Humans linked to earliest fossils

Bones dug up in eastern Africa date back to some of the oldest remnants of human beings and other species, and although we know their ages, scientists have had a hard time making it relative to today.

On the 150th anniversary of the first publication of Charles Darwin's "On the Origin of Species," University of Utah Dean of the College of Mines and Earth Sciences Frank Brown said Tuesday that there have been several branches of the human race but only one as resilient as the current human race.

"Our family tree runs back to the very beginnings of life," he said during the U.'s Frontiers of Science lecture. Human evolution is tied to prokaryote organisms, the first documented creatures on earth, through the finding and dating of fossils throughout the world.

In 1959, Mary Leakey discovered a fossilized human skull in Tanzania that was dated to 1.75 million years old by the potassium-argon dating method. The unusually well-preserved skull was an astounding find and changed thinking about the antiquity of early man.

"Fossils tell us a great deal about ancient environments," said Brown, who is also a distinguished professor of geology and geophysics at the U.

Through the decades, scientists have improved ways of determining the correct ages of bones and fossils, through the correlation of many fields, including the study of volcanoes and the spread of volcanic ash. Those discoveries are based on fieldwork in the Omo-Turkana Basin in southern Ethiopia, where Brown has made many visits.

"Through work in Turkana and elsewhere, most fossils can now be placed in time relatively well," he said.

Work of scientists has yielded nearly 1,000 fossils of early humans ranging in age from about 4.2 million years old to less than 10,000 years old. Nearly all of these are well dated, to a precision of 1 percent, because the volcanic ash layers provide excellent materials for dating based on the decay of radioactive potassium and because the record of the ancient magnetic field of the Earth has been established in the sections that are studied.

Brown said that there is much work to be done to relate the findings to current populations but that knowing the ages is important.

"We have a good idea of the environments in which our early relatives lived but are unsure of how they made a living," he said. Such details are left to study, but one thing is for sure, he said, "there were several branches of our human family and for some reason, we're the only one that has survived."

e-mail: wleonard@desnews.com