Earth will retain its oxygen-rich atmosphere for another one billion years before experiencing rapid deoxygenation, according to computer models created by researchers at Toho University and the Georgia Institute of Technology. The study highlights that oxygen-rich conditions may account for as little as 20–30% of Earth’s history.
Earth’s breathable atmosphere is not a permanent fixture of the planet, and scientific modeling shows it has a definitive expiration date. While long-term discussions about the biosphere’s future have historically focused on the steady brightening of the Sun and the global carbonate-silicate geochemical cycle, researchers have now simulated the eventual collapse of atmospheric oxygen using advanced computer models. For many years, the lifespan of Earth's biosphere has been discussed based on scientific knowledge about the steady brightening of the Sun and global carbonate-silicate geochemical cycle,
says Ozaki.
Computer Models Simulate the 1-Billion-Year Countdown at Toho University and Georgia Institute of Technology
To examine how Earth’s atmosphere will evolve, Kazumi Ozaki, Assistant Professor at Toho University and Christopher Reinhard, Associate Professor at Georgia Institute of Technology, created a model of Earth on a computer to simulate climate and biochemical processes. The study, published in Nature Geoscience, found the future lifespan of Earth’s oxygen-rich atmosphere is 1 billion years.
Kazumi Ozaki, Toho University
The modeling demonstrates that a continuous decline in atmospheric carbon dioxide levels will eventually starve photosynthetic organisms of the gas they need to survive. As the Sun continues to brighten, overheating combined with carbon dioxide scarcity will trigger the collapse of the terrestrial biosphere. Long before that final thermal tipping point, however, atmospheric oxygen levels will drop precipitously.
Rapid Deoxygenation Will Return Earth to an Anaerobic World
When the one-billion-year window closes, Earth will undergo rapid deoxygenation that strips away the ozone layer and leaves behind an atmosphere characterized by elevated methane levels and low carbon dioxide. The transition will effectively reset the planet’s atmospheric chemistry to a state similar to the period before the Great Oxidation Event. This happened around 2.5 billion years ago and, while the exact cause is debated, it’s thought that single-celled organisms are largely responsible for the Great Oxidation Event. Whatever the cause, this was a key epoch in the evolution of Earth, producing breathable oxygen that would make our planet habitable for a variety of larger organisms.
The atmosphere after the great deoxygenation is characterised by an elevated methane, low-levels of CO2, and no ozone layer.
Kazumi Ozaki, Toho University
Astronomers routinely hunt for atmospheric oxygen as a primary biosignature when observing exoplanets orbiting distant stars. The Toho University and Georgia Institute of Technology findings indicate that an oxygenated atmosphere is a transient phase rather than an enduring planetary characteristic, likely spanning as little as 20 to 30 percent of Earth’s history.
Aquatic Deoxygenation Threatens Modern Oceans Across Freshwater and Marine Ecosystems
While the atmospheric collapse remains far in the future, a separate line of research warns that contemporary aquatic systems are already losing oxygen at an alarming rate. Scientists led by UC San Diego’s Scripps Institution of Oceanography are warning that oxygen is disappearing rapidly from oceans and freshwater systems, potentially pushing the planet into an “unsafe space.” Some of the resulting changes could persist for centuries and may not be reversible within human lifetimes. The new review examines aquatic deoxygenation, which refers to declining levels of dissolved oxygen in the ocean (ocean deoxygenation), coastal waters, rivers, lakes and streams. The researchers assessed how this growing problem interacts with the nine major Earth system processes included in the Planetary Boundaries framework. Introduced in 2009, the framework identifies environmental processes that are essential for maintaining a stable and resilient planet. It also tracks how human activity is pushing those systems beyond safe conditions. The nine planetary boundaries are climate change, ocean acidification, biodiversity loss, atmospheric aerosol loading, stratospheric ozone depletion, freshwater change, land-use change, chemical pollution and biogeochemical flows (including the nitrogen cycle). The researchers argue that dissolved oxygen levels should also be formally included.
The health and stability of our planet depends on the health and stability of aquatic ecosystems, which need oxygen to function normally,
said lead author Erica Ferrer, a Scripps Oceanography alumna and current postdoctoral scholar at UC Santa Barbara’s National Center for Ecological Analysis and Synthesis. This study is designed to elevate the profile of aquatic deoxygenation as a global threat and show that it does not operate in isolation.
Erica Ferrer, postdoctoral scholar at UC Santa Barbara’s National Center for Ecological Analysis and Synthesis
Human-caused warming, excessive nutrient pollution and changes in the movement and ventilation of deeper waters are the main forces driving aquatic deoxygenation. As oxygen levels fall, they can disrupt the biological and chemical processes that help regulate Earth’s climate. The decline also threatens organisms across aquatic food webs, from microscopic life to fish and sharks. Marine mammals can also suffer even though they breathe air at the surface. Oxygen loss can reduce or relocate their prey, damage habitats and alter the food webs they depend on. Ferrer and Scripps biological oceanographer Lisa Levin, the study’s senior author, developed the idea for the review after attending COP25, the 2019 United Nations Climate Change Conference held in Madrid. They hope the findings will encourage researchers and policymakers to examine aquatic oxygen loss alongside climate change, pollution, and other pressures on the planet.