In one billion years, Earth will be a dramatically different planet. The sun will be roughly 10% brighter than it is today, pushing surface temperatures high enough to trigger a slow but irreversible loss of the oceans. Most complex life will be gone. The planet won’t be destroyed, but it will become hostile to nearly everything living on it now.
The Sun Gets Brighter Over Time
The sun is not a static object. It grows steadily more luminous as it ages, burning through hydrogen fuel in its core and gradually expanding its energy output. This isn’t a sudden event or a dramatic explosion. It’s a slow, relentless increase that has been happening since the sun formed 4.6 billion years ago and will continue for billions more.
By one billion years from now, solar luminosity will have increased by approximately 10%. That sounds modest, but the effects on Earth’s climate are enormous. According to NASA calculations, when the sun reaches 20% brighter (roughly two billion years out), the change is already well past what Earth’s climate systems can absorb. At the one-billion-year mark, we’re firmly on that trajectory, with global temperatures climbing far beyond anything in human experience.
For context, the difference between today’s climate and an ice age involves a global temperature shift of only about 5 to 6 degrees Celsius. A 10% increase in solar output pushes temperatures well beyond that range, fundamentally altering the water cycle, atmospheric chemistry, and the conditions that support life.
How Earth Loses Its Oceans
The most consequential change in one billion years is the beginning of the end for Earth’s oceans. As the sun brightens, more water evaporates into the atmosphere. Water vapor is itself a powerful greenhouse gas, so more evaporation leads to more warming, which leads to more evaporation. This feedback loop is called a “moist greenhouse” state.
In a moist greenhouse, water vapor reaches high into the upper atmosphere, where ultraviolet radiation from the sun splits water molecules apart. The hydrogen atoms, light enough to escape Earth’s gravity, drift off into space permanently. Over hundreds of millions of years, this process strips the planet of its water, molecule by molecule. This is exactly what happened to Venus early in its history: rapid splitting of water vapor followed by hydrogen escaping to space, leaving the planet bone-dry.
Research on runaway greenhouse thresholds suggests the critical point where water loss accelerates dramatically could occur when solar energy reaching Earth is as little as 1.1 times its current level. A full runaway greenhouse, where oceans evaporate entirely, is estimated to require about 1.4 times current solar output. One billion years from now, Earth will likely be somewhere in the early stages of this process. The oceans won’t vanish overnight, but they’ll be shrinking steadily, and the atmosphere will be thick with water vapor and increasingly inhospitable.
What Happens to Life
Complex life, including plants, animals, and fungi, will almost certainly be gone well before the billion-year mark. Rising temperatures and shifting atmospheric composition will collapse ecosystems long before the oceans fully evaporate. Plants depend on a specific range of carbon dioxide and temperature to photosynthesize, and models suggest that window closes within the next 500 to 800 million years. Without plants, the oxygen-dependent food chains that support animals collapse in turn.
Microbes are another story. Extremophile organisms, microbes that thrive in conditions lethal to everything else, have actually dominated Earth’s biological history. Life existed for billions of years before complex organisms appeared, and it will likely persist long after they’re gone. The theoretical boundaries for life span from negative 40°C to roughly 150°C, above which the molecular machinery of even the hardiest cells falls apart. As long as temperatures somewhere on Earth stay within that range, microbial life has a chance.
The surface may become uninhabitable, but Earth’s subsurface is a different environment. Underground rock formations warmed by geothermal heat, shielded from solar radiation, and supplied with chemical energy from water-rock interactions could shelter microbial communities for a very long time. A process called serpentinization, where water reacts with iron-rich minerals deep underground, produces hydrogen gas and simple organic compounds that certain microbes can feed on. These chemoautotrophic organisms don’t need sunlight or oxygen. They live on chemistry alone, and they could represent the last holdouts of life on a dying Earth.
Researchers have noted that extremophiles, particularly those adapted to multiple harsh conditions simultaneously, may actually be the most abundant life forms on the planet even today. Most of Earth’s microbial biomass lives underground, not on the surface. In a billion years, that underground biosphere may be all that’s left.
The Planet Itself
Earth’s geology will also be winding down. Plate tectonics, the engine that recycles the crust, builds mountains, and drives volcanic activity, depends on internal heat from radioactive decay. That heat is slowly dissipating. In one billion years, tectonic activity will be weaker, though not yet stopped entirely. Volcanic eruptions will be less frequent, which matters because volcanoes are a major mechanism for recycling carbon dioxide back into the atmosphere. With less volcanism and more solar heat, Earth’s carbon cycle breaks down further.
The planet’s magnetic field, generated by convection in the liquid iron core, will also be weakening as the core slowly cools. A weaker magnetic field means less protection from solar wind, which accelerates the stripping of atmospheric gases. Mars lost most of its atmosphere through this process after its magnetic field died billions of years ago. Earth in one billion years won’t be as far gone as Mars, but it will be trending in that direction.
What Earth Might Look Like
Picture a planet that resembles a hotter, wetter version of early Venus. Surface temperatures likely exceed 70°C (around 160°F) or higher in many regions. The oceans are smaller and shallower, evaporating faster than they can be replenished. The atmosphere is dense with water vapor and carbon dioxide. The sky may appear hazy or white rather than blue. No forests, no grasslands, no visible animal life. The continents, no longer sculpted by the same intensity of tectonic forces, are flatter and more eroded.
Deep underground, in cracks and pores in the rock where temperatures are still manageable, colonies of heat-loving microbes carry on. They feed on hydrogen and simple chemicals seeping from mineral reactions, completely unaware of the transformation happening above them. They are the descendants of organisms that have been living this way for billions of years already. In one billion years, they’ll be Earth’s last biosphere, persisting in darkness until even the deep rock grows too hot to sustain the molecular structures that make life possible.