translation.en: We believe that the oceans were in the northern hemisphere, and this area in blue, which shows a depression of about four miles, was the ancient ocean area on the surface of Mars.
translation.zh: 我们认为海洋曾经位于北半球。 这些蓝色区域 显示的是约4英里的深度， 曾经是火星表面的 古海洋区域。