a mix of Venus and Titan

Hi

I am imagining a planet. And I have some questions (in bold)

Let us imagine a planet slightly smaller than the Earth, as Venus or else smaller. Bigger than Mars, to remain geologically active.

As on Venus, the water does not remain liquid, greenhouse effect accelerates.

Let us imagine now that the cloud cover of ice crystals forms more quickly than on Venus, and especially let us imagine that it is more spread. She would block the sunlight and greenhouse effect goes down with time.

The temperature goes down to surface, but not pressure: without tectonics of plates, the carbon dioxide is not recycled. With a lower temperature than the one who reigns over Venus, a part of the carbon dioxide becomes liquid.

I wanted to know if it was possible that the (liquid or gaseous) carbon dioxide reacts with the water (gaseous) to form some methane.

This methane would go back up in the high atmosphere and react with the solar ultraviolet rays to form composite complexes (as on Titan), which would fall again to the surface and to dissolve in the liquid carbon dioxide.

I know that the supercritical carbon dioxide is a very good solvent. Is he also for the liquid carbon dioxide?

Life can her appear in this oceans? They have all that is needed: complex organic molecules, solvent, sources of energy (volcanoes)...

One would get so an orangy planet as Titan, but different in its surface.

Hard to say , as we only know for certain one (albeit varied) example of life. But let's go at it for the fun of it.

The complex molecules would follow a gradient on the diferences of presure and avaiability of the diferent components , energy flow and local boundaries.

Leaving aside the obviusly diferences in solvents , i suppose i would be looking for the start of life not in the supercritical CO2 nor in the upper atmosfere , but in the interfaces between the mediums , like the lakes and rivers , in steep slopes on the surfece , or even caves below semi-active volcanoes.

As for the physical makeup of life , such solvent and presures begs for a really thougth protection , so a silica exterior / bones /fibers seems like the way to go for living tissue to grow.

If we add Sulfur as another building block on that enviroment , i would bet undercarbondioxide (cannot call it underwater , can we? ) volcanoes would be like an ideal spot to startup some experimental life as we don't know it

Local deposits of oxidized ores (Mn/Fe/Ag/Ni) or complex salts deposited by the local fumes may be all you need to form complex pseudo-organic chains

For a more complex setup , we would do good to asume that no single form of life lives alone. There is a chain of predator/prey and mutual cooperative lifeforms that exchange their byproducts of heavy specialitation , like sulfur extractor living side by side with oxigen removers feeding S02 hidrogenators with are preyend upon H2S04 feeders. Complex enzymatic process are like that.