Final answer:
Mars differs from Earth in terms of its size, atmosphere, and geological activity. It had a thick atmosphere and seas of liquid water in the past, conditions associated with the development of life. Currently, Mars has a harsh and inhospitable environment.
Step-by-step explanation:
Mars differs from Earth in terms of its size, atmosphere, and geological activity. Mars is smaller than Earth, with a mass only 0.11 times the mass of Earth. While Mars retains a thin atmosphere and has experienced considerable geological activity in the past, its most significant difference is that it probably had a thick atmosphere and seas of liquid water in the past, which are conditions associated with the development of life. Currently, Mars has a harsh and inhospitable environment, making it different from Earth.