There were instruments to measure the composition of the atmosphere of Mars as it entered the atmosphere.

NPR: Revisiting the Viking Missions to Mars

But the strength of the greenhouse effect depends on the chemical composition of the atmosphere, because the phenomenon is due to the absorption of infra-red radiation by various gases in the air.

ECONOMIST: Climate change: Getting real | The

Weather is caused by disturbances within the atmosphere, but climate is controlled by external influences, such as the distribution of oceans and continents, the extent of ice and snow-cover, variations in the amount of energy from the sun, and changes in the chemical composition of the atmosphere.

BBC: Time to spend more money preparing for colder winters?

The once-secret lives of plants are telling researchers volumes about the composition of Earth's atmosphere, providing clues to past and current climate change.

CNN: Plants spread secrets about climate change

"The text of the Clean Air Act makes plain that Congress intended it as a measure to 'clean' the air of pollutants, not to alter the overall composition of the Earth's atmosphere, " argues the Alliance of Automobile Manufacturers, an auto industry lobbying group, in a brief.

FORBES: Supreme Court Takes On Global Warming?

Team chemistry is an imprecise composition, and rules by themselves cannot ensure an atmosphere.

WSJ: Jason Gay: Red Sox Now Order Shirley Temples