The most dense greenhouse gases on the earth are $\mathrm{CO}_{2}, \mathrm{CH}_{4}, \mathrm{O}_{3}, \mathrm{CFCs}$ and water vapor.

These gases are found on the earth's surface.

The absorbed solar energy emits from the atmosphere of the planet and the result is that

atmosphere becomes warm.

Greenhouse gases are important to maintain the earth's atmosphere.

If there is no greenhouse gases, then the earth's average temprature decreases and makes it unfit for living so life on earth will not be possible.