Although the overall geologic character of Mars is unique in the solar system, it shares characteristics of both the Moon and Earth. This comes as no surprise, because Mars is similar in composition to both bodies. What does come as a surprise is the immensity of many geologic features on Mars compared with the same kinds of features on Earth. The size can be explained by the apparent lack of plate tectonics on Mars, which tends to relocate centers of mountain-building activity, and by the planet's less erosive atmosphere and climate. Another major difference between the two planets is the catastrophic flooding that has occurred on Mars when its abundant groundwater was released in great volumes.

Although the overall geologic character of Mars is unique in the solar system, it shares characteristics of both the Moon and Earth. This comes as no surprise, because Mars is similar in composition to both bodies. What does come as a surprise is the immensity of many geologic features on Mars compared with the same kinds of features on Earth. The size can be explained by the apparent lack of plate tectonics on Mars, which tends to relocate centers of mountain-building activity, and by the planet's less erosive atmosphere and climate. Another major difference between the two planets is the catastrophic flooding that has occurred on Mars when its abundant groundwater was released in great volumes.