3rd Rock

Why is our planet named Earth? It privileges the most solid-like elemental phase of matter. The solid ground is where most of us live, even though Water covers the majority of our planetary surface. Air seems ethereal and transient; we might not see it but our bodies would notice its absence in our dying gasps for breath.

Earth has the connotation of soil – fertile in giving rise to flora. But increasingly short in supply. As the world’s population congregates in cities with pavements, roads, and high-rise buildings, our experience of Earth is less and less earthlike.

According to Wikipedia, Earth comes from the Anglo-Saxon erda referring to the soil. And perhaps that is how our planet got its name. Interestingly, the other planets in our solar system are named after gods, Greek and Roman, but this is a reflection of particular histories of language and culture. Other nations speaking other languages had different names carry connotations of deity and life. Gaia, the Greek goddess, has inspired the scientific hypothesis that our planet is like a single organism.

Carl Sagan called our planet the Pale Blue Dot, inspired by extraterrestrial photos from the Voyager spacecraft. TV aliens might call it “3rd Rock from the Sun”, it’s rocky-ness distinguishing it from the larger gas giants in our solar system. Today we search the astronomical skies for Earth-like cousins. There are many. We don’t know if they are pale blue, but we analyze lower frequency waves looking for bio-signatures, clues that we might not be the only living beings in the vastness of space. Oxygen, Methane, Nitrous; perhaps in a distribution out of equilibrium indicating an atmosphere coupled to a biosphere. But what we see now was light-years ago. What was once alive might now be dead. Or in equilibrium.

Persistence is a funny thing. Could it be exhibited differently in the living and the non-living? We think of rocks as persistent things, but not alive. In The Origin and Nature of Life on Earth, Eric Smith and Harold Morowitz make the interesting suggestion: “In abiotic geospheres, durable patterns are maintained because they are realized in durable entities. The dynamic order of life shows the opposite pattern: durable patterns are realized on transient entities – the core metabolites. Yet this dynamical order is arguably the oldest fossil on earth.”

The same small subset of molecules shows up again and again, appearing and disappearing in cycles of chemical reactions. It’s a different kind of persistence that makes this 3rd rock more than just a pale blue dot.