To learn more about Norse colonization patterns, Hagelberg and her colleagues extracted teeth and shaved off small wedges of long bones from 45 Norse skeletons that were dated to between A.D. 796 and A.D. 1066. The skeletons were first unearthed in various locations around Norway and are now housed in the Schreiner Collection at the University of Oslo.

The team looked at DNA carried in the mitochondria, the energy powerhouses of the cell. Because mitochondria are housed in the cytoplasm of a woman’s egg, they are passed on from a woman to her children and can therefore reveal maternal lineage. The team compared that material with mitochondrial DNA from 5,191 people from across Europe, as well as with previously analyzed samples from 68 ancient Icelanders.