Formation and early history

Summary

Mars formed along with the other planets about 4.5 billion years ago. Its early geological record is commonly divided into major periods, beginning with the Noachian period (roughly 4.5 to 3.5 billion years ago), when the surface was heavily shaped by meteor impacts and valley formation, along with erosion and evidence consistent with possible water oceans. During this early era, Mars also experienced the loss of its magnetosphere, which would have affected its ability to retain an atmosphere. In the following Hesperian period (beginning about 3.5 billion years ago and ending roughly 3.3–2.9 billion years ago), Mars’s history was dominated by widespread volcanic activity and flooding. These processes carved large outflow channels across the planet. The Amazonian period, which continues to the present, is characterized by the remaining influence of earlier geological processes and ongoing, more subdued geological activity.

Key Points

• 1

  Mars formed about 4.5 billion years ago and its early surface history is dominated by major geological periods.

• 2

  Noachian (4.5–3.5 billion years ago): heavy impacts, valley formation, erosion, possible water oceans, and loss of the magnetosphere.

• 3

  Hesperian (3.5–3.3/2.9 billion years ago): widespread volcanism and flooding that produced immense outflow channels.

• 4

  Amazonian (to present): current-dominating geological processes continue under the influence of earlier history.