Radioisotopic ages of newly discovered fossil sites hold clues to evolution of mammals

Anatolia, the western part of modern-day Turkey that sits at the crossroads of Asia, Africa, and Europe, is a fossil-rich land crucial to unlocking the mysteries surrounding the evolution of mammals over the last 10 million years. Despite the abundance of fossils from the Middle and Late Miocene (about 16 to 5.3 million years ago), scientists have to rely on indirect methods—like studying changes in the Earth’s magnetic field and comparing fossils from distant and uncertain locations—to estimate the age of the remains, due to lack of volcanic materials.

A recent discovery of fossil-rich Late Miocene sites in the Central Anatolian Volcanic Province by an international research team could be a game-changer in tackling these scientific challenges and could shed new light on the evolution of mammals, including early humans and their ancestors.

The findings are published in the Proceedings of the National Academy of Sciences.

Volcanic deposits are rich in radioactive isotopes, which provide chemical signatures essential for determining the age of fossils. A process called radioisotopic dating leverages the presence of such radioactive material to measure the date of geological materials like rocks by measuring the decay of a radioactive “parent” element into a stable “daughter” element, a process known to occur at a constant rate.

For this study, scientists irradiated feldspar rock samples collected from six different sites across the volcanic province with neutrons. The flux of neutrons converted the Potassium-39 in feldspar into Argon-39, which then acted as a proxy for potassium in the dating process.

The sample was heated to release trapped gases, including Argon-39, which was created during irradiation, and Argon-40, the daughter product formed by the natural radioactive decay of Potassium-40 over time. By measuring the Argon-40/Argon-39 ratio, scientists calculated how much Potassium-40 was originally in the rock, allowing them to determine its age accurately.

Powerful volcanic eruptions often deposit layers of ash and rock around fossils, forming distinct volcanic layers above and below them. Since these volcanic layers of the recently uncovered sites can be accurately dated, researchers established a precise timeline for the embedded fossils, thus offering fresh insights into the evolutionary journey of mammals in Anatolia and surrounding regions without volcanic deposits.

The researchers believe that high-resolution satellite images can guide the exploration of many such undiscovered fossil sites across the region, each with the potential to reveal pieces of the evolutionary puzzle from different periods of Earth’s history.

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