I am in Scotland with Jan Zalasiewicz, a British stratigrapher. His job is to study rock layers.
He shows me a rock. It has a dark marking on it that is about 1 meter (three feet) thick. He tells me this shows a major event that happened over 400 million years ago. The marking tells him that four out of every five sea animals were killed in the event.
Stratigraphers like Zalasiewicz are often hard to impress. Their job is to learn Earth's history by finding clues in rocks that are millions of years old. Only the most violent events are likely to leave behind clear, lasting signals of what happened. These events mark the most important chapters in the planet's 4.5-billion-year story.
So, it's scary to learn what many stratigraphers now believe. They think human beings have changed the planet so much in the past 100 or 200 years that we've begun a whole new epoch. This epoch is called the Anthropocene.
Geologists, who study rocks, divide Earth's history into epochs. Epochs can be tens of millions of years long. Periods, such as the Cretaceous, when dinosaurs roamed, lasted much longer. Eras, like the Mesozoic, longer still.
I ask Zalasiewicz what he thinks our current epoch will look like to future geologists. Will it show up as a sharp band in which very bad things happened, like a mass extinction? We're still trying to figure that out, Zalasiewicz says.
New Word Comes To Life
The word Anthropocene was invented by Dutch chemist Paul Crutzen about 10 years ago. He wrote a paper that used the term. It quickly became popular among many scientists.
Human effects on the world have become more and more obvious. There are nearly seven billion people in the world. Scientist E. O. Wilson calculated that the weight of all humans on Earth is already a hundred times larger than that of any other large animal species.
In 2007, Zalasiewicz decided to ask other stratigraphers what they thought of the Anthropocene. Twenty-one of 22 thought the concept made sense. They asked themselves if the Anthropocene could count as a real epoch. This depends on a few factors.
Usually, epochs are based on what geologists find in different sediments. These sediments are rocks and earth that have accumulated at the bottom of oceans and rivers. Geologists study these rocks and look for fossils of ancient creatures. Each epoch has its own types of fossils.
Of course, no fossils exist from the present. But when they form, will they show the effects of human actions? Will our actions leave a mark, like those large wide bands in rocks from the past? The answer, Zalasiewicz's group decided, is yes.
First, though, it is important to know what won't show up on the rocks.
Surprisingly, cities will not leave much of a trace. Since they are built on land, even the strongest steel and concrete will be washed away by erosion. The process of erosion occurs when wind, rain and other forces wear away at a material.
Farming Will Leave No Major Imprint
Humans have also transformed the world through farming. Around two-fifths of the planet's ice-free land is now used for agriculture. Even in this case, the effects won't be that noticeable in the long run. Future scientists might notice the types of plants we used most. They may find large amounts of pollen from corn, wheat and soy, for example.
However, one of the most noticeable effects will come from the forests we destroy. Fewer trees mean that more soil will erode, or wear off. More erosion means more sediment will dump into rivers and seas.
On top of this, many creatures live in trees. They are losing their homes as more trees get cut down. This is leading to the extinction of many species. The number of species going extinct today is thousands of times higher than in the past 500 million years.
Yet, the biggest effect has to do with the air. When we burn fuels like gas and wood, carbon dioxide is released in the air. Carbon dioxide is a greenhouse gas. That's because it traps heat in the air, causing temperatures to rise. Carbon's warming effects could easily push global temperatures to levels that have not been seen for millions of years.
Some plants and animals are already moving toward the North and South Poles. The reason is those areas are getting warmer and more livable for animals that wouldn't normally be there. Some species will not survive global warming at all. Meanwhile, rising temperatures could raise sea levels six meters (20 feet) or more.
Long after our cities have turned to dust, the effects of burning billions of tons' worth of coal and oil should be obvious. As carbon dioxide warms the planet, it also seeps into the oceans. This makes them more acidic, which is bad for coral reefs. There could be a point in this century that corals can no longer make reefs. Geologists would call this a reef gap.
Asteroid Likely Caused Last Major Mass Extinction
Reef gaps have happened with each of the past five major mass extinctions on Earth. The most recent one is believed to have been caused when an asteroid hit the planet. It took place 65 million years ago. It killed all dinosaurs and many other creatures. The scale of what's happening to the oceans today is probably around the same level of importance. To future geologists, Zalasiewicz says, our impact may look as sudden and powerful as that of an asteroid.
If we have started a new epoch, when exactly did it begin?
William Ruddiman studies climate history at the University of Virginia. He said that the invention of farming 8,000 years ago and deforestation led to a higher level of carbon dioxide in the air. It was just high enough to hold off what otherwise would have been a new ice age.
Crutzen has suggested that the Anthropocene began in the late 1700s. This is shown by ice cores, or long samples of ice that accumulated over a long time. These ice cores show that, about 300 years ago, carbon dioxide levels began to rise.
Other scientists say the new epoch began in the middle of the 1900s. That was the time when industry and the population started to grow much faster than before.
The International Commission on Stratigraphy (ICS) is a large science organization. It will officially decide whether this epoch should be called the Anthropocene. The decision is likely to take years. If we wait, maybe the effects of humans may be clearer.
Crutzen does not really care if the word Anthropocene gets added to textbooks. What he wants is to focus attention on our actions as humans, and on how we might still stop the worst. "What I hope," he says, "is that the term 'Anthropocene' will be a warning to the world."