Volcanic eruptions.
Carbon dioxide
When Carbon or any other organic compound udergoes combustion, carbon dioxide is produced alongwith a release of large amount of energy as heat. C + O2 = CO2
The ocean absorbs large amounts of atmospheric carbon dioxide, and is acidified thereby.
No, mercury does not have large amounts of carbon dioxide. Mercury is primarily composed of the element mercury (Hg) and does not contain significant amounts of carbon dioxide.
Sources of carbon dioxide are from the burning of fossil fuels from both cars and factories. Also, volcanic vents add a large amount of carbon dioxide to our atmosphere.
In the past 50 to 100 years, man has burned about one halve of all the oil which formed through the ages, plus large amounts of coal, lumber, and natural gas. This is the source of the carbon dioxide. It would be worse except the oceans absorbed some of the carbon dioxide increase.
The ocean absorbs large amounts of atmospheric carbon dioxide, and is acidified thereby.
Carbon dioxide is increasing in the atmosphere today primarily due to human activities such as burning fossil fuels, deforestation, and industrial processes. These activities release large amounts of carbon dioxide into the air, leading to higher concentrations in the atmosphere.
Decaying organic life emits a large portion. Naturally occurring fires also add a great amount of carbon dioxide. Natural respiration of animal life also gives off carbon dioxide. In total natural processes make up 94% of all carbon emissions.
Carbon Dioxide because without water you die and with carbon dioxide(concentrated in large amounts) you will have trouble breathing, or possibly die.
Assuming you mean "carbon dioxide", the atmosphere of Venus is made up mainly of carbon dioxide.
Coal is an abundant but dirty energy source. It releases large amounts of carbon dioxide and other pollutants when burned, contributing to air and water pollution.