re: While the "always frozen" Mars scenario
I've always suggested a commonality between Mars and bodies in the outer solar system, not the inner.
Mars is a warmed-up giant asteroid, not a cooled-down small Earth.
I think we can learn a lot about asteroids like Ceres that were large enough to differentiate and have lava flows and even free water (ice), if we apply cold Mars models to their evolution.
The Early Earth is a puzzle. We don't fully understand what sort of atmosphere it had, other than knowing that it must have been an effective greenhouse to allow liquid water so early on when the Sun was cooler.
We're still learning about planets and solar systems. It helps to keep a sense of perspective, as Zaphod Beeblebrox said...