RARITY

Discovering the rare Fossombronia liverwort this week set me to thinking about the concept of rareness itself.

A species can be rare for several reasons. For example, maybe its adaptations equip it for living only in very unusual habitats, as was the case with our limey-muck-loving Fossombronia, or maybe the species is losing out to aggressive weeds. It's thought that over 99.9% of all species that ever lived on Earth now are extinct, so at one time or another all species are rare. In Nature, "commonness" is unsustainable, and even "rarity" trends toward extinction simply because any rare thing is relatively easy to dispose of, as when a bulldozer destroys a species' last refuge.

Over time, the Earth's landmasses shift about, ocean currents alter direction, solar radiation varies in strength, the atmosphere's combination of gases changes... so the planet's mix of species constantly evolves accommodating and building on not only these changes but also newly evolved adaptations: scales on the first fishes; warm bloodedness among the mammals, and; primates with their big brains. In fact, the only process in the living component of Nature that looks like it might be permanent and sustainable is evolution, and even that ends when there's nothing left to evolve.

One morning this week my friend Ron dropped by buzzing with insight after viewing a program in which someone made the point that if the Earth were to be represented by a golf ball, a model of the big star Canis Majoris built at the same scale would be the height of Mt. Everest. And to fill Canis Majoris's model with Earth-representing golf balls, you'd need enough to cover the entire state of Texas 22 inches deep (56cm). If my math is correct, that means that New York State would be beneath 8½ feet (2.6m), and little Delaware 198 feet (60m) of golf balls.

And there are lots of stars other than Canis Majoris. Current thought is that their count probably is more than the number "one" followed by 24 zeros -- a septillion stars.

When Ron left I leaned on my shovel awhile letting things digest, because before his visit that morning I'd been thinking about the Fossombronia liverwort's "rareness." Now as I stood there with morning sunlight from one among billions of stars feeling good on my skin and a fresh Earthly breeze blowing up the canyon carrying the scent of fresh soil and warming junipers, I saw that in terms of the inconceivably huge Universe, the Earth itself is rare. And with the ephemeral nature of species, Earth's living things are doubly rare, in fact so rare that it's hard for the human mind to grasp how precious, vulnerable and evanescent the planet's living things really are. And that's not even considering the individuals of which species are made. Compared to the Universe and its time scale, we living things are hardly flickers of presence.

What does it mean to be in a Universe and on an Earth where everything, everything, is so special and worthy of notice?  .