Without maintenance and fuel, most power plants (such as nuclear plants and wind turbines) would stop producing power. Consequently, most of the world would go dark.
Within days after human extinction, many pets and farm animals would die out due to starvation and dehydration.
All parasites that thrive on human existence, such as head lice and body lice, would go extinct.
Without power, electrical fences that used to keep livestock under control would stop working, releasing 1.5 billion cows, 1 billion pigs, and 20 billion chickens into the wild.
Pumps would stop working in subterranean tunnels and subway systems, which would result in massive floods.
After their cooling systems stopped working, some nuclear plants would explode.
Animal pests that live in human houses such as mice, rats, and cockroaches would suffer drastic declines and possibly also extinction.
Domesticated horses would possibly revert back to their original wild lifestyles.
Without maintenance, metal structures would begin to collapse due to corrosion.
The emission of industrial pollutants would cease, leading to a cleaner environment, eventually stopping global warming.
Small dog breeds whose survival instincts and features have been purposely bred out by humans would be killed off by larger and stronger creatures.
Within just 25 years after human disappearance, most of the planet’s paved city streets and sidewalks would be covered in vegetation.
Without firefighters, many structures all over the world would burn down in a fire.
Cities built in the desert such as Las Vegas or Dubai would be covered in sand in just a few years.
Most endangered animal and plant species would make a full recovery with no humans to harm them.
Approximately one year after human extinction, satellites around Earth would start to fall from their orbit, creating strange 'stars' in the sky.
Without power, raw sewage would slowly back up and begin to flood, polluting surrounding lakes and rivers.
Green places such as Central Park in New York would expand and take over entire cities.
Without maintenance, dams would crumble, creating devastating floods. Then, the flooded areas would probably turn into swamps.
After some time, houses made of wood would be completely eaten away by termites.
Humans have managed to crossbreed and perfect fruits and vegetables to make them more plentiful, palatable, and easier to grow, but in just 2 decades without human cultivation, vegetation would revert back to its original strains and wild forms.
Several hundred years after humans disappeared, wildlife would be abundant in every part of world. However, there possibly would be a redistribution of the species as some escaped Zoo animals might form new wild populations in places where they never lived naturally before.
Within 100,000 years, C02 levels in the atmosphere would finally return to the levels they were before humans walked the Earth.
The oceans would be soon full of fish and marine wildlife, almost equal to what it was before humans started to exploit it.
The only evidence of our existence some 10,000 years after our disappearance would be things made with stone like the pyramids in Egypt, the Great Wall of China, and Mount Rushmore. Everything else would be gone.