Earth, Cooling Down, after ~4.5billion years

Approximately 4.5 billion years ago the earth was nothing more than a giant blob of lava. Fast foreward a little and you find the modern earth, consisthing of an outer crust, and outer mantle, a mantle an outer core and a solid iron core.
The induction process of earth's tectonic plates means that magma from the earths intereor is pushed to the surface and cooled. then it is sucked back in sometime later, meaning that the earth is gradually cooling.
I am still unclear on the procesese of the earths magnetic feald and its effect on life on earth, but I have been told and shown in many mathmaticall calculations that I cant even begen to wrap my left-brain mind around, that the earths magnetic feild is the only thing between us and DOOOM!
If the earth cooled down would it be a minor inconvenience or a doomsday scenario?

-Roan

Mars was as Earth is now
it has cooled and expanded... it will disintigrate in the future to become rubble

the same fate awaits Earth.

I propose we put up a constellation of giant mirrors into Earth orbit to reflect additional solar radiation to the surface and warm the planet.

You can't reheat the Earth in any practical way by shining light on the outside surface. If it was possible to do so Mercury would not have cooled down.

My assumption is that planets start out as star formations. This ties in into ball of lava of accumulated matter around multiple vortexes aka planets. One could conclude the order of formation by looking at planets sizes. the idea being that all vortexes were accumulating matter from the same cloud. Sun being the first to form and say Saturn and Jupiter second and third and so on. Size may not be the only clue as to which came first in the solar system but i think the idea is clear.
One of the things you notice when you look at the pictures from universe is clouds and stars. Basically there are only stars to be seen. Clusters of stars in a larger vortex. Thus the implication that whatever is happening in universe kind of ends up as a star or something in in-between stages like planets. Now i am not referring to death of stars but to birth of stars which i assume is the same exact process resulting in formation of a planet. Thus mass and cooling effects being different.
I dint believe in matter accumulation from rock clumping because if that were real then an asteroid belt should gradually become a planet OR Saturn's rings would gradually form a planetoid. That is obviously not happening.
This additionally means that all types of substances we see on earth may have originated in the very process of earth formation as some kind of transmutations of matter. For example IF iron can be liquefied at room temperature as supposedly demonstrated in one of Hutchinson effects then we would be talking about strong magnetic fields and very high frequency oscillations which allow for such things to happen.