Some of the oldest rocks in the world are found at Isua, north-east of Nuuk, the capital town of Greenland. Here the mountains contain 3.9 billion-year-old rocks that have been intensively investigated by geologists, and which contain the earliest signs of life on Earth in the form of carbon thought to be produced by micro-organisms. Evidence has also been found for plate tectonic processes even at this early time. The ancient rocks around Isua are bounded by younger crust formed 2.5 billion years ago, with to the north and the south still younger rocks formed 1.8 to 1.6 billion years ago. The bedrock between Kangerlussuaq and the inner part of the Disko Bugt region, comprises both 2.5 billion years and 1.8-1.6 billion years old rocks that were formed deep down in the Earth’s crust.
Together with North America, Greenland formed a large North American continent, 1.6 billion years ago. At that time the folding in the Precambrian mountain ranges in Greenland was more or less complete, and the shield had risen and was partly eroded. Later developments largely involved the marginal parts where rocks formed later are preserved in North Greenland, East Greenland and parts of central West Greenland. Two large fold belts were formed along the coasts of North and North-East Greenland 400-350 million years ago.
Greenland’s subsequent geological development was dominated by the formation of sedimentary basins along the margins of the Precambrian shield, where 5-10 kilometre thick successions of sediments were deposited. These deposits are preserved today in coastal areas, with the thickest successions offshore on Greenland’s continental shelf. The sedimentary rocks on Disko, and the peninsula of Nuussuaq north of Disko Bugt, were formed 120-60 million years ago. The rock types include deposits from rivers and lakes and marine sediments deposited off the then coast.
Tectonic plate movements 60-55 million years ago led to the opening of the Atlantic, when Greenland was separated from Norway and northern Europe. Meanwhile the Labrador Sea and Davis Strait resulted from movements along a spreading axis between Canada and West Greenland. Sea-floor spreading was accompanied by profuse volcanic activity along the rupture zones, and the resulting km-thick volcanic successions are preserved today on Disko, Nuussuaq and Svartenhuk Halvø in West Greenland, and in the central part of East Greenland. Similar lava-successions are widespread on the sea floor offshore West and East Greenland.