Final answer:
The Martian atmosphere is composed of approximately 95% carbon dioxide, significantly higher than the Earth's current level which has risen above 400 ppm due to industrial activity.
Step-by-step explanation:
The percentage of carbon dioxide that makes up the Martian atmosphere is approximately 95%. This is vastly greater than Earth's CO2 levels, which even after industrial increases are well below 1%. The Martian atmosphere is composed primarily of carbon dioxide, with about 3% nitrogen and 2% argon. Earth's atmosphere pre-industrial CO2 levels were at 280 ppm and have risen above 400 ppm, which is a concerning increase for our climate. However, this is still a fraction of the Martian atmosphere's composition. In comparison, Mars' atmospheric conditions pose a significant challenge for any potential terraforming efforts due to the high concentration of CO2 and the lack of infrastructure on the planet.