Oldest Life on Earth

THE OLDEST LIFE IN THE WORLD

Not long ago we were told the redwoods were the world's oldest living things. Then science nominated the bristlecone pines. Now yet another plant is singled out for superlative age: the lowly creosote bush. Although a utilitarian shrub for humans for centuries, it is not held in high esteem by moderns. Yet some creosote bush specimens may be 11,700 years old!

Eleven millenniums or so ago, as the pervasive chill of the last Ice Age ebbed, the seeds of the desert were sown. Mystery still shrouds their odyssey. Perhaps the winds wafted them or birds brought them into that place and time of transformation. How they arrived no one knows.

As the world warmed, though, so did the face of the land. Piñons, junipers, and other cool-country trees, which had invested much of what now is our continent's desert, retreated to the uplands.

Scientists have learned this from the nearly indestructible nests of pack rats that lived there then. Remnants of the vanished forests remain locked to this day in the legacy of the little rodents.

Some of the alien plants must have been driven out as the soil warmed and water virtually vanished. Others, over the centuries, developed incredible survival strategies. None of the very specialized newcomers homesteaded more tenaciously than the creosote bush, climaxing a journey that started in the deserts of South America thousands of years earlier. Today, that lacy, drab-olive shrub with shiny leaves-and tiny but bright yellow flowers-is the most obviously commonplace plant to be found across the lowland southwestern United States and northwestern Mexico. From the depths of California's Death Valley, below sea level, to the Big Bend of the Rio Grande, in Texas, they are all but inescapable.

After a summer storm in the Sonoran Desert of southern Arizona, the ubiquitous bushes infuse the air with the faintly acrid scent that brought about a misnomer. Creosote bushes have nothing to do with the chemical creosote, distilled from wood or coal tar. Hediodilla, the Mexicans call them, or literally "little stinker." It is an odor many of us find soothing, like the saltiness of the seashore, rather than unpleasant.

Still, those somewhat heart-shaped shrubs thrive by the billions. Each is a miniature oasis sustaining a chain of life unlike any other. They harbor insects that could not continue without them.

Because creosotes are so prevalent, they tend to provoke boredom among some people. A botanist named Frank Vasek once was one of them. When he first encountered them in 1950, as he drove across the Mohave Desert in California, he was struck by their sameness. For years, he conceded not long ago, "I looked upon creosote bush as something that was just there, filling in desert space between the times and places when the 'real' desert plants put on a show of flowers." His decades of research at the University of California at Riverside produced a profound change of attitude. That was fortunate. Dr. Vasek discovered a few years ago a circle of creosote bushes -cloned from a single seed-which he defends as the oldest living thing on Earth.

Unlike Dr. Vasek, microbiologist Emilio Mora grew up in southern New Mexico among the creosote of the Chihuahuan Desert. He was reared on the conviction of Indians and his Mexican-American neighbors that the plant possesses curative powers. That too, was fortunate.

Dr. Mora now has found, years later, that an extract from the shrub-known to science as Larrea tridentata-kills cancer cells in test tubes. His laboratory at Auburn University in Alabama is assay-ing the extract as a curative of tumors in laboratory animals.

Perhaps this disease-fighting broth, and almost certainly Vasek's ancient clone, are consequences of Larrea's reactions to stress. Stress is what makes a desert a desert. When blowing sand all but buries them, the bushes resist. Often in the Algodones Dunes, west of Yuma, Arizona, only the top few inches of the branches show themselves. They stand resolutely where rainfall rarely exceeds a few inches a year. If there are years without rainfall, they still cling tenuously to life. They persist even in North America's most rain-less reach in the Gran Desierto at the mouth of the Gulf of California. They seldom rise more than a foot and a half on that parched plain, however, about one-fourth their usual height.

Creosotebush (Larrea tridentata)

This remarkable yet often overlooked shrub is a dominant species in all but one of the North American deserts. Several ploys, at least one of them peculiar, permit creosote bushes to survive in settings so dry. As with much of the desert flora, a waxy coating on the leaves conserves water by slowing evaporation. To capture every drop, the roots plumb deep into the ground and spider-web outward just beneath the surface. Certain other plants, notably ocotillos, simply shed all their leaves when drought descends. Creosote bushes change covers. They doff their familiar foliage, then grow a tougher, drier canopy as much as two-thirds smaller than the quarter-inch-long leaves that were lost. This new growth still can feed itself-produce food by photosynthesis-even after drought has dissipated half its weight in water. The leaf cells are so small they need not shrink in response to extreme aridity, as leaf cells generally do. And when more moist conditions return, the shrub is ready for renewal.

CREOSOTE

Vasek, the botanist, believes it was precisely such a pattern that caused his clone to grow in circles. That notion entered his thinking early in the 1970s when he was cataloging vegetation in one part of the Mohave. "I noticed that the creosote bushes grew in large clumps and that each clump had numerous stems at approximately ground level," he remembers. "The question arose as to whether these clumps were derived from multiple seedlings or from a type of vegetative spreading from one initial seedling.

Although the latter turned out to be true, Vasek was not to learn that for some time. For several years, in fact, he devoted little thought to the possibility. Then he and other scientists visited a scene increasingly and unfortunately common in the sunbaked Southwest: a swath of desert where off-road vehicles had ground the vegetation into oblivion. A reporter with them wanted to know how old the creosote bushes there were. To the botanist, the question was troubling and intriguing. "I started to answer that they must be about 300 to 400 years old," he says, "when it suddenly dawned on me we simply did not know."

He knows now. The newsman's question launched him on an intensive quest. Vasek located more Mohave locales where creosote bushes appear in circles, ragged ellipses, radiating outward from a bare center. He compares the fringes of these rings to "the outer layer of living bark on a redwood tree. The inside wood has long since rotted away. The entire distance to the center of the creosote ring was at one time solid plant matter. Thecreosote bush starts with a center stem and grows outward, with the inside dying and rotting away, and the circle keeps getting bigger and bigger."

One of the biggest he found, 150 miles northeast of Los Angeles, measured seventy feet long by twenty-five feet wide. It has since been named King Clone. Chemical studies showed the clusters of King Clone, instead of individual plants, were genetically identical, an outgrowth of an original bush. Samples from the stillgreen outer edge were estimated to be 100 to 150 years old. But old wood specimens nearby were radiocarbon-dated at 540 years. By determining the rate at which creosote bush spreads across the surface in that locale, Vasek calculated the time when King Clone took root: 11,700 years ago. Thus, the King would be three times as old as the oldest California red-woods and twice the age of the bristle-cone pines previously considered the world's oldest living things.

Arizona's most ancient carbon-dated creosote fossil is a 10,850-year-old seed uncovered near Yuma in the concreted waste of a pack rat midden.

The man who once dismissed creosote bushes as dull becomes emotional when he discusses them now. Surrounded by King Clone, Vasek feels "reverent."

If he is correct, that such cloning results from environmental demands, he probably also is right in his view that the creosote bushes present in the Mohave predate those still living in the Sonoran and Chihuahuan deserts. The Mohave Desert is the harshest of the three.

Paradoxically, Vasek and most other plant specialists are convinced Larrea, from its genesis below the equator, evolved first in the Chihuahuan. They agree the species edged then - over thousands of years into the Sonoran Desert and finally across the Colorado River into California's Mohave.

Arizona's most ancient carbon-dated creosote fossil is a 10,850-year-old seed uncovered near Yuma in the concreted waste of a pack rat midden.

The creosote bushes of the Northern Hemisphere and their remaining relatives in the Monte Desert of western Argentina are so similar laymen cannot tell them apart. For years scholars labeled them a single species. Now they say those of the three northern regions differ from one another and from the Argentine plantchiefly in the number of chromosomes they contain and in minor differences in the leaves. In the Monte, almost a carbon copy of the Sonoran, the natives burn creosote bushes as fuel and thatch their adobe houses with them.

How did the scraggly shrubs make their way north from South America? No convincing explanation has been offered. Birds? Some scientists think so. Golden and upland plovers migrate annually between South and North America. So do peregrine falcons and Swainson's hawks. But seeds generally travel the avian digestive system for only a few hours. However they were transported, Larrea landed in the Southwest at roughly the same period as the earliest Indians-who were to find an amazing array of uses for the plant. Along the Mexican border, the Papagos, a few of whom continue to use it as a medicine, credit the creosote bush with a special magic. Soon after time began, they believe, it spared their major deity, l'itoi, or Elder Brother, from drowning. Forewarned of "the great flood," l'itoi, built a boat of the black shellac-a lac or gummy substance-secreted on the bush's slender stems by a scaled beetle. While the world was engulfed by the rising waters, it is told, he circumnavigated it four times before reaching the safety of the peaks of the Pinacate craters in Sonora, Mexico.

That same lac gum provided the first Arizonans with waterproofing for baskets and a glue for mending pots and affixing arrowheads. The aboriginal applications were mainly medicinal, however. Creosote bushes offered a whole drug store for a variety of afflictions, from coughs and chills to bruises, bladder stones, and rattlesnake bites. Dried, the leaves were rubbed on rheumatic limbs. The Pima Indians chewed the gummy substance to ward off intestinal ills. Even now, there are non-Indian professional people in Phoenix who swear by a "chaparral tea" brewed from the leaves. They are convinced the drink abates the symptoms of arthritis, among other things. (Actually, chaparral is the shrubby mixture of small trees, mainly manzanita and oak, that populates the Southwest's lower mountains. Sometimes, Arizonans also mistakenly refer to creosote bush as greasewood, an unrelated plant.) Mora, the Alabama microbiologist, remembers Indians in his native New Mexico who specifically relied on the same sort of decoction for that very disease. He and his co-workers at Auburn have pinpointed the “active” anti-disease component of Larrea as a phenol derivative known as NDGA, short for nordihydroguiaretic acid. They found this potent antioxidant, which concentrates on creosote bush leaves, disarms the virulent bacteria that triggers tularemia in rabbits and certain viruses in birds. When they injected the compound into human skincancer cells cultured in test tubes, the cancer cells died. The same reaction took place with mouse malignancies similar to tumors in the bone-marrow of humans. They are now trying the acid on afflicted animals. Human experiments may be in the distant future.

Also, the bushes wage chemical warfare. A defensive substance—a sort of resin they manufacture—derails the digestive tracts of most plant-eating predators. They literally could starve out the majority of the enemies eating them.

NDGA was no stranger to chemists. During World War II it helped preserve fatty foods. In industry it has been used to stabilize lubricants and rubber and prevent metals from rusting.

Creosote bushes once were the chief source for commercial NDGA, though no more. Researchers have learned to make it artificially.

One thing that intrigued Mora as a boy, he told me, was he noticed the creosote bush “is a plant that likes to be by itself. There are not many other plants growing around it, and I never saw many animals eating it.” His observation was partly valid. In fact, the shrubs are expansively spaced, almost garden-like, as if by some grand farmer. One reason each can last is few others compete with it for water. Also, the bushes wage chemical warfare. A defensive substance—a sort of resin they manufacture—derails the digestive tracts of most plant-eating predators. They literally could starve out the majority of the enemies eating them.

As is Nature's way, exceptions turn up, of course. Studies at Silver Bell, near Tucson, identified thirty kinds of insects living on Larrea; eighteen of them eat no other green plants. Among them: long-horned grasshoppers, walking sticks, scarabs, and stink bugs.

A tumblebug ingests only the green leaves, and a darkling beetle only the young stems. Without these stands of shrubs, they would not make ends meet. Although most are summer species, butterflies, moths, and treehoppers enliven the foliage in winter. One thesis holds that these arthropods coevolved with the plants in such a way their digestive mechanisms became uniquely tailored to creosote bush chemistry.

There are other adaptations, however. Some bugs eat only between sunset and midnight, when the plant's chemical defenses somehow diminish. Still other insects utilize the bushes for hiding. Crisscrossing the stalks, spiders thread their traps for prey.

The insects attract birds and lizards, next up the food chain. A handful of reptiles, such as leopard lizards and banded geckos, are restricted to Larrea flats, and the plant is the sole food for desert iguanas. Roadrunners and snakes stalk the lizards. And the chain continues. Wild bees pollinate the plants. Seed-eating kangaroo rats, which can live a lifetime without drinking, depend upon them for moisture and nutrition. Spadefoot toads, their lifespans limited to the rainstorms of summer, burrow beneath them. Because of this web of life, this network of necessity, a creosote clump comprises a microcosm of the larger desert world. None of this interdependence is more remarkable than that between creosote bushes and the litterbug termites that—to the surprise of scientists—irrigate them.

Trillions of these termites teem just below the parched soil, feasting on decaying debris cast off by vegetation. But bushes need some of that same trash for nutrients. Therefore, ecologist Walter Whitford and his students theorized a few years ago that if they could eliminate the termites, more litter would be left to fertilize the plants.

For an experiment, they selected a site on the New Mexico State University ranch -a sloping plain, or bajada, formed by water-washed soil-a perfect place for Larrea growth.

By spraying on the surface a powerful poison called clordane, they destroyed the termites all right. Yet the insect-free creosote bushes fared no better than the shrubs where termites remained.

Except for the jackrabbit and a few other desert dwellers, most animals and birds ignore the lowly creosote bush as a food source. However, a variety of insects, including the leafhopper (BOTTOM, RIGHT) and various beetles, feed only on the shrub, which may grow to a height of ten feet. In the Indian natural drugstore, Larrea has for countless ages provided poultices for wounds, teas for internal complaints, and more. James Tallon photos That led to the next question: do the termites serve some useful purpose? They do. As they forage for food below the bushes, the termites excavate honeycombs of matchstick-sized tunnels. These tiny tubes funnel the rare rainfall down to the plant roots. Dr. Whitford's team found this permits a creosote bush to blot up ten times more moisture than it would without the termites.

So now scientists no longer tamper with the pervasive, almost invisible termites that help the formerly ignored creosote bush to thrive in the North American deserts, as it has for more than an incredible 11,000 years.

Carle Hodge, science writer for The Arizona Republic, is a longtime Highways contributor whose credits also include Time magazine and Newsweek.

Wendy Hodgson is staff artist and Herbarium curator at the Desert Botanical Garden in Phoenix.

Selected Reading

Trees and Shrubs of the Southwestern Deserts (Third Edition), by Lyman Benson and Robert A. Darrow, University of Arizona Press, Tucson, 1981.

Arizona Flora (Second Edition), by Thomas H. Kearney and Robert H. Peebles, University of California Press, Berkeley and Los Angeles, 1969.

Vegetation and Flora of the Sonoran Desert, Volumes One and Two, by Forrest Shreve and Ira L. Wiggins, Stanford University Press, Stanford, 1964.