The human settlements hierarchy is as follows: - An ecumenopolis is a theoretical construction in which the entire area of Earth that is taken by human settlements, or at least, that those are linked so that to create an urban areas so big that they can shape an urban continuum through thousands of kilometers. - A megalopolis is a group of conurbations, consisting of more than ten million people each. - A conurbation is a group of large cities and their suburbs, consisting of three to ten million people. - A metropolis is a large city with it's suburbs, consisting of multiple cities and towns. - A large city is a city with a large population and many services. - A city has many services, but not as many as the large city. - A large town is a town with population of 20,000 to 100,000 people. - A town has a population of 1,000 to 20,000 people. - A village is a human settlement or community that is larger than a hamlet but smaller than a town. - A hamlet has a very small population, very few services, and only few buildings. - An isolated dwelling has only 1-2 buildings.
The youngest age of the shale is 910 ka. According to the principle of inclusions, the shale formed before the tephra, so the tephra must be younger than 910 ka.
