on land. It was just too dangerous. Are we returning to those days? Holes in the ozone layer over Arctic and Antarctic regions are growing, caused by chlorofluorocarbon gases wasted from our spray cans and air conditioners. And human skin cancer increases accordingly, especially in near-hole places like New Zealand, where I personally felt the message.