Has the coastline changed?
The vast area covered by these mounds shows how significant this erosion was. “The boundaries of the binary have receded by hundreds of kilometers,” the researchers say. “On the western side of the Ares Valley alone, nearly all the interstitial material, approximately 57,000 cubic kilometers from an area of 284,000 square kilometers, was removed, leaving only debris.”
Based on the distribution of different clays, the research team argues that those clay formations were formed by water before erosion of the material. This indicates that water-rock interactions were occurring over a very wide area early in Mars’ history, likely requiring an extensive water cycle on the Red Planet. As the researchers point out, the region would have been more likely to be exposed to water if there was an ocean nearby, but that exposure was likely due to processes such as melting at the base of the ice sheet. There is a possibility that there is.
Further complicating matters, many of the mounds are located below one proposed coastline in the North Sea and above a second. Receding oceans may have contributed to their erosion. At the same time, however, some of the proposed coastline features are thought to have resulted from general erosion of the original plateau and may not be associated with the ocean at all.
Overall, the new results provide mixed evidence for the existence of an ocean on Mars. These clearly indicate active water circulation and extensive erosion, both consistent with large amounts of water in the surrounding area. At the same time, however, the water exposure experienced by the mesas and buttes need not result from submersion into the ocean and, given their elevation, may be best explained through some other process.
natural earth science2019. DOI: 10.1038/s41561-024-01634-8 (About DOI).
