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The youth was tall and lanky, and he died near a river in eastern Africa. Maybe he slipped on mud and the fall did him in; maybe he had been ill; just possibly, an animal killed him.

His body lay in a flood basin beside the river. Soon after his death, hippos wandered through and trampled his remains into the mud, scattering the bones.Not much else is known about the boy, except that his fossilized bones make up the earliest skeleton of the homo line, the genus of humans to which our own species, homo sapiens, belongs.

Scientists have named the specimen the "Turkana Boy." The youth lived between 1.39 million and 1.64 million years ago.

That we know approximately when he roamed the underbrush is thanks in large measure to the work of Frank Brown, dean of the College of Mines and Earth Sciences at the University of Utah.

Brown has traveled to Africa just about every year since 1965 on expeditions to calculate the dates of strata where fossils are found.

Oldest-known skeleton

One of the most important finds that Brown has worked with was that of the now-famous Turkana Boy, discovered in 1984 by Richard and Maeve Leaky and their team of scientists. This mod ern human, which has the specimen designation "WT 15,000," is the oldest and best-preserved skeleton of the Homo erectus line, believed to be ancestral to our own.

Brown was part of the archaeological team working in a remote part of Kenya called Nariokotome, west of Lake Turkana, when the fossils were found. Through the years, as more was learned about the remains, it became increasingly famous.

The priceless original bones are housed at the National Museum of Kenya, Nairobi.

Recently Brown obtained a replica of the bones from the museum. He has been preparing the replica for display in the eight-story Browning Building, which is occupied by the college.

"When classes are over, then I'll have time to figure out how to mount this thing," Brown said during an interview on campus. For now, the casts of the bones are scattered across a table, startlingly lifelike.

Turkana Boy's skeleton tells us he wasn't full-grown. The ends of the tibias haven't fused where they were attached to his ankles, showing that he was still growing. The wisdom teeth had not erupted; more than a million years later, they remain embedded in the bone of his upper jaw.

The dark skull seems small by today's standards, but the body is surprisingly large.

"Look at this - his femur - it's not quite as long as mine," Brown said, holding the bone beside his own upper leg. The cast is almost as long, and Brown is 6 feet 4 inches tall.

When alive, Turkana Boy probably stood 5 feet 9 inches tall. As an adult he would have reached about 6 feet 1 inch, anatomists calculated.

But even fully-grown, he would have weighed only 165 pounds.

Reconstructing environment

One of Brown's colleagues, Craig Feibel, helped reconstruct the ancient environment of the area. A research professor and a former graduate student of Brown's, Feibel is a co-author with him of an important paper in a new book compiling reports about the Turkana Boy.

A million and a half years ago, the site was a muddy little flood basin beside a river. Animals went to the river, trampling the youth's remains and leaving big footprints in the fine siltstone. "Some of the bones were broken," Brown said. "Some of them were actually standing almost vertically."

Far back in prehistory, volcanoes fired their ash and pumice into the air periodically throughout that region of eastern Africa. Samples of the resulting layers have been dated by Ian McDougall of the Australian National University, using known rates of changes in potassium and argon isotopes.

"We can date one of these ashes in one place, and then we recognize them in another place," Brown said.

That's his contribution: recognizing the different layers through a process called tephrachronology. "Every eruption is different" in its chemistry, he said.

Chemical dating

Each time a volcano explodes, a different mix of chemicals goes into the air. Brown can take samples of a layer and tell whether it is a chemical match with samples that have been dated elsewhere.

He has built up an encyclopedic knowledge about volcanic eruptions of this region and in other sites important to the study of early humans, including Pakistan, China and Ethiopia.

In the case of the Turkana Boy, a volcanic layer below the bones was dated to 1.64 million years ago while a layer above is 1.39 million years old. That bracket puts his age at approximately 1.5 million years.

The date may be narrowed as another layer is dated - one closer beneath the skeleton.

Soon, visitors to the second-floor foyer of the College of Mines and Earth Sciences will see the replica and remember that the College of Mines and Earth Sciences isn't only concerned with locating minerals. It covers meteorology, paleontology, oceanography and many other geological disciplines.

But more than that, they'll gaze upon an exact cast of the bones of this early person, and wonder.