Let's say you have a fast-moving object in space and two points on opposite ends of the earth, one which is currently carried by earth's rotation towards it, and one away. If the scale of time dilation depends on relative speed, then the two points on Earth should have different relative speeds and thus time, however you'd expect their time to be the same. In a short time frame that system would be more or less inertial, no? This is something I never understood

Mars is in fact supposed to have been a water world.

I have zero information on this myself, but wikipedia says "The volcano's outer edge consists of an escarpment, or cliff, up to 8 km (5.0 mi) tall (although obscured by lava flows in places), a feature unique among the shield volcanoes of Mars, which may have been created by enormous flank landslides."