The cycles within which earth's matter moves are closed systems. This means nothing is gained or lost from the system; it only changes from one form to the other. The total amount of matter on earth remains the same. Using tectonic plates as an example, divergent boundaries occur where new oceanic crust is being created. New crust is being created and simultaneously the same amount of crust is being destroyed at convergent margins.
Doldrums, also called equatorial calms, equatorial regions of light ocean currents and winds within the intertropical convergence zone (ITCZ), a belt of converging winds and rising air encircling Earth near the Equator.
