> 600 million : As weathering of Earth's surfaces increases with the Sun's luminosity, carbon dioxide levels in its atmosphere decrease. By this time, they will fall to the point at which C3 photosynthesis is no longer possible. All plants which utilize C3 photosynthesis (~99 percent of species) will die.

Interesting. We should save up our fossil fuels and burn them all at once in 600 million years to save the trees!

But in all likelihood, a lot of new fossil fuels will have formed by then.