Shedding Light on Life
For the natural world, the sun nourishes, regulates, warms and more; no wonder scientists still find flashes of insight in its rays
They come from the sun and from hot tropical seas and then drum on our roofs encased in water or drift into our yards at the heart of snowflakes. Products of the vital interplay between solar light and earthly life, they are the weathermakers - the solid nucleii required for moisture to condense and form a drop, and, in combination with billions of others, to form a cloud. They came into being a month ago, maybe more, far from our yards and in form very different from the cold kernels of sulfate that will seep into our soil come the first thaw.
They were born as breaths of protest from the sea life that periodically gets too hot under the baking equatorial sun. Overstimulated, the teeming soup of phytoplanktonic organisms-mostly larval fishes and crustaceans, protozoans and plants-begin to congest, starve and suffocate in the heat. Not all of them can do anything about it. But among the algae in the soup are the coccolithophorids, tiny sea-green plants that can actually manipulate the weather in order to save themselves.
As the water warms, the coccolithophorids give off dimethylsulfide, a gaseous chemical. "As it rises from the water into the atmosphere," says Joseph Ramus, a photosynthetic physiologist with the Duke University Marine Laboratory, "the gas oxidizes into a solid sulfate, which becomes the nucleus of a raindrop."
The result? A cloud cover that blocks the sun, cools the sea and brakes the phytoplanktonic procreation rate. There is no mass die-off. The soothed, drifting life simply slows down-at least until the clouds move on to become someone else's summer rain or Christmas snow and the equatorial cloudmaking cycle begins again.
Some researchers suspect that most of Earth's rain and snow originate during such processes. "We're not yet certain, but there's a lot of current research aimed at finding out," says Ramus. "In the meantime, it has been a stunning realization to learn that phytoplankton may literally manipulate the weather to ensure its own survival.
"But," he adds, "we are becoming less surprised at such revelations. Each is just one more way among the countless, intricate and marvelous ways we are discovering through which the sun's energy is absorbed and released as the driving force of life on Earth."
We humans are so basically creatures of light that we define our natures by it-or by its lack. Our moods are sunny or black, our minds bright or dim. If we don't understand, we're in the dark; but when we begin to comprehend, the light goes on; we get a glimmer. At our best, we are each others' sunshines; and in that state our eyes gleam, our faces beam, our voices glow, our conversations shed light; we are bright, radiant and lustrous, with occasional flashes of inspiration, streaks of brilliance and blazes of glory.
Light is intricately and inextricably woven into the fabric of life beyond our own as well. From the sun comes all earthly energy; and through photosynthesis, all food. In amoeba and in man, the sun fixes an inner compass, powers penchants and passions, and encodes both single cell and cerebrum with so many timing devices that the researcher's common phrase biological clock might more appropriately be biological sundial. The circadian rhythms within all life (circadian meaning, literally, about a day) are synchronized to that same cycling of solar light that determines when lupines germinate, mayflies metamorphose, robins breed, snowshoe hares change color and sleeping bears wake.
It happens daily, at all seasons, everywhere.
In our gardens, as winter fades, the bean aphid will lay eggs to hatch later-until the day length reaches exactly 14 hours and 55 minutes, when it will start giving birth to live offspring to take advantage of the warmth.
In the same season, as the salmon turns shoreward to hunt among the burgeoning life in warmer, shallower waters, the sun will warm a pineal gland at the top of the fish's pate, stimulating an overproduction by the pituitary gland that triggers its urge to return to the waters of its birth and to spawn.
The musk-ox will shed its insular undercoat, the mallard its winter down, the snake its skin, all in synchrony to the lengthening day. While at sea, in single-cell plants that have no winter insulation to shed, a rotating chloroplast will turn gradually away from or toward the sun, matching the amount of energy it receives to the amount it needs.
More than half of all light energy utilized on Earth is photosynthesized by algae such as those coccolithophorids responsible for stimulating cloud formation at sea. Most of the other half is processed by plants in order to feed themselves and, indirectly, to feed every other living organism. "Physiologically speaking," wrote the late horticultural scientist Eugene Rabinowich, "all the animals on land and in the sea, including man, are but a small brood of parasites living off the great body of the plant kingdom. If plants could express themselves, they would probably have the same low opinion of animals as we have of fleas and tapeworms."
Animals tend to use sunlight more functionally-for navigation, stimulation or communication. The most familiar examples, of course, involve vision-the messages organisms receive by absorbing reflected light through specialized photoreceptor cells. As do most eyed organisms, we rely on vision far more than we do on any other sense. It is because of vision that flowers have evolved colors far into the ultraviolet ranges (beyond anything we humans can see) in order to attract the birds and insects that can detect them.
And vision is what orients the queen bee and her pursuing drone suitors during the skyward spiral of the mating flight. Because of that flight, apiarists through time were not able to control the mating of domesticated bees-until last year, when Oregon State University researchers Phil Rossignol and Lynn Royce discovered in developing the world's first bee mating chamber that they could fool the drones into approaching a queen by suspending her highness in a dome lit by a simulated sun.
Pit vipers such as the various species of North American rattlesnake actually have two sets of eyes-one lensed pair that we recognize as similar to our own, plus a pair of membraneous sensors in the "pits" between the nose and eyes. Through these sensors, the snakes can literally see the heat-generated, infraredimages of birds, small mammals and other prey.
And then there are those relatively few bioluminescent creatures which-through a process nine times more efficient than a light bulb-can actually store sunlight and reemit it later. Among them, the black dragonfish is doubly awesome: Through its eyes it projects red light that other fishes can't see, enabling it to stalk its prey unseen in the abyssal dark.
For all of our identification with, and dependence upon, light we have through human history taken it mostly for granted, tending to notice the sun most in its absence. Scientifically, we have focused less on how life is energized by light than on how various organisms compensate when the light is turned down or off. We've learned precisely how, for example, as days darken toward winter, a broad-leaf tree adjusts the energy conversion within its leaves by growing strips of cork cells that gradually constrict the water flow at the junctures of leaves and twigs at a rate to match the weakening light. As the photoperiods of seasonal light dwindle, the chlorophyll disappears, leaving the reds and yellows, the oranges and the purples, of pigments no longer hidden by the dominant green.
We've learned, too, how life can remain true to the sun even when it isn't shined upon. The diminutive fruitfly, for example, invariably sheds its pupal husk an hour before dawn even if kept in total darkness-a rite evolved, it seems, to take advantage of the highest relative humidity of the day so that the new adult can swell, shape and harden its skin before sun-dried air can suck away its supply of moisture.
Twilight-the level of light just before dawn and just after sunset-functions as the on-and-off switch for the fruitfly, and for much of the rest of the natural world, including ourselves. As sunlight rises or drops to twilight intensity, the photochemistry between light and living cells correspondingly changes and issues new orders: At dusk the poppy folds its petals; the hummingbird slips into torpor; the human sleeps.
And the resulting rest is well and good-unless the light is gone too long, in which case the petals open faithfully to a darkness that will starve them; the tiny bird exhausts its energy reserves and slips from torpor toward death; and the human . . . "Well, we're just beginning to learn how too much darkness or not enough light-affects our bodies and our brains," says Al Lewy, whose pioneering work on seasonal affective disorders (SAD) at the Oregon Health Sciences University in the early 1980s demonstrated that phototherapy can alleviate winter depression and jet lag.
Both maladies-with symptoms ranging from slight disorientation and weariness in jet lag to listlessness, chronic fatigue and even suicidal depression in severe cases of SAD-are results of our circadian rhythms being jarred out of synch. The jet deposits us in a time zone with twilights several hours different from our own. To light-starved bodies and minds, the winter night comes too often and stays too long. Lewy and co-workers found that in many cases, the resulting disorders are treatable with photic antidepressants-special, sun-simulating lights that fool the body into behaving as though the twilight switches are being flipped to a saner and more nurturing rhythm.
It is only in the past decade that we have turned our research attention less to exploring how life compensates for darkness and more to the myriad subtle ways in which Earth's plants and animals-again, including ourselves-store and use light from the sun.
"I don't know why, as scientists, we shied away from the sun for so long," says Duke University's Ramus, who used to focus his attention on how deep-sea plant life compensated for a lack of light. In the late 1970s and early 1980s, Ramus and his colleagues discovered some plants in the light-poor depths that had evolved fiber optics to increase their light-catching surface "in order to suck up every photon that comes their way" Others, he found, had rotating chloroplasts within their cells that could turn toward or away from sunlight depending on their need for more energy or less.
"We discovered some amazing adaptations; but we had pretty much exhausted our avenues of research when we were struck by the obvious: We were working in the photic basement, where life grasps at straws. Why not shift to the ceiling, where the energy level is a millionfold and where life adapts to light so much more dynamically, and in so many more ways?
Ramus and other researchers quickly began to appreciate the interlacing of light and life where the two meet at levels of high intensity. The systems they found among light-basking organisms have ranged from the rainmaking equatorial phytoplankton to weeds that survive heat so sweltering it would kill most plants. In the North Atlantic's 2million-square-mile Sargasso Sea, the weeds beat the high temperatures by lighting up the sea with massive, bioluminescent "energy dumps" at night.
Until this recent work, Joseph Ramus and thousands of other scientists have looked at ways in which other organisms accommodate darkness and cold in hopes of dealing more effectively with the handicaps we are dealt by weak light and winter. But the urgencies have shifted, lately, to the sunny hours. We are beset by pressing questions: How is destruction of oxygen-manufacturing forests affecting our air? What are the disease and greenhouse-effect dangers posed by the dwindling ozone layer and a corresponding increase in ultraviolet radiation?
The sun fuels the system, and by some measures we humans are over-exploiting its resources. Whereas our ancestors needed about 2,000 calories a day to subsist, we now consume about a quarter of a million. Without the means to manufacture that kind of energy within ourselves, we have turned to the sun-derived energies within fossil and other fuels. And we're using that energy several million times faster than it was stored.
We now know that we are as much creatures of light as are the maple, the viper, the algae. In our relationship to the sun may lie the keys to a healthy Earth. One of the more eloquent ways of getting at the same idea comes from British atmospheric scientist James Lovelock; popularizer of the Gaia theory (named for the Greek goddess of Earth) that the Earth is one huge living organism. According to Lovelock, there's a crucial lesson for humanity in nature's usual harmony-"taking the chaotic flow of energy coming in from the sun and turning it into coherence."
From chaos to coherence: To the energy problems that cloud our life on Earth, that goal could be the silver lining.
Oregon writer Grant Sims contemplated the extremes of light and dark during a decade in Alaska. His book Leaving Alaska (Atlantic Monthly Press) is due out in the spring.
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