A new model explaining this mysterious process suggests the core was created as dribs and drabs of iron percolated inward from Earth's lower mantle, according to a study published Oct. 6 in the journal Nature Geoscience. The mantle is the viscous, rocky layer between the crust and Earth's iron core.
Definition of flash card. : a card bearing words, numbers, or pictures that is briefly displayed (as by a teacher to a class) usually as a learning aid.
card game, 1834, American English, of unknown origin, perhaps from the first element of German Pochspiel, name of a card game similar to poker, from pochen to brag as a bluff, literally to knock, rap (see poke (v.)).