So here we are, 43 days past the winter solstice and already picking up a few more minutes of daylight every day, measurably creeping closer to spring.
Today we mostly think of “sun worshipers” as misguided individuals in pursuit of the kind of tan that modern medicine tells us is bad for us in the long run. I actually think that the more literal kind of sun worship that took hold of civilizations from ancient Egypt onward was more sophisticated than we 21st-century skeptics might think.
It is quite scientifically true that life on Earth depends entirely on the sun, that big ball of nuclear fire in the sky. Earth just happens to be in the “Goldilocks zone,” neither too close nor too far away from a suitable star.
A planet twice as far away would get only one-quarter the light and warmth, and one half the distance would get four times as much, spending their cosmic lives in either ice or fire. Space probes have shown us that desert-like Mars, a little too far out there, has at best vestigial polar ice caps, while Venus, a little too close, is a swirling cauldron of hot gases.
Taking the long view, Earth started out as a battered rock without an atmosphere and will end up a cinder fried by the expansion (a few billion years from now) of the dying sun. But meanwhile, here we are, on the third rock from the sun, living in that beneficent “window of opportunity” — a period of roughly eight billion years when conditions will support a biosphere fueled by a star in the prime of its life.
We are, as Michael Gross points out in his entertaining book “Light and Life” (Oxford University Press, 2002) in the right place at the right time, more or less at the midpoint of viability. Earth “has a fair chance of sustaining diverse life for another four billion years, as long as we humans don’t do anything too silly,” he points out in a fairly comforting way.
The Copernican revolution — attacked as blasphemy — was correct in putting the sun, not the Earth, at the center of our little solar system. Now that we’ve gotten around to measuring such things precisely, we understand that Earth and its fellow planets are “mere peanuts,” in Gross’ words, with the sun representing 99.9 percent of the system’s total mass.
But no revolution has made more of an impact on the fate of the planet than photosynthesis, that process invented by the plants that forged a direct link between the sun’s energy and chemical energy that could sustain life. It changed the planet forever.
It is the plants, through the complex mechanics of photosynthesis, that produce the oxygen we breathe, absorb the carbon dioxide we can’t and keep the atmospheric gases in balance. It is the plants down there at the base of the food chain, producing foods from microscopic fungi to grass to artichokes that animals like us can eat.
Nearly all of the abundant life we see around us is directly or indirectly dependent on just these two things: sunlight and photosynthesis. The exception are those deep sea creatures living near hydrothermal plumes that developed an alternate food chain based on sulfur compounds — tube worms, for instance.
Tube worms haven’t gotten very far in life, though. Stationary like plants, they live a modest (some would say boring) life in perpetual darkness. They don’t celebrate any special occasions, as far as we know, and never go to the mall.
Plants, while equally lacking eyes, definitely “see” the light, sensing, growing and bending toward it in deliberate movements we call phototropism. You can observe this in the way a sunflower turns throughout the day so it always faces the sun.
The importance of tracking the sun’s cycles through the seasons was crucial to the development of agriculture, the management of plants for our particular preferences. It also spawned early religions, with the Egyptians, the Incas and the Celts who built Stonehenge all putting the sun at the center of things cosmological. Makes more sense to me than many modern religions, with their angry, jealous patriarchs, implacable gods and “holy” wars.
Today we have accurate calendars and timepieces that let us be casual about sun cycles, seasons, solstices and equinoxes. We don’t think very seriously or very often about how it would be if the sun didn’t “rise” and the plants dependent on light expired, leaving us breathless.
We’re okay — for now and the foreseeable future, so we have the luxury of expecting things to continue much as they have. Lucky us.