Points have all ready been discussed.
Also, it won't work the other way around. The learning comes from comparing the two planets. For example, Mars. WE may very well be witnessing the dawn of life on Mars! This generation, or the next will never see anything come to fruition of course, but it is very possible that we will soon have Prokaryotes on Mars! Then, they will reproduce until something mutates, and we have Eukaryotic cells, then small multi-celled organisms, and in a few...million years, creatures! By studying the planet now, we may be able to fill in the blanks on our own history. We couldn't do this via our own planet (not completely) because it's all ready happened, but now we have an Opportunity via Mars.