Earth's magnetic field, atmosphere, and Theia impact.

I was thinking of the question of life on Earth verses on Mars. Mars has had its atmosphere stripped away by the solar wind, while Earth has not, due to its magnetic field.

The Earth still has a molten core due at least in part to radioactivity.

I'm aware that there is circulation in the crust of the Earth that helps bring radioactive elements deeper into the mantle from higher levels and that this circulation is driven by heat.

Is is possible that were the Earth never hit by Theia, (a hypothesis) it would have by now cooled to the point that there would be little or no circulation in the crust? What I'm saying is that the early Earth may have had it's radioactive elements widely distributed within its crust, leading to a faster loss of heat than if those elements were concentrated in the core.

Is it possible that the impact caused radioactive elements, which previously were distributed throughout the crust, to be concentrated in the core and also combined there with any radioactive elements present in Theia? This impact could have initiated or enhanced the circulation in our crust today.

What if, by now, the Earth's atmosphere would have been stripped away if not for that impact? If that were the case, there would be no life as we know it upon Earth.

Could this unlikely (less likely?) event be the reason there is complex life on Earth, but not commonly elsewhere in the universe?

Maybe in most places that life can begin, it does, but then is extinguished by the stripping of the atmosphere by the nearby star?

Armchair philosophy, I know, but I'm curious if this has ever been proposed. It seems like an obvious thought.

Maybe James Webb will tell us if atmospheres around (Earth sized) exoplanets are common or not...