As animals, and especially visual animals at that, we have a particular experience of the light. For us it is illumination, information about our surroundings. For that purpose moonlight or even starlight will do. And for tens of millions of years, that’s all we ever saw. Somehow a few of us made it through the Permian extinction, and into the Triassic, but the ascendancy of the dinosaurs eventually forced us into the darkness of the night. Our world became dim, and our eyes went colorblind. Most mammals today see only two colors, but a few of us have re-evolved a third photoreceptor. Three colors is still inferior to the four or five or six seen by many near-surface fish, birds, reptiles, insects, and other arthropods. The stomatopods are almost biological spectroscopic imaging systems, with 12 color channels in each of their independently movable trinocular eyes. We are lesser than the eyes that never left the light. They stole the colors from us and made us hide within the night. They kept the sun for themselves, not knowing that our small and furtive ways, our burning endothermy and our fur would see us through the aftermath of the KT impact.
More universally, nearly all earthlings experience the light as the ultimate source of our sustaining energy, the fuel with which we stave off chaos for a little while, and for that purpose, the pale moon and distant stars will not do. One can see in the night, but food doesn’t grow there. We could only live through those long dark ages because on the far side of the world, the sun was shining. Today I think some of us forget this fact, because we have become so visual as a species, and so distant from the phototrophs that gather our light. Maybe in this way we’re not so different from the early mammals, who scuttled and climbed in the moonlight, like tenrecs and tree shrews, ignorant of their thermonuclear benefactor.
Almost all our energy comes from the sun: coal, oil, gas, hydro, wind, solar (obviously), biomass, waves. Even nuclear energy, whether fissile or in the form of geothermal heat is all still ultimately attributable to the stars, to their energetic and transmutational deaths. Only the tiniest fraction of the energy available to life here comes directly from some non-stellar source: tides (still half solar), and the heat of differentiation left over from when our planet’s interior stratified. Given this, if I had to choose something to direct worshipful attention toward, it would certainly be stars, and our star in particular.
It seems bizarre, but despite the enormous energy transmitted by these gifts of light that we recieve, and our global focus on energy sources: clean, dirty, past, and future, it turns out that we do not as a planet, as a biosphere, consume energy at all. As long as the planet is in thermal equilibrium, and we are neither sequestering our incident sun chemically, or releasing ancient light in the form of fossil fuels, the amount of energy we re-radiate to space exactly balances that which falls to us each day. And those caveats are minor. Human civilization today uses about 15 terawatts of power. The power of the sunlight incident on the Earth is more than 10,000 times as large. All the fossil fuels buried over geologic time, and bequeathed to us for better or for worse, represent, in total, no more than a few months worth of accumulated direct sunlight. The total amount of energy that would be required to transform the Earth into a Cytherian hell is likewise small, compared to the solar flux. The vast majority of the light that falls on Earth is simply sent back into space as heat. Our atmosphere keeps us a little warmer than a pure black body, but that doesn’t change the overall energy balance. What comes in goes right back out. A miniscule portion of that energy passes through us, through life on Earth, before it is returned to space, and in passing it maintains us.
It turns out that what the biosphere consumes is not energy; what a world needs to live, is order. The difference between the light we get and the light we give is entropy. Light from the sun is high quality energy. The rays are nearly parallel; the energy per photon is large on average. The light (infrared) we return to space has been degraded: 300°K, and isotropically distributed. Most of that degradation is physical, not chemical or biological (it happens on Venus, Mars, and Titan too), but a tiny fraction of that disorder is there because of us. It’s there because we live. Life at its most basic and universal is complexity. It’s the persistence of information, in a barely controlled seething chaos. Biospheres eat order, and excrete anarchy.
Eventually entropy wins, but not yet.