Theme Scientific Breakthrough

Investigated deposited sediments

Gerard De Geer was a famous professor of geology at Stockholm University. At the end of the 19th century, De Geer began investigations of deposited clay sediments and made accurate measurements of their thickness. He had a theory that it was possible to date the end of the latest ice age by counting layers of clay deposited in lakes and fjords when the inland ice melted. Like annual rings in a tree, these layers of clay had built up, a lighter, thicker layer in the summer and a darker, thinner one in the winter.

Studied varves of clay in the emptied Lake Ragundasjön

Early in the 1900s, De Geer and his students came to Ragunda. He had realized that Ragunda was a perfect location for studying varves – layers – of clay. After Lake Ragundasjön had been emptied of water the varves were easy to study.

The uppermost layer dated from 1796, the year when the lake was emptied. From there it was just a matter of counting backwards in time, and connecting the clay layers to a time scale. The bottom layer was approximately 7,000 years old. Since the varves are unique, De Geer and his students were able to make comparisons with other, corresponding layers in other places, where they could count more layers further back in time. This way they could create a very long time scale.

The Swedish Time Scale

De Geer’s intention had been to calculate the end of the latest ice age, but the application of his measuring method found far wider use than this. He also believed that it was possible to correlate sediment all over the world, but these ideas proved not correct.

The varve chronology system that De Geer invented was called The Swedish Time Scale. It was the geological science´s first absolute and more exact means of measuring time.  

The Geochronological Museum is housed in the Department of Geosciences at Stockholm University. Here you can find much of the material connected to Gerard De Geer and the varve chronology research.