Explain why atmospheric components present in small quantities?

These three links might help :Earth's Atmosphere a href="http://www.visionlearning.com/library/module_viewer.php?mid=107" rel="nofollow"http://www.visionlearning.com/library/mo…/a ----------- Components and Characteristics of the Earth's Atmosphere a href="http://www.infoplease.com/ce6/sci/A0856758.html" rel="nofollow"http://www.infoplease.com/ce6/sci/A08567…/a ------------ Earth's Atmosphere a href="http://www.nasa.gov/audience/forstudents/9-12/features/912_liftoff_atm.html" rel="nofollow"http://www.nasa.gov/audience/forstudents…/a