Answer:
All they are missing is a source of water. While 78.1% of Earth's atmosphere is nitrogen, Mars is only 1.9% nitrogen-based. Earth is rich in oxygen (20.9%).
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How is Mars' atmosphere different from Earth's?
Dominant Gases Mars Earth
Carbon dioxide (CO2) 96% 0.0391%
Nitrogen 1.9% 78.1%
Oxygen 0.174% 20.9%
Argon 1.9% 0.93%