Earth’s Complex Life Could Endure 500 Million Years Longer Than Anticipated

The sun is gradually getting brighter and expanding as it ages, eventually cooking the Earth before consuming it entirely. However, new research indicates that complex life may endure in this extreme Earth scenario far longer than previously estimated.

Observations of other stars suggest that our Sun will transition into a red giant in about 5 billion years, raising questions about how long our planet will remain habitable. In ecological terms, the final survivors of complex life will be the trophic biosphere, including plants both aquatic and terrestrial. Their survival heavily relies on Earth’s temperature and the crucial carbon dioxide levels essential for photosynthesis.

“The greenhouse effect acts as Earth’s thermostat, balancing CO2 levels to maintain a habitable temperature,” explains Jacob Haq Misra from Blue Marble Space in Washington. As temperatures rise, CO2 is absorbed into rocks, diminishing atmospheric levels and allowing some heat to escape.

This shift implies that as the Sun expands, CO2 will become the critical limiting factor for plant life. Previous estimates indicated that a threshold of about 10 ppm of CO2 in the atmosphere is necessary for plant survival; below this level, plants perish, leaving only microorganisms. This phenomenon is expected to occur roughly 1.35 billion years from now. While the exact longevity of these microbes post-plant extinction is uncertain, it is likely they will survive much longer.

Innovative simulations by Haq Misra and his colleague Eric Wolf suggest potential plant lifespans may be extended by an additional 500 million years. Their more sophisticated simulations account for specific plants, such as cacti and pineapples, that utilize a unique type of photosynthesis known as Crassulacean acid metabolism, which allows more efficient CO2 absorption. This could lower the CO2 starvation threshold to just 1 ppm, enabling the trophic biosphere to thrive for more than 1.8 billion years.

“Life on Earth is capable of much more than we might expect,” states Haq Misra. Over such extensive timescales, evolutionary adaptation could allow life to persist even longer, adjusting to the gradual warming triggered by the Sun’s expansion.

“These models suggest that we may be on the brink of understanding Earth’s complex biosphere, rather than approaching its end, as previously pessimistic scenarios suggested,” shares Edward Schwieterman from the University of California, Riverside. This insight is promising, as it implies that if we treat Earth as a representative example of a habitable world, our chances of discovering biospheres on other planets may be higher than previously anticipated. “This isn’t merely a philosophical query; it has practical implications: they are modeling a future Earth that we may be able to observe within the next 20 years.”