Re: venus anyone
The Wikipedia article does explain it. In the absence of tectonics and subduction there's no method of removing the carbon dioxide and a lot of the water, which on Earth end up in rock (what's limestone? There are whole mountain ranges made of it, e.g. the Dolomites). Result is runaway greenhouse effect. Hydrogen gets knocked off by solar wind, carbon dioxide is too heavy and stays more or less put. Result is a planet where a lot of the hydrogen is deuterium and there is no mechanism for removing the carbon dioxide.
Plate tectonics and early plants did such a thorough job that we ended up with the snowball Earth, and it's hypothesised that only the eruption of really large volcanoes repopulated the atmosphere to allow warming to restart. There is no guarantee that any set of initial conditions will not end up at an extreme rather than comfortably in the middle.