One of the things that deeply bothered me for a lot of my childhood was “how do ancient cities get buried?” It kind of makes sense in the desert, where sandstorms can turn a house into a dune, but the random discovery of relics deep within Earth was mysterious. How do they get down there? Well, as a homeowner, I’ve come to appreciate that there is a constant build-up of pollen, dust, leaves, and other debris that would very much like to bury my yard and that tries to do so year after year. 

I have made it a personal mission to defeat the detritus, but your average forest floor doesn’t have someone protecting abandoned cottages from slowly getting lost to time, leaves, and soil. Given the fullness of time, the year-on-year build-up of materials goes on to form the layered strata revealed on cliff faces and highway cutouts. These are the layered stones searched for fossils and the trace elements of cataclysmic periods of volcanism or asteroid impacts. 

The deepest layers of Earth’s past get lifted into view through plate tectonics. When two parts of the Earth’s crust collide, the plates lift up to form mountains, and we see those past layers. In different places, different pieces of the past are revealed, but sometimes, parts are missing. Flooding, landslides, and other major events can wipe away chunks of history, leaving an incomplete record, and for one epoch of the past – from about 94 million years ago to 86 million years ago – no complete record had previously been found. This epoch corresponds to the late Cretaceous period and the end of the reign of dinosaurs. The world is large, however, and the mountains are many, and scientists recently recognized that the cut-away layers revealed in a German limestone quarry are the missing perfect record. 

Located in Hasselberg, this quarry has a 40-meter section of exposed rock that – without any layers missing – captures the Earth’s history. According to lead researcher Ireneusz Walaszczyk: The sequence … prevails over other candidates, for example from the USA, India, Madagascar, New Zealand and Poland, because we have a perfect rock boundary sequence here over 40 meters, with a well-defined record of events which took place in this interval of geological time.

Co-lead Silke Voigt goes on to say: This is important in order to be able to make an exact chronological classification even in the case of incomplete successions and ultimately to see, for example, what the climate was like at a certain time in the past in different places in the world. 

This work appears in the Episodes Journal of International Geoscience.

More Information

Goethe University press release

“Reassessment of the Salzgitter-Salder section as a potential stratotype for the Turonian–Coniacian boundary: stable carbon isotopes and cyclostratigraphy constrained by calcareous nannofossils and palynology,” S Voigt et al., 2021 April 9, Newsletters on Stratigraphy

“The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hauterivian Stage (Lower Cretaceous), La Charce, southeast France,” Jörg Mutterlos et al., 2021 June 1, Episodes