At MARUM, the Center for Marine Environmental Sciences at the University of Bremen, there is a place that holds more than 200 kilometers of material drilled from the ocean floor. More than 350,000 core pieces. Collected over 55 years of scientific expeditions across the Atlantic, the Arctic, the Mediterranean, and the Black Sea. One of only three places like it in the world.

This is the Bremen Core Repository. And it is, in the words of the scientist who has guarded it for more than three decades, an Earth history book.

In this episode, we meet Doctor Ursula Röhl — Ula — the head of the Bremen Core Repository Group, who has witnessed the development of this archive from its foundation in 1994. She is joined by Doctor Thomas Westerhold, whose 66-million-year climate record was built entirely from these cores; Doctor Matthias Zabel, who reads the carbon signals buried in the sediment to understand how the ocean responds to our emissions; Doctor Enno Schefuß, who tracks individual molecular fingerprints inside the cores to reconstruct the climate history of entire continents; and Doctor Verena Hoyer, who has sailed on multiple drilling expeditions and discovered life in places where no one expected to find it.

Through their voices, we discover what is hidden inside kilometers of gray mud: the rhythm of the planet, the record of past climate changes, and the evidence that will help us understand where we are going.

This podcast was produced as part of the FRONTIERS Science Journalism Fellowship, funded by the European Research Council under the European Union's Horizon Europe research and innovation programme. The residency was carried out at MARUM, the Center for Marine Environmental Sciences at the University of Bremen, Germany. Graphic design was supported by Leonardo.ai.