This question has more than one answer. There are multiple interpretations of what “Anthropocene” means, a complication to which I will return in subsequent posts. Here I focus on the use of “Anthropocene” as a geological term.

Over its history the Earth’s surface has been repeatedly transformed by large-scale changes in climate, atmosphere and ocean chemistry, volcanic activity, and the biosphere and, more recently, as a result of human and technological activity. Debris from each phase of Earth history is buried and eventually lithified, or turned into rock. Traces of these changes in Earth function are often preserved as chemical, physical, or biological signs in the resultant rocky layers. Geologists who study such layers or “strata”—stratigraphers—are able to read the rock record, and thus interpret what the Earth has been doing over the course of its long lifetime. Lately, they have been finding strange new signs, like plastic and exotic radionuclides. These are signs of the Anthropocene.

Lately, they have been finding strange new signs, like plastic and exotic radionuclides. These are signs of the Anthropocene.

An internationally agreed-upon Geological Time Scale was developed to help keep all this information well-organized and easy to communicate. Terms like Jurassic, Paleozoic, and Carboniferous are examples of geological time intervals. “Anthropocene” is presently under consideration as the “next” or “newest” addition to the Geological Time Scale, reflecting large scale human- and technology-driven modifications to the fabric of the Earth.

There is no set rule for choosing names. The Jurassic Period is named after the Jura Mountains, lying along the French-Swiss border. The Paleozoic (think “old zoo”) Era denotes a time early in the tenure of animals on the plant. The Carboniferous Period refers to a time of abundant vegetation whose carbon-rich remains contributed to what became major coal-bearing beds of the world. The name “Anthropocene” came to wide attention when, at an international conference, the chemist Paul Crutzen called out the name in frustration over continued use of the then (and still) official term for the current interval of geological time, the Holocene Epoch (1). “Holocene”, meaning “wholly new”, refers roughly to the time since the end of the last Ice Age. To Crutzen, continued reference to the “Holocene” seemed wholly inappropriate when modern anthropic influence on the Earth was such a pervasive topic in discussions at the conference. The implication was that Earth processes had undergone a sea change in the latter part of the Holocene, marking the planet with a unique signal that merits its own distinctive terminology in the geological timeline, the “Anthropocene”.

The implication was that Earth processes had undergone a sea change in the latter part of the Holocene, marking the planet with a unique signal that merits its own distinctive terminology in the geological timeline, the “Anthropocene”.

Official geological time intervals come labeled with qualifiers like Era and Period. These denote a hierarchy in time scale. The lengths of geological intervals are not standardized, like seconds and minutes, because they refer to episodic changes in planetary environments whose time of occurrence varies according to complex causes. Major interval classifications in the Geological Time Scale include Eon, Era, Period, and Epoch. Like the hierarchy in a set of Russian dolls, long Eons contain shorter Eras, which in turn contain Periods and then on down to Epochs (and if one keeps going, finally down to Ages), with the longer intervals indicating enduring planetary conditions on which the shorter intervals are variations. For example, the Phanerozoic (“visible life”) Eon, in which we live today, corresponds roughly to the reign of animals, with the Paleozoic Era representing its earliest part.

The geological Anthropocene, even though unofficial, is usually spoken of as an Epoch; if officially adopted as such, the tail of the present Holocene Epoch would be docked, and the Anthropocene Epoch attached as an open-ended time interval with no specified termination point (as is the case for the present Holocene). The reason for suggesting an epochal designation for an Anthropocene time interval, rather than a more august label like Period, reflects an inherent (and usually justified) conservatism in stratigraphy when contemplating any modification to a chronological scheme on whose stability the international geological profession depends for interpreting Earth history. The evidence to support making a change needs to be substantial. (The case for inducting the Anthropocene Epoch into the official register of geological time is summarized in (2).)

Because geological strata are laid down in chronological order, the progression from Eon down to Epoch is reminiscent of the chapters, sections, subsections, and finally pages of a book. The title of this book is The Autobiography of the Earth. As the name suggests, the book was not written by humans, but by the planet itself. It thus holds many secrets in its pages to which humans are not yet privy. These involve not just the history of rock, but, to be discerned in the fine print and footnotes, the history of water, the history of air, the history of life, and the history of humans, society, and technology. Many original pages are missing, the information they contained erased by processes of erosion and underground transformation (rewriting).

Much recent history has already been typeset in Earth’s stratigraphy. The resulting text constitutes what the Earth has composed so far about the events of the Anthropocene Epoch. But the book is still being written, with much information still scribbled in manuscript form, not yet sent to the printer to find its place in the book’s newest chapter, The Anthropocene.

But the book is still being written, with much information still scribbled in manuscript form, not yet sent to the printer to find its place in the book’s newest chapter, The Anthropocene.

It is worth noting that what the Earth writes about any time interval, and the time interval itself, are two separate things. The first refers to the physical record of events (the Earth’s chronostratigraphy) generated during the time interval, often in the form of lithified debris. The second is the name we give to the actual time interval (the Earth’s geochronology). The physical record corresponding to an epoch is called a “series”, for example the Anthropocene Series; the time interval itself is, in this case, the Anthropocene Epoch. For the most part we do not need to worry here about this distinction. However, the need to qualify “Anthropocene” even when discussing purely geological questions prefigures the complications that arise when “Anthropocene” is adopted by multiple disciplines in reference to particular world-views. We touch on the issue of multiple Anthropocenes, including the political and social Anthropocenes, later in this essay.

Finally there is the question, who or what is writing the Anthropocene entry into the book of Earth? Above I argued that the Earth is writing its own book. However, it may seem to many readers that, even if true over most of Earth history, the situation in Anthropocene times is different. Surely humans are the principal authors of Anthropocene events. After all, doesn’t the word “Anthropocene” refer to humans? And aren’t humans responsible for the novel forms of debris that contribute to the Anthropocene Series, and thus the information encoded on the most recent page of the book? On closer inspection it turns out that the answer to this last question is not a simple “yes”. One of my main objectives in this essay is to show why this is the case.

Further reading
(1) Paul Crutzen describes his view of the Anthropocene: Paul Crutzen (2002) “Geology of Mankind”, in Nature Volume 415, page 23.

(2) Why the geological Anthropocene merits formal recognition: Jan Zalasiewicz and others (2017) “Making the case for a formal Anthropocene Epoch: an analysis of ongoing critiques” in Newsletters on Stratigraphy, Volume 50, pages 205–226.

Persistent citation for this post: P. K. Haff, 2.1 What is the Anthropocene?, in Being Human in the Anthropocene blog, 2018. https://perma.cc/96TS-HZ85.

Next up: Does the modern Earth warrant recognition in The Geological Time Scale? I will look at some reasons for adopting the Anthropocene Epoch as a formal unit of the Geological Time Scale.