Billions of years ago, Mars and Venus were habitable worlds. They had oceans, atmospheres, maybe even primitive life. However, as the Solar System evolved, Venus was scorched by fire and Mars was frozen to death. Only earth survived, thanks to its position in a far more stable part of the Solar System. What happened? Well, back then, the sun was much colder. Therefore, Venus, which is now too close to the Sun to support life, was in just the right place to become an earth-like world. Mars had a much thicker atmosphere back then, and so heat was trapped inside the atmosphere, warming the planet. Earth had much greater volcanic activity at the time, so it was well warmed. However, as the Sun expanded, Venus grew too hot and its oceans evaporated. Mars too was affected, for solar winds from the sun blasted away its atmosphere. Earth had a stronger magnetic field than Mars, which repelled the deadly solar winds. And it was farther from the Sun than Venus, so it wouldn't become overheated. As the Earth aged, volcanic activity went down, and the Earth settled into the perfect equilibrium. But could things have been different? Supposing that Venus and Mars had somehow survived, what would the solar system look like today? what would have changed? What strange creatures, what amazing events, what mighty landscapes, what amazing worlds would the Three Earths have been?
That's up to you. This being an open timeline, it is your job to make sure that it succeeds. You can create the new Venus, the green Mars and the beautiful Earth. Just remember, you must remain plausible, and I decide what goes and what stays. Someday, this article will be worthy of being a Featured Article. Until that happens, research the planets and create an althistory to be proud of. Good luck!
Point of Divergence
If somebody has an idea as to what POD could save both Venus and Mars, put it in the talk page. I will try to confirm or deny them later. Get somebody from Space Wiki down here...