Geological History of Mars

Like Earth, Mars also has had a diverse geologic history. The surface of Mars has been affected by volcanism and the action of wind, water and ice. The heavily cratered surface of Mars preserves the evidence of events of the planet's earliest history. Rock units formed in this early period show the scars of being battered by the still-numerous impacts that followed the formation of the Solar System. The history of the low northern plains is not preserved from this period, perhaps, because they were carved out by an enormous impact.

Throughout the planet's ancient history, volcanic activity had taken place. This has resulted in the formation of extensive lava plains in Mars. A large part of the volcanic activity has been in Tharsis and Elysium. Huge floods of water have periodically flowed across the surface, some being triggered in some way by volcanism.

Close-up of Tharsis

One of the most intriguing aspects of Martian geology is the role that water has played in the evolution of the planet. Although there is abundant evidence of water erosion, liquid water is unstable at the surface of Mars under present conditions. The scale of the erosion suggests that large floods once occurred in Mars. Some of these floods would have had discharges one hundred times the annual outflow of the Mississippi river.

Climatic History of Mars

Mars' history was dominated by the effects of internal heat loss. The many stream valleys seen in the ancient cratered highlands, formed before 3.5 billion years ago, indicate that a warmer, thicker atmosphere probably covered Mars at that time and may have allowed at least occasional occurrences of precipitation and surface runoff.

The internal heat loss led to extensive volcanism and tectonism at the surface. This led to sudden releases of huge stores of millions of cubic kilometers of ground water, carbon dioxide (CO₂), and sulfur dioxide (SO₂). The change in climate around 3.5 Billion years ago may have been caused at least in part by these sudden releases. These would have enhanced a greenhouse effect on early Mars.

Province of Tharsis - Long-shot

Mars and Earth – A comparison

Although, Mars is a planet on which most of the geologic processes familiar to us here on Earth have operated, the two planets are very different. The lack of plate tectonics on Mars has led to greater stability of the surface and to accumulated development of enormous volcanoes and canyons. In addition, the ineffectiveness of water erosion in eliminating relief has led to almost perfect preservation of features widely ranging in age. However, in spite of the near-perfect preservation, the origin of many of the features remains vague.