The most important greenhouse gasses are the carbon dioxide and the evaporated water. These two are responsible for controlling the climate on Earth, and make a place suitable for life.They partially capture the heat from the sun and keep it around the low layer of the atmosphere around the Earth. If it wasn't for them, the heat from the Sun will come to the surface, but there will be nothing to stop it from getting back into the space, so the Earth will warm up, but than will cool of so much that it will be freezing and the temperatures will go around -70/-80 degrees, and this will be a daily cycle, so the Earth will become similar to Mars.