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COLUMN ONE : Detective Work That Leaves No Footprints : Getty researchers are preserving an ancient African trail by reburying it. They are battling erosion, vandals--and controversy.

TIMES SCIENCE WRITER

Faced with a ravaged work of art--a waterlogged fresco or a crumbling icon--a restoration expert gingerly removes the layers of grime, repairs the damage and erases alterations made by less deft hands, all to expose the artist’s original creation.

When the artist is nature, however, and the damaged treasure is an accidental monument to humanity’s fledgling footsteps, conservators face unusually daunting challenges. For researchers at the Getty Conservation Institute in Marina del Rey, the task at hand has been the painstaking preservation of a unique trail of footprints on an arid plain in Tanzania left 3.6 million years ago by humanity’s earliest known ancestors.

Some of the researchers’ difficulties are scientific, some political. Some go to the heart of the meaning of what they are laboring to save. And unlike a more routine restoration, in which the work of art will go on public display, these conservation experts must bury what they have so patiently refurbished.

Since 1993, Getty researchers have been working at the request of the Tanzanian department of antiquities to unearth and repair the primitive footprints, which are being undercut by erosion, disrupted by tree roots and threatened by vandalism. The group expects to finish next summer.

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As they dig, survey and photograph, the researchers are charting new territory in the realm of cultural conservation. The trail consists of the oldest known marks that humankind and its predecessors have left, offering an irreplaceable insight into humanity’s origins.

Captured in a thin crust of petrified volcanic ash, the footprints are considered too fragile to move--by some--and yet too important to neglect. And compared to a fossilized bone, they have no real substance of their own. Each imprint is only a memory held in the earth of a creature that walked the plains long before the first modern humans were born.

In their work, Getty researchers have adroitly sidestepped the region’s puff adders and prickly whistle thorns, but snagged themselves on criticism from other scientists on the sidelines who are at loggerheads over how the trail should best be preserved.

Some experts argue that the trail, which runs along the southern edge of the Serengeti Plain at Laetoli, should be moved to a museum. Others are disappointed because the site will not be opened as a tourist attraction. A few are upset that the prints are being disturbed at all. One group of researchers said the entire project is tainted by cultural imperialism.

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Other experts dismiss the criticism as “political nonsense” generated for “selfish personal reasons.”

“It does point to the fact there are very disparate perspectives on this,” institute associate director Neville Agnew said wryly.

The scientific caviling is one small measure of the contemporary passions stirred by these shallow depressions in Africa’s ancient soil.

What is at issue is the oldest known direct evidence that pre-human species walked upright on two feet, with the same free gait as modern human beings.

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The footsteps were left by three primitive individuals. The best-preserved show the impression of a surprisingly modern foot, with a raised arch, rounded heel and forward-pointing big toe.

Experts say the trail also demonstrates conclusively that erect posture came before intelligence in the evolution of humankind--freeing the hands to evolve manipulative skills and, eventually, the intellect to develop tools.

“Laetoli solved the scientific problem of which came first: the mind, the foot or the hand?” said Agnew. “Bipedalism freed the hands for toolmaking. Freeing the hands stimulated the evolution of the brain.

“Without that, there would be no humankind today,” he said.

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And for those eyes willing to see, the tracks contain a portent of the humanity that would one day follow.

Anthropologist Mary Leakey, who led the team that discovered the prints, said she feels “a poignant time wrench” when she considers the way one individual seemed to stop and turn to the left--as if glancing over one shoulder at some threat or unexpected sound--before continuing north.

“This motion, so intensely human, transcends time,” she wrote. “Three million six hundred thousand years ago, a remote ancestor--just as you or I--experienced a moment of doubt.”

Almost immediately after she discovered them in 1978, Leakey buried the imprints to shield them from the elements because there was no money for guards or a building to protect them. Scholars have steered clear of the site, worried that intensive study could damage it irreparably.

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Nonetheless, the trail was being washed away inexorably by seasonal rains. Trees were rooting in the soil over the prints. Vandals were meddling with the site.

Ironically, the excavation that brought the prints to the world’s attention also hastened the forces of destruction by loosening the hardscrabble soil and thus allowing the plants to grow more easily, researchers said.

By 1986, authorities such as Tim D. White of UC Berkeley, a prominent expert on human origins who was part of the Leakey team, were pleading with Tanzanian officials to rescue the footprints.

“Whatever is done must be done correctly the first time,” he warned. “With such fragile antiquities there is no room for error or for experimentation.”

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When a Tanzanian government official broached the idea of exhuming the footprints, Getty conservation experts had their doubts. Their reservations, however, were less a matter of expertise than of outlook.

Institute experts were more accustomed to working with the conventional artifacts of human culture, such as cave paintings in Baja California, tombs in Egypt’s Valley of the Queens or a David Siqueiros mural in Downtown Los Angeles. Most recently, they designed the hermetically sealed cases that preserve the handmade parchment documents of the constitution of India in an inert, nitrogen-rich atmosphere.

In contrast, the Laetoli footprints are fossils--works of nature, not of an artist’s hand.

The institute’s sole purpose is the conservation of cultural artifacts, not scientific specimens. It took some argument before the Getty specialists could convince themselves that they should get involved.

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“If we are here to promote the conservation of cultural sites around the world, you could look at this as the beginning of all cultural sites,” said Martha Demas, who is supervising the Getty’s work at Laetoli. “Bipedalism led directly or indirectly to the beginning of all culture.”

When Demas and her colleagues began fieldwork at Laetoli last summer, there was little on the surface to indicate it was such special ground.

A berm of dark lava boulders marked the general outlines of the site. Thirty-seven acacia trees sprouted from the shelter of the rocks. Spikes of grass anchored the soil, but decades of rainy seasons had left their imprint in the dry outwash. A gully yawned at one end.

After preliminary surveys, the restoration crew began by reopening the first 30 feet of the trail. For three weeks the team dug.

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“We weren’t exactly sure where the footprints were under the older covering,” Demas said. “There were no real markers or data points from the [original] excavation. There was no published plan of the trenches. . . . We were in some way digging in the dark.”

The footprints are the unlikely product of unusual mineral chemistry, the start of a rainy season and a volcanic eruption.

The volcanic rock that contains them is about six inches thick, comprising a series of layers of volcanic ash that fell millions of years ago, explained Getty scientist Eric Doehne. The volcano believed to be the source of the eruption still looms on the horizon about 20 miles to the east. Each layer represents perhaps no more than a few hours of ash fall.

As each layer accumulated like a dusting of new snow, it apparently recorded all that touched the earth, from raindrops and falling leaves to the tracks of hundreds of animals.

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The pre-human footprints were made at a moment when conditions were just damp enough to hold the ash in place but before heavier seasonal rains started, experts believe. A hard rain would have washed them all away. A drier ash would have blown away like the finest face powder.

The chemical content of the ash--high in carbonatite--meant that it was cohesive when damp, forming an excellent mold for capturing prints, Doehne said. Over time, the carbonatite was replaced by calcite, which formed a durable but delicate cast.

“It is very friable material,” said Leakey in a telephone interview from her home in Nairobi, Kenya. “It is not like a hard rock. It is a crumbly volcanic ash full of cracks.”

To get at the prints, the Getty scientists moved the boulders and shoveled away the layers of soil and rock around each sapling sprouting from the trackway until they could be certain how much damage the roots had caused. The soil was unexpectedly sodden.

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They quickly uncovered a distinctive layer of compacted gravel that Leakey had used to cover the impressions. They abandoned their larger tools and, working with white gloves, brushes and wooden picks, began clearing the last layer of sandy clay centimeter by centimeter.

Finally, the dark hollows of the footprints re-emerged.

“What was extremely fortunate was that there was very little root damage to footprints,” Demas said. In most spots, the trees either grew around the tracks or their roots were deflected by the hardness of the calcite tuff.

Nonetheless, when the researchers surveyed the exposed trail, they saw that at least two prints had been disrupted by roots, she said.

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As they continued to clear away the trail, they noticed a dark halo around each imprint that had been left by a chemical used to harden the site in 1979. Examining the stains under a microscope, the team saw that the layer was separating away from the rest of the tuff and starting to crack. Although the chemical may further damage the prints, it was too risky to remove, they decided.

Unable to study the prints firsthand, scientists over the years have had to make do with photographs and a cast made by the Leakey team. The Getty researchers were eager to correct any inaccuracies in the records.

Flaws in the original casts made it hard to tell details of the impressions from quarrying marks left by the 1979 excavation. More than one bitter academic quarrel erupted over whether one set of marks represented an ancient heel print or the slip of a modern chisel.

“The casts represent an incomplete and sometimes misleading guide to the trails,” White said.

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The conservators painstakingly photographed, analyzed and measured the site, then created a digital map to accompany the images. They also made casts that were more accurate.

Then they buried what they had exposed. Although this was an essential part of the restoration, “it was troubling and sad when we began to put the first layer of sand over the footprints--and we all felt this,” Demas said.

It was no conventional burial. From a riverbed several miles away, they trucked in suitable sand, sieved it to get the proper, rounded grains, then spread it two inches thick over the footprints.

Then they spread out a layer of a special cloth designed to absorb water without allowing any erosion. Over that they spread a distinctive layer of gray soil to serve as a marker for any future excavators, then another layer of sand. They added a sheet of yellow fabric woven with nodules of herbicide, designed to leach out over the next 80 years. More soil was spread, followed by another sheet of material to block roots.

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A nylon sheet to retard erosion came next, then even more soil. Finally, they rolled a new mound of lava boulders into place.

To help ensure that no casual curiosity seekers would vandalize the site, the Getty team persuaded the local Masai villagers to make the trail of their most distant ancestors a sacred site.

Next summer, the Getty group will dig up and restore the second half of the trail, which appears to have been more seriously undercut by erosion. Then they will rebury it.

Leakey called the effort--which is funded by the Getty trust--"splendid,” “very careful” and “well thought out.” Still, she would rather see the prints housed in an open-air museum. With no government money for such a plan, however, she says the trail is safest under its blanket of earth.

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“They are burying them with preservative measures until such time as Tanzania might have the infrastructure to put up a museum on the spot,” she said. “Things would have to alter radically before that would be feasible.”

Although White at Berkeley says he approves of the Getty’s work, he insists that the only way to save the trail is to move it to a museum.

“Preservation in place is doomed to fail. The only way to preserve the prints is to remove them,” he said.

“Nobody knows what will happen next. Maybe they will be OK for another 200 years. Maybe the Masai will dig them up and poke at them with spears in 10 years,” he said. “In the long run, however, in this remote and unprotected locale, the prints will disappear altogether. This is inevitable.”

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Tanzania wants the footprints to stay where they are. And Getty officials bristle at the suggestion that the trail should be removed from the land in which it was formed so long ago.

“Here the footprints are part of the landscape, and the landscape today is evocative of the conditions in which humankind evolved in East Africa,” Agnew said.

“It is a subtle point perhaps,” he added, “but the footprints are part of that landscape, within sight of those volcanoes in a biosphere that is very similar today [to what] it was 3.5 million years ago.

“To take it out of context would be to gut the site.”

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Preserving Prints

A team of Getty researchers has been working in East Africa to unearth and repair footprints made by pre-human species, which had been endangered by erosion, tree roots and vandalism. They hope to preserve the oldest known marks that humankind and its predecessors have left on the planet.


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