The biological and geological future of Earth can be extrapolated based on the estimated effects of several long-term influences. These include the chemistry at Earth's surface, the cooling rate of the planet's interior, gravitational interactions with other objects in the Solar System, and a steady increase in the Sun's luminosity. An uncertain factor is the influence of human technology such as climate engineering, which could cause significant changes to the planet. For example, the current Holocene extinction is being caused by technology, and the effects may last for up to five million years. In turn, technology may result in the extinction of humanity, leaving the planet to gradually return to a slower evolutionary pace resulting solely from long-term natural processes.
Over time intervals of hundreds of millions of years, random celestial events pose a global risk to the biosphere, which can result in mass extinctions. These include impacts by comets or asteroids and the possibility of a near-Earth supernova—a massive stellar explosion within a radius of the Sun. Other large-scale geological events are more predictable. Milankovitch's theory predicts that the planet will continue to undergo glacial periods at least until the Quaternary glaciation comes to an end. These periods are caused by the variations in eccentricity, axial tilt, and precession of Earth's rotation and orbit. As part of the ongoing supercontinent cycle, plate tectonics will probably create a supercontinent in 250–350 million years. Sometime in the next 1.5–4.5 billion years, Earth's axial tilt may begin to undergo chaotic variations, with changes in the axial tilt of up to 90°.
The luminosity of the Sun will steadily increase, causing a rise in the solar radiation reaching Earth and resulting in a higher rate of weathering of silicate minerals. This will affect the carbonate–silicate cycle, which will reduce the level of carbon dioxide in the atmosphere. About 600 million years from now, the level of carbon dioxide will fall below the level needed to sustain C3 carbon fixation photosynthesis used by trees. Some plants use the C4 carbon fixation method to persist at carbon dioxide concentrations as low as ten parts per million. However, in the long term, plants will likely die off altogether. The extinction of plants would cause the demise of almost all animal life since plants are the base of much of the animal food chain.
In about one billion years, solar luminosity will be 10% higher, causing the atmosphere to become a "moist greenhouse", resulting in a runaway evaporation of the oceans. As a likely consequence, plate tectonics and the entire carbon cycle will end. Then, in about 2–3 billion years, the planet's magnetic dynamo may cease, causing the magnetosphere to decay, leading to an accelerated loss of volatiles from the outer atmosphere. Four billion years from now, the increase in Earth's surface temperature will cause a runaway greenhouse effect, creating conditions more extreme than present-day Venus and heating Earth's surface enough to melt it. By that point, all life on Earth will be extinct. Finally, the planet will possibly be engulfed by the Sun in about 7.6 billion years, after the star has entered the red giant phase and expanded beyond the planet's current orbit. However, a newer study in 2026 suggests that it is likely that the Earth will survive engulfment.
Human influence
Humans play a key role in the biosphere, with the large human population dominating many of Earth's ecosystems. This has resulted in a widespread, ongoing mass extinction of other species during the present geological epoch, now known as the Holocene extinction. The large-scale loss of species caused by human influence since the 1950s has been called a biotic crisis, with an estimated 10% of the total species lost as of 2007. At current rates, about 30% of species are at risk of extinction in the next hundred years. The Holocene extinction event is the result of habitat destruction, the widespread distribution of invasive species, poaching, and climate change. In the present day, human activity has had a significant impact on the surface of the planet. More than a third of the land surface has been modified by human actions, and humans use about 20% of global primary production. The concentration of carbon dioxide in the atmosphere has increased by close to 50% since the start of the Industrial Revolution.
The consequences of a persistent biotic crisis have been predicted to last for at least five million years. It could result in a decline in biodiversity and homogenization of biotas, accompanied by a proliferation of species that are opportunistic, such as pests and weeds. Novel species may emerge; in particular taxa that prosper in human-dominated ecosystems may rapidly diversify into many new species. Microbes are likely to benefit from the increase in nutrient-enriched environmental niches. No new species of existing large vertebrates are likely to arise and food chains will probably be shortened.
There are multiple scenarios for known risks that can have a global impact on the planet. From the perspective of humanity, these can be subdivided into survivable risks and terminal risks. Risks that humans pose to themselves include climate change, the misuse of nanotechnology, a nuclear holocaust, warfare with a programmed superintelligence, a genetically engineered disease, or a disaster caused by a physics experiment. Similarly, several natural events may pose a doomsday threat, including a highly virulent disease, the impact of an asteroid or comet, runaway greenhouse effect, and resource depletion. There may be the possibility of an infestation by an extraterrestrial lifeform. The actual odds of these scenarios occurring are difficult if not impossible to deduce.
Should the human species become extinct, then the various features assembled by humanity will begin to decay. The largest structures have an estimated decay half-life of about 1,000 years. The last surviving structures would most likely be open-pit mines, large landfills, major highways, wide canal cuts, and earth-fill flank dams. A few massive stone monuments like the pyramids at the Giza Necropolis or the sculptures at Mount Rushmore may still survive in some form after a million years.
Cataclysmic astronomical events
As the Sun orbits the Milky Way, wandering stars such as Gliese 710 may approach close enough to have a disruptive influence on the Solar System. A close stellar encounter could cause a significant reduction in the perihelion distances of comets in the Oort cloud—a hypothetical spherical region of icy bodies orbiting within half a light-year of the Sun. Such an encounter could trigger a 40-fold increase in the number of comets reaching the inner Solar System. Impacts from these comets could trigger a mass extinction of life on Earth. These disruptive encounters are estimated to occur an average of once every 45 million years. There is a 1% chance every billion years that a star will pass within of the Sun, potentially disrupting the Solar System. The mean time for the Sun to collide with another star in the solar neighborhood is approximately 30 trillion () years, which is much longer than the estimated age of the Universe, at approximately 13.8 billion years. This can be taken as an indication of the low likelihood of such an event occurring during the lifetime of the Earth. Based on results from the Gaia telescope's second data release from April 2018, an estimated 694 stars will approach the Solar System to less than 5 parsecs in the next 15 million years. Of these, 26 have a good probability to come within and 7 within .
The energy released from the impact of an asteroid or comet with a diameter of or larger is sufficient to create a global environmental disaster and cause a statistically significant increase in the number of species extinctions. Among the deleterious effects resulting from a major impact event is a cloud of fine dust ejecta blanketing the planet, blocking some direct sunlight from reaching the Earth's surface thus lowering land temperatures by about within a week and halting photosynthesis for several months (similar to a nuclear winter). The mean time between major impacts is estimated to be at least 100 million years. During the last 540 million years, simulations demonstrated that such an impact rate is sufficient to cause five or six mass extinctions and 20 to 30 lower severity events. This matches the geologic record of significant extinctions during the Phanerozoic Eon. Such events can be expected to continue.
A supernova is a cataclysmic explosion of a star. Within the Milky Way galaxy, supernova explosions occur on average once every 40 years. During the history of Earth, multiple such events have likely occurred within a distance of 100 light-years; known as a near-Earth supernova. Explosions inside this distance can contaminate the planet with radioisotopes and possibly impact the biosphere. Gamma rays emitted by a supernova react with nitrogen in the atmosphere, producing nitrous oxides. These molecules cause a depletion of the ozone layer that protects the surface from ultraviolet (UV) radiation from the Sun. An increase in UV-B radiation of only 10–30% is sufficient to cause a significant impact on life; particularly to the phytoplankton that form the base of the oceanic food chain. A supernova explosion at a distance of 26 light-years will reduce the ozone column density by half. On average, a supernova explosion occurs within 32 light-years once every few hundred million years, resulting in a depletion of the ozone layer lasting several centuries. Over the next two billion years, it is predicted that there will be about 20 supernova explosions and one gamma ray burst that will have a significant impact on the planet's biosphere.
The incremental effect of gravitational perturbations between the planets causes the inner Solar System as a whole to behave chaotically over long time periods. This does not significantly affect the stability of the Solar System over intervals of a few million years or less, but over billions of years, the orbits of the planets become unpredictable. Computer simulations of the Solar System's evolution over the next five billion years suggest that there is a small (less than 1%) chance that a collision could occur between Earth and either Mercury, Venus, or Mars. During the same interval, the odds that Earth will be scattered out of the Solar System by a passing star are on the order of 1 in 100,000 (0.001%). In such a scenario, the oceans would freeze solid within several million years, leaving only a few pockets of liquid water about underground. There is a remote chance that Earth will instead be captured by a passing binary star system, allowing the planet's biosphere to remain intact. The odds of this happening are about 1 in 3 million.
Orbit and rotation The gravitational perturbations of the other planets in the Solar System combine to modify the orbit of Earth and the orientation of its rotation axis. These changes can influence the planetary climate. Despite such interactions, highly accurate simulations show that overall, Earth's orbit is likely to remain dynamically stable for billions of years into the future. In all 1,600 simulations, the planet's semimajor axis, eccentricity, and inclination remained nearly constant.
Glaciation