Geology of the Northwest Territories province from dikes and mafic lava flows, overlain by deep ocean turbidite deposits. These rocks are believed to be the remains of oceanic crust that ended up preserved, surrounded on all sides by felsic volcanic rocks and granitoid plutons. In the area of Snofleld Lake in the northern part of the Slave Province, the remains of Archean stromatolites are preserved in a dolomite unit between felsic volcanic and greywacke-mudstone turbidites, some of the earliest evidence of life, forming in the shallows around volcanic islands. Around 1.27 billion years ago in the Proterozoic, a series of major magmatic events affected the
Continental crust lower continental crust, which is more mafic in character. The continental crust consists of various layers, with a bulk composition that is intermediate to felsic. The average density of continental crust is about 2.7 g/cm, less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm. Continental crust is also less dense than oceanic crust, whose density is about 2.9 g/cm. At 25 to 70 km, continental crust is considerably thicker than oceanic crust, which has an average thickness of around 7–10 km. About 40% of Earth's surface is currently occupied by