Unravelling the history of the rocks: the Bromacker is 4 million years older than previously thought

(Kopie 16)

When a few millimetres make a difference of four million years: as part of the BROMACKER project, a team of scientists – including Dr Lorenzo Marchetti from the Museum für Naturkunde Berlin – has discovered that the famous fossil site between Tambach-Dietharz and Georgenthal in the Thuringian Forest is older than previously thought. 

Analysis of a volcanic ash tuff layer just a few millimetres thick, discovered during the 2024 excavation, revealed that the fossil-bearing rocks of the Bromacker are 294 million years old – making them four million years older than previously thought. The findings have now been published in the journal ‘Gondwana Research’. 

“When we uncovered the dark, reddish-purple ash layer, the difference from the surrounding rock was immediately apparent, and we were very hopeful that we had finally found material that could be dated,” says Sophie König, who works as a museologist for the Friedenstein Foundation on the BROMACKER project and is a co-author of the newly published article. “The fact that the rock sample actually contained usable zircons still came as a surprise to me. We are delighted to have added an important scientific building block to the highly successful Bromacker project.” 

To date the age of an ash layer, scientists use the internal clocks of rocks, which are embedded in certain minerals. In this case, the mineral zircon was considered; although it is very small, it has the best long-term memory. At Friedrich Schiller University Jena, zircon crystals were extracted from the rock sample collected at Bromacker and analysed radiometrically at the TU Bergakademie Freiberg. 

As the only facility in Germany, researchers here trace the history of the rocks in a metal-free cleanroom laboratory using U-Pb CA-ID-TIMS – a uranium-lead dating method – and can thus date their age with high precision. 

The results of this new dating have implications for research into ecosystems and fossils from other fossil deposits of similar age that, like Bromacker, formed on the supercontinent Pangaea. The age of these fossils can now be determined more accurately thanks to correlation with the Bromacker fossils, which have now been precisely dated. 

“This exceptional fossil site, which provides so much information about Permian ecosystems, required precise dating to become a global reference for biostratigraphic, palaeoclimatic and evolutionary studies. Careful exploration of the Bromacker site led to this unexpected but urgently needed discovery of an ash layer containing well-preserved zircon crystals,” says Dr Lorenzo Marchetti, lead author and researcher at the Museum für Naturkunde Berlin.

The new age has implications for our scientific understanding of early ecosystems and terrestrial vertebrates: the food web as we know it today developed earlier than previously thought. The time span between the first appearance of herbivores and the development of modern food webs was shorter, demonstrating that the evolution of the Bromacker organisms proceeded more rapidly than previously thought. Thanks to the new dating, it is now clear that all these evolutionary innovations and the transition to a more seasonal climate occurred significantly earlier than the scientific community had previously assumed. 

“The re-dating of the fossil site is part of the BROMACKER collaboration, funded by the German federal government and the Free State of Thuringia, and a prime example of what is scientifically possible when experts from a wide variety of institutions join forces for a joint project. Bromacker has developed into an innovative and interdisciplinary research and science communication programme built on decades of international collaboration, and above all has enormous potential for the future,” says Dr Tom Hübner, head of the BROMACKER project at the Friedenstein Foundation in Gotha. 

Publication: Marchetti, L., Stubenrauch, J., Käßner, A., Tichomirowa, M., König, S., Pint, A. & Voigt, T. (2026). First high-precision radioisotopic age from the Permian Bromacker Lagerstätte (Tambach Formation, Germany) and implications for biochronology and biota evolution. Gondwana Research, https://doi.org/10.1016/j.gr.2026.02.005.