Fill in the Blanks Greenhouse Gas: DefinitionsOnline version Let's match the terms with their definitions. They are all terms that are in the article you are about to read. Remember to start from the top and work your way down because when you click a word, it will automatically go to the next available space. by Marietta Chela 1 purify atmosphere convert biogas dioxide recycle 1 . A colourless , odourless gas produced by burning carbon and organic compounds and by respiration is known as carbon . 2 . Gaseous fuel , especially methane , produced by the fermentation of organic matter is known as . 3 . The envelope of gases surrounding the earth or another planet is known as the . 4 . To remove bad substances from something to make it pure is to . 5 . To use a special industrial process in order to make materials and products ready to be used again is to . 6 . To ( cause something or someone to ) change in form or character is to .