The millions upon millions of gallons of oil hemorrhaging into the Gulf of Mexico every day is a crude reminder of the many ways humans are fouling the planet. As forests are cleared, cities and suburbs paved and expanded, as the air and sea warm and become increasingly polluted with cancer-causing chemicals and garbage, and with species dropping like flies, the planet's health is being challenged in ways that have not occurred in its entire 4.5-billion-year existence.
Can Earth survive?
The simple answer is a resounding "yes."
When humans are gone, as the fossil record suggests will happen eventually, Earth will clean itself up and take on yet another new look, just as it has done many times in the past. In many ways, Earth's existence has been tested far more dramatically in the past than by anything humans have thrown at it. From its origins as a giant lava ball to an epoch that engulfed the entire planet in ice a mile deep, this planet has seen it all. Our planet was even purple for awhile, scientists say.
"As far as the solid Earth, I doubt if it cares much about life on Earth," said Richard Carlson, a geochemist at the Carnegie Institution of Washington in D.C. "So volcanoes, plate tectonics, earthquakes, etc. likely would go on as before."
The Earth may care little, but humans certainly have reason to figure out how to better survive the planet's changes, whether natural or caused by people.
Some like it hot
Earth is thought to have formed from protoplanetary bodies colliding during the chaotic early days of the solar system. Barely 30 million to 50 million years later, a catastrophic smashup took place between the youngplanet and a smaller Mars-sized object, reshaping the world dramatically around 4.5 billion years ago.
That early violence helped spawn the moon. More giant impacts between 4.1 billion and 3.9 billion years ago may have shaped the continents and possibly even re-melted the solidifying planetary crust, scientists say.
More recently, supervolcanoes that dwarf anything seen in recorded history wreaked additional havoc. One series of eruptions around 65 million years ago spewed lava across an area more than twice the size of Texas.
But the world has not ended in fire just yet, and it even survived a "snowball Earth" period between 710 million and 640 million years ago that put ordinary ice ages to shame. Geologists have found evidence that sea iceand glaciers reached all the way to the equator during that period.
Despite all the upheaval, life managed to not only survive but thrive. A thick organic haze of methane and nitrogen may have helped out by keeping the planet unfrozen early on,scientists suggest.
The rise of life on Earth may not have shaken things up in a geological sense, but it did give a makeover to the planet's chemistry. Now humans represent the latest to alter the balance of life and chemistry on the planet during our relatively short existence.
Turn and face the strain
Species are going extinct at a rate between 1,000 and 10,000 times higher than the expected natural extinction rate based on the fossil record, according to the International Union for the Conservation of Nature, which is charged with officially declaring endangered or extinct species.
Forests that once covered continents such as Europe now look like shadows of their former selves after hundreds of years of land clearing. Deforestation has begun to slow in the last decade, but an area of forest the size of Vermont and New Hampshire combined is still destroyed each year, said a recent report by the U.N. Food and Agriculture Organization.
All major fisheries have collapsed due to overfishing, and rising carbon dioxide levels raise the specter of moremass extinction among marine life due to ocean acidification - not unlike what has happened previously during the Earth's history.
Humans have even changed the atmosphere, as in the case of chlorofluorocarbons(CFCs) used as refrigerants. The ozone-destroying chemicals could have created a world where a permanent ozone layer hole yawned above Antarctica and people sunburned within minutes, if not for the Montreal Protocol that banned CFCs in 1989.
Such changes may have proved ruinous for humans, but Earth itself would have shrugged them off.
"If these [major chemical changes in the atmosphere] were big enough to kill off humanity, the atmosphere likely would recover pretty quickly, at least on geologic time scales," Carlson told LiveScience.
Similarly, the Earth has stoically endured climate changefar beyond anything experienced by humans. But history shows that human civilization remains vulnerable to even minorshifts in climate patterns.
For instance, a cooler Pacific Ocean has been connected with drier climate and drought conditions that led to famines in Medieval Europe, and perhaps the disappearance of cliff-dwelling natives of the American West.
Now global warming driven by greenhouse gases may lead to even wilder climate fluctuations in different parts of the world. Rates of increasing carbon dioxide areapproximately 100 times greater than most changes previously seen during geologic time, according to researchers on the Ocean Carbon & Biogeochemistry website.
Whether or not humans choose to deal with greenhouse gases, Earth's history shows that they inevitably face a running battle with climate change. Species that couldn't adapt in the past have died, and odds are that humanity's number will be up at some point.
The things we leave behind
"There will definitely be minute traces of us around, but I suspect most of the stuff that says we were here will be buried by geology," said Alan Weisman, a journalist and author of the book "The World Without Us" (Thomas Dunne Books, 2007).
Many of humanity's most visible achievements would vanish quickly. Buildings would crumble and decay within just 10,000 to 15,000 years. A bronze bust could survive for millions of years, Weisman said, even if it toppled and ended up buried, as would be likely.
Some more lasting effects on the Earth might come from the chemicals that would leak from their tanks within decades, or nanoparticles being engineered every day inside labs.
"We've created some chemical molecules that nothing in nature knows how to break down yet," Weisman pointed out. "Some, nature will figure out. Microbes will figure out how to do plastic."
A more deadly legacy for life after humans comes from more than 440 nuclear power plants. Overheating would cause about half to burn and the rest to suffer meltdowns, releasing radioactivity into the air and nearby water. Unattended refineries and chemical plants could also start burning and in turn releasing chemicals.
The equivalent of hundreds of Chernobyl disasters "would probably start forcing evolution in pretty dramatic ways," Weisman said.
Still, the Earth had already experienced nuclear fission almost 2 billion years ago. Several uranium deposits at Oklo in the Republic of Gabon, a southwestern region of Africa, showed evidence of having operated as natural nuclear reactors for several hundred thousand years.
Earth also has experience dealing with oil spills, given along history of natural oil seepage in places such as the Gulf of Mexico. Wild microbes that have evolved to break down oil no doubt found an unusually bountiful feast in recent months because of the Gulf oil gusher from the BP oil rig disaster.
That "horrifying" event may register as just a blip on the Earth's radar. But it still seems like a very long-term mess for the humans who have to live with it, Weisman noted.
"The oil sucks," Weisman said. "You can quote me on that."