Recent news that a team of international researchers discovered a 3.8-million-year-old fossil in Ethiopia generated worldwide interest because the “remarkably complete” cranium is a rare find of an early human ancestor.
To help determine the fossil’s age, a Franklin & Marshall College geoscientist examined igneous rocks from that region in his campus laboratory. Stanley Mertzman, the Earl D. Stage and Mary E. Stage Professor of Geosciences, works with researchers in that region of Africa.
“I’ve been working with them off and on for 30 years,” Mertzman said. “They send me igneous rocks to chemically analyze using X-ray analysis, from lava flows to air-fall pyroclastic material; I send back reams of data and my thoughts concerning which samples go together.”
Mertzman’s rock analysis was helpful to the paleoanthropologists who were attempting to determine the absolute age of the fossil and its relation to the evolutionary history of humans. He was unaware, as is custom in such research, of the purpose for analyzing the suite of rocks from where the cranium, referred to as MRD-VP-1/1, was discovered.
“I had no idea,” Mertzman said. “Paleoanthropologists always want to bracket significant fossils between layers of igneous material as closely as possible. Absolute age dates can be determined from igneous rocks using one or more radioactive decay systems. Doing so helps pin down more precisely when the hominid walked the Earth.”
Cleveland Museum of Natural History Curator and Case Western Reserve University Adjunct Professor Dr. Yohannes Haile-Selassie and his team discovered the cranium, a human ancestor from the Woranso-Mille paleontological site, located in the Afar region of Ethiopia.
The researchers said MRD generates new information on the overall craniofacial morphology of Australopithecus anamensis, a species widely accepted as an ancestor of Lucy’s species, Australopithecus afarensis, discovered in Ethiopia in 1974. MRD also shows that Lucy’s species and its hypothesized ancestor, A. anamensis, coexisted for approximately 100,000 years.
This data challenges previous assumptions that there was a linear transition between these two early human ancestors, Haile-Selassie said. “This is a game changer in our understanding of human evolution during the Pliocene,” he noted.
The team worked 15 years at the site before its February 2016 discovery that represents a time interval between 4.1 and 3.6 million years ago when early human ancestor fossils are extremely rare, especially outside the Woranso-Mille area, according to the paleontological researchers.
In the years that follow their discovery, the paleoanthropologists on the project conducted extensive analyses of MRD, while project geologists worked on determining the age and context of the specimen. The results of the team’s findings are published online in two papers in the international scientific journal Nature.
In a companion paper published in the same issue of Nature, Beverly Saylor of Case Western Reserve University and her colleagues, which included F&M’s Mertzman, determined the age of the fossil as 3.8 million years by dating minerals in layers of volcanic rocks nearby. They mapped dated levels to the fossil site using field observations and the chemistry and magnetic properties of rock layers. Saylor and her colleagues combined the field observations with analysis of microscopic biological remains to reconstruct the landscape, vegetation and hydrology where MRD died.
Additional information for this story was provided by the Cleveland Museum of Natural History.