An archaeological find that takes us back to our roots 3,5-million years ago is disappearing. But a Cape Town engineer has used a unique method to capture it for the future, writes Lesley Cowling
MORE than 3,5-million years ago, three of our ancestors wandered north across the Tanzanian grasslands, following traditional game trails. Like the other migrating creatures of the African plains, they were moving back to the savannah at the end of the dry season.
They noticed they were walking across a stretch of ash that hadn’t been there before. It was ash from the eruption of a volcano about 20km to the east, now known as Sadiman. The ash did not disrupt their easy progress as they walked, like we do, upright with their hands hanging free. And if they had turned to look back, they would have seen a trail of their footprints clearly marked in the fine damp ash.
They moved on. Some time later, ash began falling again and buried their tracks. The layers cemented, probably because of the rain, and the footprints were hidden and preserved a few centimetres below the ground.
Time passed. Great religions sprung up, empires rose and fell, Africa was colonised and decolonised, and the descendants of the hominids became fascinated with the past. This fascination brought them to the relatively new country of Tanzania, near a lake now called Eyasi, where the rock-beds formed by volcanic eruptions millions of years before hold clues to the origin of modern creatures.
Geologists call them the Laetoli beds. They stretch for 1 500km2 and they contain many animals, plants and other objects from millions of years ago. The beds are laid down in narrow shelves of rock, only centimetres thick. Recent weathering has split these layers, opening up the bed’s long-buried secrets.
For archaeologists, it is a rich resource, where they have been exploring and collecting for 60 years. In 1978 an American called Paul Abell discovered an unmistakable human footprint. He and others cleared away the top layer – that fall of ash that had preserved the footprints – and found two long parallel trails.
The third set of footprints was on top of one of the other sets, made by a hominid walking in the footsteps of the biggest one. It looks like he or she was following closely behind. The footprints all come together at one point, as if they had stopped and looked at something before carrying on.
Footprints in the sands of time? Well, depending on your orientation, the existence of these tracks is either a miracle, or an incredibly lucky coincidence of natural events.
But ironically, the discovery of the footprints may be as transient as most miracles – after 3,5-million years of preservation, the prints are threatened. Opening them up has exposed them to the elements, and has made them vulnerable to tree roots and other plants that grow in the area.
The central issue of the footprints is no longer how they were preserved or what they tell us about evolution. The problem is how to conserve them for future generations.
Experts have opted for burial. They recently covered the prints with synthetic materials that contain time-release herbicides, to keep out the roots. Archeologist Mary Leakey, one of the first explorers of the area and part of the group present at the original find, says: “You’ve got to bury it if you want to preserve it.”
The problem with this is the footprints are no longer available for study. Experts all over the world cannot access them to test their theories or find out more about these early ancestors of human beings.
Enter Dr Heinz Rther, engineer and head of the Department of Surveying and Geodetic Engineering at the University of Cape Town. Surveying is traditionally thought of as the practical skill of mapping out the landscape, usually be-fore putting roads or bridges across it. It has to be precise, accurate and makes use of sophisticated equipment, including specialised cameras.
But surveying is no longer only the vanguard of construction teams. Experts like Rther have been using surveying for a wide array of inventive things in a number of disciplines.
One of these areas is conservation. With their sophisticated photographic equipment, surveyers can make accurate three- dimensional digital maps of archaeological sites, which can be used on CD-ROM discs for visualisation, virtual reality or other computer applications. Usually, they photograph, or rather, photogrammetically survey buildings, machine parts, human bodies or animals. But, in principle, the techniques can be applied to any object.
So when the Tanzanian government and archaeological experts decided to bury the footprints, the Getty Conservation Institute, part of the Paul Getty Trust which has an interest in the project, decided to get Rther to go along and record them photogrammetically before they disappeared from view.
For him, it was a dream project. As you would expect, he is a precise man. His UCT office is clean and airy, and his shelves are ranked with neatly labelled files and many objects from his travels. It is a far cry from the remote wild grasslands of the Laetoli area, where the Maasai still live in the traditional way and regard strangers with suspicion.
Rther describes it as a very special experience. He was part of a group of scientists from a number of disciplines who had an encampment in the veld and were driven by four-wheel-drive to the site every day.
Ruther and his team worked from early morning until it was dark, taking pictures, recording and surveying with painstaking precision. They had to treat the footprints in the same way as hills and landscapes – and make a detailed map of each imprint, treating it as if it were a topographical surface, showing every fluctuation.
This kind of accuracy is vital for study of the footprints. The exact shape of the imprint and the depth at various points can help experts to analyse the way our ancestors walked. For example, did they swing their arms like we do, or walk with them close to the body?
“For photogrammetic recording, it is essential to have some points in the recording area which are known to the highest precision,” Rther says. “These serve to determine the positions of the cameras during photography, which in turn allows the determination of the positions of surface points.”
They started out by using precise engineering surveying techniques to determine the exact positions of control points. Then each footprint was photographed several times from different positions.
After Rther and his team had done their work, and the archeologists, geologists and anthropologists had completed theirs, the footprints were carefully covered.
Rther says one of the special moments of his time there was a traditional ceremony held to bless the site. The scientists had been asked to limit contact with the Maasai and not to photograph them, to minimise the group’s impact on the area, so this was the only time the visitors were brought together with them. He says initially the Maasai were suspicious of all the activity around the footprints, but once they understood what they meant, they treated the site with great reverence.
Back home again in Cape Town, the pictures were converted to computer files. Some 10 to 20 000 points were automatically determined for each footprint using state of the art software developed by Rther and his digital photogrammetry research group. They generated 30 000 computer files to produce the final 1 500 files that they sent to the Getty Conservation Institute last month.
Rther says the Getty Institute wants to create a CD-ROM on the footprints. He says it is now possible to create virtual reality sites, where the viewer can “fly” over the footprints or through them.
“This is not conservation in the physical form,” he says, “but something which is also of real value. It has a scientific and general knowledge value.”
And it is especially important in this project. Although everything possible has been done to conserve the footprints, they are no longer safely hidden in a volcanic rock-bed. They are now fragile, and scientists fear that they may not last. Finally, like most human tracks, they have become transient.
ENDS