Credit: Ferhat Kaya
Researchers have dated volcanic layers at six fossil-bearing sites in Turkey, including one known as Taşhan (shown). The results help pin down dates for ancient mammals found at the site, and reveal relationships among species in Africa, Asia, and Europe.
Around 11 million years ago, a cooling climate fragmented warm, humid forests in Africa, Asia, and Europe, giving rise to savannas. Many mammals evolved to take advantage of these wide-open spaces, including species similar to the giraffes, rhinos, buffalos, jackals, and hyenas that roam East African savannas today. New radioisotope dates from fossil sites in Turkey may help researchers untangle the evolutionary history of mammals, including early humans and their relatives (Proc. Natl. Acad. Sci. U. S. A. 2025, DOI: 10.1073/pnas.2424428122).
“Turkey is very crucial because Turkey is placed in between the continents,” says Ferhat Kaya, a mammal paleontologist at the University of Oulu and one of the paper’s authors. Fossils from Turkey could show links among mammal species in Africa, Asia, and Europe and provide clues about past migrations.
Due to its position between the Earth’s crustal plates, Turkey is a hot spot of tectonic activity, including volcanic activity. The volcanic layers produced by eruptions can be used for geochronological dating, Kaya says.
The team used argon-argon ( 40Ar/39Ar) dating—a technique based on the abundance of isotopes of argon—which has been around since the 1960s. “This method is unique in that when the clock starts ticking, so to speak, is relatively unambiguous,” says paper coauthor Paul Renne, a geologist at the Berkeley Geochronology Center.
Unlike lead-uranium dates, which correspond to the formation of certain crystals in magmas, argon dating dates the eruption itself. The technique takes advantage of the natural decay of potassium-40 to argon-40. In magma, this argon-40 diffuses out, so there’s essentially no argon-40 when this rock is first erupted, Renne says. Over time, potassium-40 in the rock decays to argon-40 and is trapped in the structure of the minerals, providing a way to date the samples.
Volcanic deposits—including tuff, a type of rock formed from volcanic ash—contain bits of feldspar, an aluminosilicate mineral that contains potassium and an amount of argon that depends on the time since the eruption.
Renne’s graduate student Andrew Tholt went to Turkey to sample the volcanic rocks at six locations. At some sites, he was able to sample layers of volcanic rock that sandwich layers stuffed with fossils. These dates provide fairly precise time stamps in contrast to other commonly used dating methods, Kaya says. These new dates could help refine dates obtained via other methods at nearby areas, he says.
“If you find a radiometric analysis . . . it’s always good news,” says Lars van den Hoek Ostende, a mammal paleontologist at Leiden University who wasn’t involved with the work. But it’s not yet clear what the dates have to say about the evolution of mammals, apes, and humans as the researchers haven’t fully described the fossils found at these sites, he says.
Kaya’s team suspects the new dates may help paleontologists answer questions about where the apes that eventually evolved to become humans originated, whether it was in Europe or Africa. Some of the key fossils in that debate are from Turkey or surrounding areas, including Greece.
Identifying and studying the fossils found between the newly dated layers will be critical, van den Hoek Ostende says. “Now the real work starts.”
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