The history of Mars is divided into four separate periods of time: Pre-Noachian, Noachian, Hesperian, and Amazonian. The Pre-Noachian period is the time period from 4.5 to 4.1billion years ago. It represents the time period between the formation of the Red Planet to the beginning of the Late Heavy Bombardment. Very little is known about this time period because geologic forces have reshaped the surface of Mars since that time. From 4.1 to 3.7 billion years ago, Mars was in the Noachian Period. This period of time was primarily categorized by the Late Heavy Bombardment, a period of time where debris from the formation of the solar system was literally bombarding the planets. It was during this same period on Mars that life began to take hold on Earth. Amazingly, it was during the Noachian Period that water likely began flowing in abundance across the Martian surface. It was also during this period that Mars is believed to have become habitable. Not only was liquid water present, the atmosphere was far denser and warmer than it is today. Furthermore, organics began to form in abundance in the Martian water. If life ever did arise on Mars, it would likely be during this time period. For the next 700-million years, Mars would remain a habitable world. However, things began to change during the next era: the Hesperian Period. Beginning 3.7 billion years ago and ending 3 billion years ago, the Hesperian was a very interesting time period for Mars. Massive floods were common in this era, as were volcanic eruptions. In fact, it was during this time period that the largest volcano in the solar system began to form: Olympus Mons. At 25 km in height, it is nearly three times higher than Mt. Everest. However, as the Hesperian came to an end 3 billion years ago, Mars was no longer the blue marble it once was. Its magnetic field was getting weaker, and as a result, it had no protection against the solar wind. Eventually, radiation from the sun stripped Mars of its once dense atmosphere. Temperatures began to plummet, its water either froze or was broken down by solar radiation. Interestingly, the magnetic field of Mars grew weaker due to a loss of internal heat, a direct result of the fact that smaller planets lose heat faster.

The surface of Mars is a fascinating place. Perhaps most fascinating is the fact that the surface is divided among two large regions called the Highlands and the Lowlands. The highlands exist in the Southern Hemisphere while the lowlands exist in the Northern Hemisphere. The two regions are very different from each other in terms of surface geology. The northern lowlands are characterized by vast smooth plains and volcanoes, while the southern highlands are characterized by a large number of impact craters. These differences suggest that, for whatever reason, the lowlands are of a younger age than the highlands. A smooth surface and a lack of impact craters suggests a history of geologic activity. Another explanation is that the Northern Hemisphere of Mars was impacted by a large, nearly planet-sized object around four billion years ago. If this is the case, the lowlands could actually be a single impact crater.

Like Earth, Mars is home to two large polar ice caps, one in the North Pole and one in the South Pole. The polar ice caps on Mars are about 70% water ice. The remaining 30% is a combination of frozen carbon dioxide and carbon monoxide. Like the polar ice caps on Earth, the Martian ice caps can grow and shrink depending on the season. During the summer, heat from the sun melts frozen carbon dioxide and carbon monoxide, which then return to the atmosphere. During the winter, these two gases become frozen and are deposited on the surface. The melting and freezing of gases in the Martian atmosphere also has an effect on the planet’s weather. The process of melting and freezing the polar ice caps transports dust and water vapor across the Martian surface, creating clouds, winds, and even dust storms.