of the sun and planets. This would not prevent the formation of gas giants farther out. I would give mars an initial composition linearly between Jupiter and Earth, based only on its orbital position. I liuke this simple theory. That would have given Mars a whole lot of gas to start with.

About the meteorites, you made me think. I have seen once before someone state as you did, that a thick atmosphere would cause all most all meteorites to burn up. At that time, I just accepted that statement. Now, I greatly doubt that this is true. On Earth, with its pretty miniscule 7 kilometer atmosphere, it is still sufficient to put the brakes on all meteorites up to a certain modest size (such as the Hohoba Farm meteorite), such that in the end, they basically fall out of the sky (usually cold) with almost no residual velocity. (I have a book showing this.) Those that do impact the Earth with residual velocity strike so hard that they are pulverized to smitherines, and no pieces are found except dust. With a thick atmosphere, then there would just be more meteorites that would reach their terminal velocity, and fall to the ground at lower speed leaving modest craters.

Have the people who study crater distributions used their data to estimate atmospheric thickness? This certainly seems possible to me