Scientists think that the climate on Mars is 3.5 billion years ago was similar to that of early Earth: warm and wet. But because of chemical reactions between Mars’ carbon dioxide was used up forming carbonate rocks. Mars atmosphere is very thin, the temperature is very cold, and what water remains is either frozen in the Martian poles as permafrost or hidden in deep underground springs. Mars’ current climate changes drastically during the year. The seasons in one hemisphere (South) are more extreme while in the other (North) they are less extreme. The temperature on Mars may reach a high of about 70 degrees Fahrenheit at noon, at the equator in the summer, or a low of about -225 degrees Fahrenheit at the poles. In the mid-latitudes, the average temperature would be about -50 degrees Celsius with a nighttime minimum of -60 degrees Celsius and a summer midday maximum of about 0 degrees Celsius. On Mars, the air is saturated (100% humidity) at night, but undersaturated during the day. This is because of the huge temperature difference between day and night. Occasionally, winds on Mars are strong enough to create dust storms that cover much of the planet. It can be months before all of the dust settles. The maximum wind speeds recorded by the Viking Landers in the 1970’s were about 60 miles an hour with an average of 20 miles per hour. In Mars’ northern mid-latitudes, wind blows from west to east. Mars’ average air pressure is 0.224 inches of mercury.