Venus, Earth, Mars - same initial conditions?

sneez · Venus, Earth, Mars - same initial conditions?

I am learning about other planet's evolution and their atmospheres. It is the foundation of basically any study on this topic, that all three planets started with the same exact (to a negligable degree of difference) conditions. The most important of all, it is assumption that the initial amount of water on all 3 planets was the same. I found this assumption very hard to over come.

I know about the D/H ratio of mars, earth and other supposed evidence of this assumption being true, but its not strong evidence to me. I just dont see the necessity of this being true, given all the different geophysical factors.

Anybody with more knowledge on this? opinion?