Suppose all the humans disappeared from the Earth leaving everything else (including all the flora and fauna) intact.  What would the world be like?  Alan Weisman's book The World Without Us tries to answer this hypothetical question.  By thinking about this question, we begin to realize our human impact on this world and its ecosystem.

This book is not a work of fiction.  It is written in the style of journalistic reporting with interviews of people in the relevant area of expertise.  In fact, Time magazine and Entertainment Weekly both named it the #1 non-fiction book of 2007.  It was a New York Times bestseller as well as finalist for the 2007 National Book Critics Circle Award.

Well to begin with... If humans were not around to maintain our infrastructures, nature's water will be the first element that will start tearing our structures apart.  It would rust our nails and seep into our buildings via leaks and chimney flashings.  With water available, weeds and wild flora will florish until you have trees growing through houses, weeds breaking up sidewalks, and with enough time even a city like New York city will crumble. 

Without people fixing bursting pipes and maintaining the pumps that keeps water out of the New York subway system, the subway would flood and ceiling would cave in.  Streets will buckle and crack with the constant freeze thaw cycle of the seasons.  Petroleum tanks will explode as corrosion eats away at it.

We can already see the effects of nature overtaking our environment in places that had been adbandoned by humans due to political reasons.  Due to war, a hotel in Varosha, Cyprus was completely abandoned in 1974.  Just two years later, pavements have cracked with weeds coming three feet high in the middle of streets.  30 years later, nothing is savagable.  Nature had claimed it with geraniums growing from roofs, lizards and snakes roaming about six-foot tall grass. 

Korea's demilitarized zone (DMZ) that resulted from World War II have been without people since 1953.  Now animals such as black bears, lynx, deer, and goats take refuse there.

Another place without people is the 30-kilometer-radius known as "The Zone of Alienation" where the Chernobyl nuclear power plant explosion happened, releasing nuclear fallout such as cesium-137 and strontium-90 that have 30-year half-lives.

While many man-made structure will disappear, other man-made elements will remain for a long long time.  Even if humans were able to shut down all the nuclear reactors before they disappeared, the uranium fuel is still hot and still generates 7% of the normal heat of an active reactor.  Without humans keeping the machinery running to keep this cool, surely one of the 441 nuclear plants on the planet would overheated.

The uranium fuel itself would continue to decay.  It would take 704 millions years before just half of it decays away.  Similarly, the spent fuel of the nuclear reactors would also be around for a long time.

Plastics is another substance that will be present long after we are gone. It biodegrades at such slow rates that it is hardly significant.  Three million tons of it has already ended up in the oceans at Great Pacific Garbage Patch. Those plastic that ends up at the bottom of oceans can take 100,000 years to disappear.

Without cars and factories emitting heavy metals into the atmosphere, each season's rainfall will contain fewer and fewer contaminants.  Plants naturally will take up some of these contaminants, die, and get buried into the ground.  Hence newer crops of plants that take their place will flourish more and more. 

Nevertheless, zinc in our soils may last 3,700 years.  Cadmium may last 7,500 years.  Lead, 35,000 years.  And chromium 70,000 years.  Even trace plutonium have been detected in our soils starting in early 1950.  This is known from the Rothamsted Research Archives which contains 300,000 soil samples.

Chapter 12 of the book is titled "The Fate of Acient and Modern Wonders of the World".  Weisman briefly describes and then speculates on what would happen to The Chunnel, the Panama Canal, Egypt's Khufu pyramid, and Great Wall of China.

In any case, we need not speculate any further than 5 billion years from now.  Because that is when the Sun will expand into a red giant star and gobble up the inner planets with Earth included.
 

Article written in 2009. Author may receive Amazon and Google revenues via display ads and links in this article.