As the Sun's luminosity intensifies in the distant future, Earth's carbonate-silicate cycle will draw down CO₂ from the atmosphere, ultimately dooming land plants either by overheating or by CO₂ starvation. Previous estimates pegged the biosphere's remaining lifetime at around 1 billion years, but recent models with updated parameters have pushed that to 1.6–1.86 billion years. To explore how seafloor weathering and stochastic variations in CO₂ degassing rates affect this timeline, the model was extended. The results show: if the seafloor weathering feedback is stronger than the continental one and contributes significantly to global silicate weathering, the biosphere's remaining time could shrink, though it will likely still exceed a billion years. Stochastic fluctuations only matter if their amplitude exceeds the variability observed over the last billion years. The impact of weak seafloor weathering and low variability is negligible.
The Sun is slowly brightening, and in hundreds of millions of years its heat would become lethal for Earth. Fortunately, the built-in planetary thermostat — the carbon cycle — when overheating triggers rocks to absorb carbon dioxide faster, cooling the climate. The price of cooling is that plants lose their main source of food.
Scientists have recalculated the thermostat's operation, adding the effect of seafloor weathering (water eats away rocks, taking up CO₂) and random volcanic emissions. Results: even with aggressive gas sequestering by the ocean floor, greenery will persist for over a billion years. In a quiet scenario — 1.6–1.86 billion years, longer than previous estimates.
These numbers change our idea of the biosphere's shelf life and help search for life around other stars. The planetary thermostat can work on exoplanets with oceans and volcanoes, making them habitable for longer than thought.
🎯 The process of rock weathering that regulates climate was discovered only in the 20th century, though it has been operating for billions of years.
🎬 In Asimov's 'Foundation', scientists predicted the fall of civilization centuries ahead; here astronomers peer a billion years into the future of the biosphere.