People think Earth dies when the Sun becomes a red giant in five billion years — the more likely end is a billion years from now, when a star already 30 percent brighter than at birth pushes CO₂ too low for C3 plants, then a moist greenhouse strips the oceans of hydrogen and leaves a sterile Venus

The Sun is roughly 4.6 billion years old and about halfway through its main-sequence lifetime. The popular conception holds that Earth’s destruction will come when the Sun becomes a red giant roughly 5,000,000,000 years from now, but Earth may become uninhabitable billions of years before that—not because of a sudden solar catastrophe, but because of the normal evolution of an…