WeknowmoreaboutthesurfaceoftheplanetMarsthanweknowabout...
问题详情：WeknowmoreaboutthesurfaceoftheplanetMarsthanweknowaboutwhatisatthebottomofEarth'soceans.Untilrecently,scientistshadmappedonlyabout20percentoftheseafloor.Butourknowledgeofthedeepseasischanging...