Like the pages of a book, rocks tell stories. Each of its layers encapsulates stories that contain information about the molecules that existed in the atmosphere of past times, the temperature it was doing, the animals and plants that lived then and the habitats they occupied. Each chapter starts from scratch, with a complete change of environments, plot and characters. Abrupt beginnings and violent endings that allow defining the hierarchical series of divisions of geological time, a reflection of the main events in the history of the planet.
According to the International Commission of Stratigraphy (ICS, for its acronym in English), the body responsible for establishing these formal limits, the present is situated in the time known as the Holocene, which in turn is integrated into the quaternary period (initiated 2.5 million years ago), in the Cenozoic era (66 million years) and within the Phanerozoic eon (541 million years), which marks the beginning of the expansion of life.
The Pleistocene ushered in the second Quaternary epoch, the Holocene, which began 11,700 years ago and in which Homo sapiens developed agriculture, domesticated animals, created increasingly complex tools, built urban settlements and began to alter the environment through large scale . As a consequence, the footprint left by our species today is so deep that an increasing number of scientists believe that we have already entered a third Quaternary epoch: the Anthropocene.
“I used this word for the first time in 2000 during a conference,” recalls atmospheric chemist and Nobel Prize winner Paul Crutzen. And he adds: “We were talking about the alterations that the planet has suffered and someone mentioned the Holocene. But the world has changed so much that it didn’t seem right to keep talking about it. In the heat of the moment it occurred to me to say that we are in the Anthropocene, and the idea took hold ”.
Today, this neologism appears in hundreds of studies and in the name of three scientific journals . Jan Zalasiewicz, a geologist at the University of Leicester, recalls that “the Anthropocene began to appear in serious publications. It was unheard of in the world of geological scales. I found that most of my colleagues thought that the term was appropriate ”.
But is there really something new in the current chapter in Earth’s history? ” Episodes of global warming, ocean acidification or mass extinctions have occurred long before humans reached the planet, ” Zalasiewicz clarifies. Philip Gibbard, former head of the ICS international panel overseeing the Quaternary, realized that they needed to “study whether or not the formalization of the Anthropocene was justified.” Thus, in 2009 the Anthropocene Working Group (AWG) was formed, led by Zalasiewicz and whose purpose is, according to him, “to assess whether there is data that justifies adding a new unit of time to the geological scale.”
More powerful than the wind and waves
The issue is complex. “For more than two centuries, the geoscientific community has accepted the axiom that the present is the key to the geological past,” explains James Syvitski, member of the AWG and leader of the International Geosphere-Biosphere Program. “However, if the Anthropocene shows that the human footprint dominates the signal of many of the relevant geological phenomena – for example, that we move more sediments than glaciers, winds, waves and rivers combined – we are facing a revolutionary concept. Man as a geological force, capable of changing the planet ”.
To define a unit of geological time, its oldest limit , that is, its beginning, must be determined. The Carboniferous period, for example, began 360 million years ago, a milestone marked by the appearance of coal. So scientists must find a point where some material has emerged – rock or ice from a glacier, for example – to fix a pattern or GSSP (Global Boundary Stratotype Section and Point) that is marked with a golden nail, sunk in the rock, in order to indicate the stratotype in question .
On the cliffs of Itzurun beach, in Zumaia (Guipúzcoa), two golden nails mark the Danish / Selandian geochronological boundary (61.1 million years) and the Selandian / Thanetian boundary (58.7 million years). And they are not the only ones located in Spanish territory. On the Gorrondatxe beach, in Getxo (Vizcaya), there is the Lutecian stratotype (47.8-40.4 million years); in Fuentelsaz (Guadalajara), a section with more than 175 million years indicates the Aalenian floor; And, since November 27, 2015, the Olazagutía marl quarry, a place located in the Urbasa mountain range (Navarra), has been the world’s benchmark golden nail for the base of the Santonian floor.
Defining a GSSP for the Anthropocene is an atypical task, because it is not about studying the past, but rather about predicting the future. Nobody denies the magnitude of the human impact on the planet, but it is not easy to determine if it will remain on a geological scale . If tomorrow our species disappears, a million years from now, will there be a trace of our presence?
According to Zalasiewicz, “Geologists joke about the layer of fossilized Coca-Cola cans that we will leave behind. But, however drastic the effects may be on a local scale, determining a new epoch requires global and geologically significant evidence. ” It is about finding chemical or fossil markers that allow us to distinguish the changes between times within millions of years , when our world no longer exists. Although it is not part of the AWG, Crutzen does not stop commenting on it, and believes that some signals more than meet the requirements. In an article published in Nature, he states that the emission of polluting gases has altered the atmosphere so much that the global climate will deviate from its natural patterns for millennia . The disturbance will be easy to detect in the distant future.
There is no formal statement from the AWG yet, but many of its members agree with Crutzen, in light of some recent articles. In one of them, published in Science , it is stated bluntly that we have entered a new era . According to its main author, Colin Waters, from the British Geological Survey, “to formalize the Anthropocene we must assess whether the magnitude of the changes recorded is sufficient. After comparing what we observe today with the alterations that gave rise to the Holocene, we are convinced that this is so ”. Zalasiewicz, who was also involved in the study, adds that the start of the new geological period must now be established. There are already several proposals, but few meet the necessary requirements.
From colonialism to the atomic bomb
One of the most accepted hypotheses is that of William Ruddiman, paleoclimatologist at the University of Virginia, who affirms that the Anthropocene began 8,000 years ago , after the Neolithic revolution, when humans developed agriculture and livestock, became sedentary and he began to cut down forests for his crops . “These activities had dramatic effects on the climate by releasing huge amounts of greenhouse gases, long before fossil fuels were used,” explains Ruddiman.
Other experts have proposed dates as disparate as the year 1610, when there was a notable decrease in CO2 in the atmosphere as a result of the colonization of America by Europeans, which reduced the indigenous population and agriculture in the area; the beginning of the Industrial Revolution, at the end of the 18th century; the detonation of the first atomic bomb –July 16, 1945–; or the beginning of the great acceleration, the period of economic boom from 1950, marked by a population boom and many alterations in natural processes.
According to Waters, most of the AWG experts bet on some date in the middle of the 20th century: “In addition to climate change, in recent decades new materials that do not exist in nature have proliferated, such as aluminum or plastic, which will leave a significant footprint in the sediments . On the other hand, the construction of roads and large dams has altered the sedimentation regimes of very large areas, with patterns that will be visible millions of years from now. Few doubt that we are living a new geological interval, although there is still some debate about whether the Anthropocene should be a formal unit. “
Among the reluctants is Gibbard, one of the founders of the AWG. “I am not convinced. The interactions we have with our environment are increasingly complex but, from a geological perspective, I believe that what is happening is the logical continuation of the impacts caused by a gradual increase in human population since the early Holocene. I am not in favor of defining the Anthropocene as a division of geological time ”. Also according to some experts, in this discussion there is a key linguistic issue that is being ignored: “Copernicus displaced the human being from his privileged place in the middle of the universe. The Anthropocene puts it back at the center, ”says science historian and AWG member Naomi Oreskes.
Witnesses to a complex transition
And it is that, while the contemplation of the geological scale reveals the smallness of the human species , defining an epoch based on the Anthropos –’man’– gives us a new role, that of being fully responsible for the destiny of planet Earth. . This vision of the world will have unquestionable social, political, scientific and even economic implications. “It is a complex issue that should not affect our decision-making and that is the responsibility of politicians,” argues Waters.
“We must differentiate the approaches”, defends Syvitski. “The interest in the social implications of the Anthropocene – he continues – is independent of the research in geological aspects. Unfortunately, the scientific and humanities communities rarely talk to each other and the opportunity to raise awareness about the risks posed by current trends is not taken. “
Oreskes shares this view: “We are witnessing a complex transition. We want everyone to participate in the debate, but it is not our role to judge its implications. ” Be that as it may, civilization as we know it has gone down in history . If changes are not introduced and the problems that lie at the origin of this new term are not addressed, it is possible that our species and many others are doomed. The conclusions reached by the AWG experts will shape the way the planet is managed for years to come.
