The atmosphere of Mars is thin and composed mainly of carbon dioxide, making up about 95% of its composition. It also contains small amounts of nitrogen, argon, and oxygen. The low atmospheric pressure, less than 1% of Earth's, means that liquid water cannot exist on the surface for long periods. Mars experiences extreme temperature variations, ranging from about -195°F (-125°C) at the poles during winter to 70°F (20°C) at the equator in summer. Dust storms are common and can cover the entire planet, affecting visibility and temperature. The thin atmosphere also allows more radiation from the sun to reach the surface.