What Happens to Earth When All Humans Vanish

One December morning in 2032, NASA’s Jet Propulsion Laboratory calls an emergency conference of global astronomers. Near-Earth asteroid 2024 YR4 – discovered in early 2024 and initially assessed with a 1.6% impact probability – has become a critical concern.

New Webb Space Telescope data and updated tracking analysis from the International Asteroid Warning Network (IAWN) confirm the alarming trajectory: the 70-metre wide city-killer asteroid now shows a significantly increased chance of Earth impact.

With just 36 hours until potential impact, humanity faces a scenario long theorised by planetary defense experts. Despite years of planetary defence planning, the short notice and the asteroid’s size make intervention impossible. As governments worldwide scramble to respond, nature is about to conduct its grandest experiment since the disappearance of the dinosaurs.

While an asteroid impact isn’t the only scenario that could lead to humanity’s sudden absence – a highly infectious disease with extreme mortality rates could spread rapidly through our interconnected world – the outcome remains the same: a planet abruptly freed from human influence.

From the immediate aftermath to millennia-long transformations, we explore how our world would evolve in humanity’s absence.

The First Hours: A World Goes Silent

In the hours following humanity’s disappearance, an eerie silence would descend upon Earth.

The constant background hum of human civilisation – cars, machinery, and urban noise – would cease almost instantly. The skies would begin to clear as the constant stream of vehicle emissions and industrial pollution halts abruptly.

Satellite images would show city lights blinking out across the globe like dying stars as power grids fail cascade by cascade.

This silence would soon be broken by the sound of failing infrastructure. Without human operators, cooling systems would begin to fail, and pressure vessels would build to dangerous levels.

The first explosions would likely occur at petrochemical facilities and refineries, sending plumes of toxic smoke into the newly clearing skies.

The First Weeks: Infrastructure in Crisis

The most critical phase would occur within the first few weeks, as complex systems dependent on human maintenance begin to fail catastrophically.

The world’s 440 nuclear power plants pose the most immediate threat – their backup generators would run for days or weeks before failing, leading to multiple meltdowns across the globe. While devastating locally, these events wouldn’t spell the end for global life.

The Chernobyl Exclusion Zone has demonstrated nature’s resilience, with species like the Przewalski’s horse and European bison now thriving in areas abandoned by humans.

In coastal cities, the situation would become dire quickly. Modern metropolises like Tokyo, New York, and Sydney rely on constant pumping to keep their underground infrastructure dry. Within 36 hours, subway tunnels and underground carparks would begin to flood. The weight of this water, combined with natural erosion, would eventually lead to spectacular collapses of streets and buildings above.

The First Years: Nature’s Renaissance

As human-maintained spaces begin to deteriorate, nature would waste no time in reclaiming territory. The process would begin small but accelerate rapidly.

• Hardy pioneer species like moss and lichen would colonise our roads and highways
• Native grasses would push through cracks in pavements, their root systems gradually widening these fissures
• In temperate regions, fast-growing species like blackberries and ivy would begin to engulf abandoned structures
• Australian natives like wattles and eucalypts would rapidly colonise disturbed urban areas in their native range

The fate of domestic animals would vary dramatically by species and location. Most pets would suffer and die without human care, but some would adapt remarkably well.

Dogs might form feral packs, particularly successful in areas with abundant small prey. Cats, already responsible for devastating native wildlife populations, would likely thrive even more, returning to their natural predatory behaviours. In Australia, this could further impact native marsupial populations, though without human support, cat numbers would eventually stabilise.

Decades of Recovery: A New Balance Emerges

Over decades, the planet would begin to heal from human impact. The immediate cessation of greenhouse gas emissions would lead to gradually improving atmospheric conditions, though the effects of accumulated CO₂ would persist for centuries.

The regrowth of forests and grasslands would accelerate carbon sequestration, with an estimated 2.5 gigatonnes of carbon absorbed annually by recovering ecosystems.

Wildlife populations would explode in the absence of human pressure. Species currently threatened by habitat loss and hunting would rebound dramatically. In Australia, for instance, bilbies and numbats might reclaim their former ranges, while mainland zoo escapee Tasmanian devils could potentially re-establish mainland populations.

Centuries Later: A Transformed Earth

Several centuries post-human, Earth would be dramatically different. Most human structures would have collapsed, with cities reduced to overgrown ruins.

The Sydney Harbour Bridge might stand for a few centuries, but eventually, even this icon would succumb to corrosion and structural fatigue. The Sydney Opera House’s unique shell structure might persist longer, its ceramic tiles protecting the concrete beneath, but it too would eventually join the ruins of human civilisation.

Just as the jungle devoured Tikal’s pyramids in Guatemala and El Mirador’s massive temples in Petén, and the ancient city of Babylon crumbled beneath the Iraqi desert near modern-day Hillah, our greatest monuments would succumb to nature’s patient assault.

Like those ancient wonders, our skyscrapers and stadiums would become overgrown remnants, mysterious relics to any future intelligence that might discover them.

The concrete canyons of our cities would mirror the fate of Cambodia’s Angkor Wat and the surrounding metropolis of Angkor Thom – once-mighty structures surrendering to the inexorable march of strangler figs and weather, their original grandeur masked by vegetation and decay.

The process has already begun in places like Detroit’s Michigan Central Station and Hashima Island off Nagasaki, where abandoned human structures provide a preview of our cities’ fate.

The Great Barrier Reef, freed from the pressures of ocean acidification and warming, would begin a slow recovery. However, the legacy of coral bleaching events would have permanently altered its composition, with more heat-tolerant species dominating the new reef ecosystems.

The Millennial Perspective: Earth’s Memory of Humanity

Thousands of years into the future, Earth would retain subtle but telling traces of human existence. Future geology would reveal the distinct markers of the Anthropocene era:

• Layers of microplastics in sedimentary deposits
• A distinctive radiation signature from nuclear testing and accidents
• A sudden extinction event in the fossil record, followed by rapid speciation
• The remains of our cities, compressed into thin, artificial rock layers
• Unique mineral formations from our mining and manufacturing activities

The Planet’s Resilience

The Earth’s response to human disappearance would demonstrate both the profound impact of our species and the remarkable resilience of nature. While some of our legacy would persist for millennia, the planet would gradually heal and transform, finding new equilibriums and supporting flourishing life in our absence.

This thought experiment serves not only as a fascinating exploration of Earth’s natural processes but also as a stark reminder of humanity’s significant influence on our planet. It underscores the importance of understanding and managing our impact on Earth’s systems while we remain its stewards.

The timeline of recovery – potentially taking 3 to 7 million years to return to pre-human levels of biodiversity – highlights both the extent of our influence and the extraordinary resilience of life on Earth.