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.
A variant, found in electronic flashcards, is what is known as a three-sided card. This is a particular kind of asymmetric two-sided card; abstractly, such a card has three fields, Q, A, A*, where Q & A are reversed on flipping, but A* is always in the answer â the two sides are thus Q/A,A* and A/Q,A*.