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.
Currents and Marine Life Currents are powerful physical forces in the seas. They move water and heat around the globe, and help determine the chemical make-up of the water column.