Quotation marks, also called 'inverted commas', are of two types: single and double. British practice is normally to enclose quoted matter between single quotation marks, and to use double quotation marks for a quotation within a quotation:
The oceans absorb the sun's heat, transferring it to the atmosphere and distributing it around the world via the ever-moving ocean currents. This drives global weather patterns and acts as a heater in the winter and an air conditioner in the summer.
The importance of migration. Migration plays an extremely important role in the survival of the blue whale species. It allows these marine mammals to feed in highly krill populated areas during their feeding season so that they can develop the thick layer of blubber they need to make their long migration trip.