"Human activity is leaving a pervasive and persistent signature on Earth." So begins one of the more depressing scientific papers I've ever read.
What follows in "The Anthropocene is functionally and stratigraphically distinct from the Holocene," a new study published in Science, is a laundry list of human sins that, in total, add up to what its authors say is irrefutable evidence that Earth has entered a human-driven geological epoch that began midway through the 20th century and continues today.
Whether we're actually living in the Anthropocene (the era of humans, basically) rather than a subdivision of the Holocene, an era that started roughly 11,700 years ago, has been a subject of great debate in scientific circles for the last two decades. Some argue that the Anthropocene started when humans first began making fires and polluting; others have traced it back to around 1610, when European settlers began earnestly making their mark on the Earth as a whole. Still others suggest that humans aren't capable of making a geologically significant impact on Earth. Or at least they're not yet.
The paper, published Thursday by 24 well-respected scientists from the Anthropocene Working Group (whose members include scientists from the British Geological Survey, Cambridge University, Berkeley, the University of Nairobi, Harvard, Georgetown, Duke, the Australian National University, etc. etc. etc. and so on) argues that the Anthropocene started in the mid 20th century.
If the study is officially recognized by the International Commission on Stratigraphy, the authors say that "not only would this represent the first instance of a new epoch having been witnessed firsthand by advanced societies, it would be one stemming from the consequences of their own doing."
As you might suspect, the driving force behind these changes are "accelerated technological development, rapid growth of the human population, and increased consumption of resources."
Let's take a look at the evidence.
Influence on rock layers (strata)
The authors note that "recent anthropogenic deposits, which are the products of mining, waste disposal (landfill), construction, and urbanization contain the greatest expansion of new minerals since the Great Oxygenation Event [2 billion years ago]."
The findings are "entirely novel with respect to those found in the Holocene and pre-existing epochs"
More than 98 percent of all elemental aluminum (the metal is not naturally occurring) has been produced since 1950, and the past 20 years account for more than 50 percent of all concrete ever created. The biomass of plastics we've manufactured now weighs at least as much as the combined weight of all the human beings on Earth, and "the decay resistance and chemistry of most plastics suggest that they will leave identifiable fossil and geochemical records."
Modification of land surfaces
Dams, mining activities, and landfills have "modified sedimentary processes sufficiently to leave clear expressions in river, lake, windblown, and glacial deposits that are often far removed from direct point sources." Meanwhile, agriculture and livestock farming has transformed countless biomes around the world and deforestation in the tropics has necessarily influenced the construction of mountain roads that "is resulting in substantial surface erosion and landslides."
New geochemical signatures
Pollution, farming, and energy use (coal, gasoline, etc) have resulted in nitrogen and phosphorus levels doubling in soils over the last 100 years. "Human processes are argued to have had the largest impact on the nitrogen cycle for some 2.5 billion years." Use of rare earth elements since World War II has resulted in "a global pattern of dispersion in the environment and novel stoichiometric ratios," while "industrial metals such as cadmium, chromium, copper, mercury, nickel, lead, and zinc have been widely and rapidly dispersed since the mid-20th century."
We of course haven't even gotten into the fallout from nuclear bomb testing, which, according to the authors, is "potentially the most widespread and globally synchronous anthropogenic signal." The scientists note that the fallout "will be identifiable in sediments and ice for the next 100,000 years."
Carbon cycle and sea level rise
The researchers write that atmospheric carbon, which is now over 400 parts per million, "was emitted into the atmosphere from 1999 to 2010 ~100 times as fast as the most rapid emission during the last glacial termination."
Most frightening, perhaps, is that Earth should be cooling due to its current orbit cycle around the sun, however, "increased anthropogenic emissions of greenhouse gases have instead caused the planet to warm abnormally fast, overriding the orbitally induced climate cycle."
The scientists note that we are likely in the beginning stages of a sixth mass-extinction event, but that "evolution and extinction rates are mostly too slow and diachronous to provide an obvious biological marker for the start of the Anthropocene." The planet does, indeed, still host most of the species that we began the Holocene with. However, we can still use species distribution to mark human impact on the Earth: "Species assemblages and relative abundance have been altered worldwide," they wrote. "This is especially true in recent decades because of geologically unprecedented transglobal species invasions and biological assemblage changes associated with agriculture on land and fishing in the sea."
Taken together, the findings noted above are "either entirely novel with respect to those found in the Holocene and pre-existing epochs or quantitatively outside the range of variation of the proposed Holocene subdivisions."
In other words, welcome to the Anthropocene, fellow human.