Anthropogenic increase in the length of a day
The length of a day might have been increasing owing to decreased speed of the earth's rotation triggered by anthropogenic factors: 1) anthropogenic induced increase in the moment of inertia of the earth; and 2) slowdown of tidal currents due to impediment by artificial structures. The 1st factor would arise if humans move natural resources (e.g., metals, oil) from under to above the earth's surface, which results in increased distances between these resources and the center of the earth, namely, the moment of inertia. The 2nd factor would arise if humans weaken the tidal currents by building structures in the sea (e.g. dykes) and by performing tidal power generation. These possibilities can be tested by examining how humans have been utilizing underground natural resources and effects of manipulations of the flow in the sea. In addition, it may be useful to monitor the precise length of a day in future.