When Hynek and Phillips studied the MOLA data, they noticed that western Arabia Terra looked different than the nearby highlands. Unlike the heavily worn highlands, western Arabia Terra has very few large craters and traces of erosion. The elevation there is also about a kilometer lower than that of the southern highlands. According to Hynek, the most likely erosional force of this magnitude is flowing water. Lots of things can erode planets.
Wind is very effective on long timescales.
But on this large of a scale these are unlikely explanations. The researchers estimate the erosion of Arabia Terra took place early in martian history and ended 3.5 to 3.8 million years ago. This time period coincides with datings of other fluid features and a time when martian volcanoes were quite active. Employment Copyright 1996-2001 Kalmbach Publishing Co.