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.
Among other things, ocean currents are responsible for the warmer temperatures in Western Europe, they enable the Antarctic to support vast amounts of plant and animal life and their disruption likely caused a mass extinction of 95 percent of all marine life 250 million years ago [source: NOAA: Ocean].