Kenorland


Kenorland is a supercontinent postulated to have existed between about 2.72 and 2.45 billion years ago. Zircons found in the core of the supercontinent (what is now the Canadian Shield) have been dated to be about 3.2 billion years old. Greenstone belts in the vicinity of the Yilgarn Craton (in Western Australia) are dated to a similar age.

It is thought that the creation of land back in those days proceeded from a deep mantle plume rifting that caused relatively rapid circulation of materials from the hot core of the planet to the cool surface, and back again. The core of Kenorland came together around the junction of the Laurentia, Baltica, Western Australia and Kalaharia cratons and most of the Nena craton. Kenorland was draped across the equator, existing mostly in the low latitudes until the supercontinent began to break up. At the end, the breakup happened at the juncture of the land masses between the supercraton clusters at the eastern and western ends of the supercontinent. Further, some of those supercraton clusters also broke up with the Kola craton (western Scandinavia) separated from the Karelia craton (eastern Scandinavia) by about 10° of latitude.

The breakup of Kenorland is postulated to also have been the time of a changeover in the core of the Earth as deep mantle plume rifting gave way to the two-layer core-mantle plate-tectonics-convection theory we hold now. The breakup of Kenorland at around 2.5 billion years ago coincides with the geological change from the Archean Eon to the Proterozoic.

It is postulated that the beginning of the Huronian Glaciation (about 2.5 billion years ago) coincided with the atmospheric changeover from mostly methane and carbon dioxide to a significantly higher level of oxygen. That atmospheric change increased continental rainfall, which accelerated the decrease in the amount of carbon dioxide. With solar radiation levels about 85% of what they are today and drastically reduced greenhouse gases in the atmosphere, Earth plummeted into the Snowball Earth scenario that lasted for about 300 million years.

The minor supercontinent Arctica was one of the major pieces left after the breakup of Kenorland. About 2.5 billion years ago Arctica was comprised of the North Atlantic, Slave, Superior and Wyoming cratons of Laurentia plus the Angara craton of Siberia.

A second minor supercontinent of the time was West Gondwana, composed of what is now South America and Africa. East Gondwana was composed of India, Antarctica, Australia and North China.

About 2.1 billion years ago the continental land masses of the planet were coming back together again to form the supercontinent Columbia.

The cratons of West Gondwana
The West Gondwana cratons about 1.8 billion years ago
Map modified to show relationship to modern continents
Bottom map courtesy of Wikipedia userid Woudloper, CCA-by-SA 3.0 License