December 17th 2019

Norway’s oldest rock found


Big smiles on the faces of Trond Slagstad and Harald Hansen after finding Norway’s oldest rock type. Photo: Rune Eian, NGU.
Analysis of the tiny grains of mineral zircon from gneiss in Finnmark reveals that this rock is over three billion years old. "It is fantastic that we have finally confirmed that rocks this old can be found in Norway. But, we can probably find even older rocks in Norway", suggest geologists Trond Slagstad from the Geological Survey of Norway (NGU) and Harald Hansen from the University of Tromsø (UiT).

"From the analyses we see that this rock was formed from magma that solidified 3,002,000,000 years ago. This means that it is Norway's oldest known rock", explains Slagstad and Hansen. "We found the sample south of the Lakselv in Finnmark. The previous "record" of this type is just under 3 billion years. Researchers also found that sample in Finnmark, which supports the hypothesis that the region is home to Norway’s oldest rocks. Hopefully, we find even older rocks in this area in the future", they add. 

The gneis laying where it was found in Finnmark. Resting on top of smaller rocks and the letters "103" written on it. Green gras in the background.
The gneiss was found south of Lakselv river in Finnmark. The rock is crushed, washed and polished so that the minerals can be more easily viewed. Photo: Harald Hansen, UiT. 
Many small samples of the mineral zircon in a microscope.
By analysing isotopes (elements which have a different number of neutrons) of uranium and lead in a small grain (ca 0.1 mm) of the mineral zircon, we can determine the age.  
Photo: NGU.  

Closer to the process that shaped the earth

The age of the planet Earth has been estimated to be ca. 4.6 billion years. Understanding more and more about old rocks gives us new knowledge about the evolution of Earth, from its formation to the present day. We want to know more about the natural processes that have shaped Earth and created the prerequisites for life. 

"If we go back one or two billion years, the geological processes that dominated back then are quite like those that are operating today. However, we are more uncertain about the conditions before that time. We know that the Earth's interior was hotter, which led to vertical motion due to convection (hot geologic material rises and colder material sinks). On the other hand, horizontal movements of crustal plates dominate on Earth today. By identifying and studying even older rocks, we can look forward to a better understanding of the Earth’s early history, they concluded", without stifling their excitement or their smiles. 

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