Where “chalk” meets “jurassic”

If you want to build a house, and especially if it is to have a cellar, it is good to know what kind of stone the subsoil is made of. The fact that these rock layers beneath our pits are so well researched today is due to stratigraphy. Geology is a branch of geology that has set itself the goal of arranging the individual rock layers of the earth from old to young.

The layers are not distributed randomly in the earth’s crust; each one was created at a specific time in a specific place. So if you want to find a very special raw material underground, stratigraphy will tell you where you can successfully search for it. Stratigraphy also proves helpful in the construction of roads or railroad lines, because it shows where there are layers of rock that are better avoided from a structural engineering point of view.

The stratigraphers are organized since 1970 in the german stratigraphic commission (DSK). Today, it has 420 members from a wide variety of fields, mainly geologists, mineralogists and geographers, but also "amateurs" are thereby, as hans-georg herbig, DSK chairman and professor at the universitat koln, reports.

The DSK is currently holding its board meeting at the coburg museum of natural history. Eckhard monnig, an employee of the museum and himself a member of the DSK, invited the audience to attend. Monnig had dedicated an exhibition in 2018 to the coburg polymath and former director of the gymnasium casimirianum, johann christoph matthias reinecke. Reinecke, as a natural scientist, had scientifically described 40 different jurassic ammonites and thus laid the foundation for stratigraphy. The determination of rock strata on the basis of fossilized flora and fauna is today the heart of stratigraphy.

Terms like "jura or "chalk time everyone has probably heard of this, even if they don’t know anything about stratigraphy, says markus wilmsen, second chairman of the DSK and palaontologist at the senckenberg museum in dresden. The naming of the rock layers was at the beginning of the 19. Century defined. It is internationally valid. In many cases, there are names that indicate where a particular rock is particularly abundant, for example eifelium (eifel), emsium (emsland) or aalenium (aalen).

Where was sea, where was mountains?

Eckhard monnig calls the classification of the earth’s history on the basis of rock layers and fossils "one of the greatest achievements" of research. It is possible, for example, to determine whether there was a sea or perhaps a mountain in a certain place at a certain time. The sequence of the layers can be compared to the stack of paper on the desk, explains markus wilmsen with a wink: "what is at the bottom is definitely old, what is at the top is newer"."

Thanks to stratigraphy, it is now clear that the earth is about 4.6 billion years old, says wilmsen. The oldest stratum is called hadaic and covers the first 600 million years of the earth’s history. The present time period, the holozan, began about 11 700 years ago. Younger strata can be determined to within 100,000 years, older ones to within plus or minus one million years. For science, this is very accurate, but for the "normal" person, it’s not people, as professor herbig admits "the dimensions we have to deal with are hardly imaginable".

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