In geology, what is the difference between a platform, shield, and craton?
Geologists analyze the Earth’s crust in detail to determine its composition, age, and tectonic history. One important distinction they have made is between the Precambrian (> 542 million years old) crystalline igneous and high-grade metamorphic basement making up the continents, called a shield, and an extensive sedimentary layer covering some areas of the shield, called a platform. Together, platforms and shields make up a craton, which is the foundation for a continent. One example of a shield is the Canadian Shield, which underlies modern-day Canada. Continents and cratons are not exactly the same thing. For instance, the island New Guinea, just north of Australia, is part of the Australian craton, but not part of the Australian continent because the strait between New Guinea and the mainland is currently flooded. During the last Ice Age, this strait was dry, and both bodies of land were part of the same continent. A shield is specifically an exposed area of Precambrian igneous or m
