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Background On July 11, the Anthropocene Working Group (AWG) of the International Commission on Stratigraphy recommended that Lake Crawford in Ontario, Canada, be considered a "golden nail" to open a new chapter in geological history, marking the arrival of the Earth in the Anthropocene.

Little knowledge: stratigraphy "golden nail" Since the earth was formed 4.6 billion years ago, layers of rocks have been slowly covered on the original crust, leaving a "ten thousand books" made of stones for the evolution and development of the earth. In geology, these rocks are strata, and each stratum has its own geological age. How to accurately calibrate the "age" of strata? In the diligent exploration of scientists, the definition of "golden nail" came into being.

The official name of the "golden nail" is Global Stratotype Section and Point (GSSP), and the rock record at this point can clearly distinguish it from the previous geological age. Gold nails contain abundant information about stratigraphic events

According to the regulations of the International Union of Geological Sciences and the International Stratigraphic Committee,"Golden Nail" is the only mark to determine and identify the boundary between two eras of the world. Eon, generation, period, epoch and period on earth are distinguished by "golden nail". Once it is "nailed down" somewhere in the world, the place becomes an "international standard" of geological age.

Little knowledge: geological age geological age, generally related to relative age and absolute age.

The relative age of the earth is established mainly on the basis of fossils. Standard fossils of ancient animals and plants are mostly preserved in the strata of different periods. All kinds of animal and plant fossils appear sooner or later in a certain order, the lower, the earlier, the higher, the later. This is the "law of fossil sequence" proposed by British geologist Smith. So how do you relate time to fossils? We know that marker fossils or fossil assemblages vary from one age to another, so we can extrapolate the age of the strata from which they originated.

The absolute age of the earth is the actual number of years since the formation of rocks calculated according to the measured content of certain radioactive elements and their disintegration products in rocks. The older the rock, the older the age of the stratum.

What is the Anthropocene? The earth is about 4.6 billion years old. In order to describe the long period of earth history and major events in earth history, geologists and paleontologists divide the nearly 4.6 billion years of earth history into several stages according to the sequence of natural formation of strata. The time unit of the earth's age can be divided into epochs, generations, epochs, epochs and hours. For example, our current geological era is: Phanerozoic/Cenozoic/Quaternary/Holocene. The beginning of the Holocene was marked by the end of the last Quaternary glacial period 117,000 years ago. But a group of geologists wanted a completely new geological age to describe the effects of human activity on the earth, and they proposed the Anthropocene Epoch, the age of man.

As early as 1873, Italian geologist Stopani said that the earth had entered the "era of mankind." Except the term he used was "human generation." Later, the former Soviet geochemist Vladimir Vernadsky (1863-1945) proposed a more modern concept of "Anthropocene"-"Anthroposphere." Vernadez was also involved in the development of the Soviet atomic bomb, so he foresaw the ability of mankind to transform the world upside down. Unfortunately, this concept similar to the "biosphere" did not receive enough attention in Western academia at that time.

It wasn't until 2000 that atmospheric chemist Paul Crutzen (Figure 1, Paul J. Crutzen, 1995 Nobel Prize winner in Chemistry) began to popularise the term "Anthropocene," arguing that a new geological epoch had been formed due to the effects of human behavior on the Earth's atmosphere in recent centuries (Crutzen and Stoermer, 2021). Paul Crutzen's influence quickly brought the term "Anthropocene" to the fore, and the term "Anthropocene" appeared in more and more article titles.

Figure 1 Paul J. Crutzen, from the web An article from The Guardian details what happened next (Davison, 2019). At a meeting of the Geological Society of London in 2006, a stratigrapher named Jan Zalasiewicz suggested that he wanted to formally define the Anthropocene in geological time. But modifying the chronostratigraphic table, like adopting constitutional amendments at the national level, requires multiple rounds of proposals and deliberations within the International Commission on Stratigraphy-y (ICS). As a result, in 2009, the Subcommittee on Quaternary Stratigraphy of the International Stratigraphic Commission established the "Anthropocene Working Group" to investigate and define the "Anthropocene," chaired by Zarasiewicz. After 10 years of research, on May 21,2019,34 members of the Anthropocene Working Group voted on whether the Anthropocene should be recognized as a new geological age, with 29 voting in favor. So far, the team's next focus has been to identify the "golden nail" that distinguishes Holocene from Anthropocene (Figure 3,"golden nail" is the only global standard for geological classification of geological time strata, see Waters et al. (2018)).

Exhibit 2 Crawford Lake, Canada, from Block University Previously, the Anthropocene Working Group listed 10 candidate sites, including Sihailongwan Lake in northeastern China and Crawford Lake in Canada (Exhibit 2). But as the July 11 news said, Four Sea Dragon Bay Lake fell out of the list, and the Anthropocene Working Group nominated Crawford Lake as the "golden nail" of the "Anthropocene" at a stratigraphy meeting held in Lille, France and a press conference held in Berlin, Germany (McCarthy et al., 2023)The mud layer at the bottom of the lake records the increase in radioactive plutonium caused by the nuclear bomb test. If adopted, the proposal would be submitted to the International Commission on Stratigraphy and eventually to the International Union of Geological Sciences. At that time, if the proposal is finally approved, Crawford Lake's sediment core will mark the beginning of the Anthropocene.

Controversial "Anthropocene" Scientists have been hotly arguing over the term since it was first officially coined. At least two of these arguments are worth recalling:

1. Should the Anthropocene be established? Proponents argue that human activity has greatly exceeded natural variability itself. As the geologist Colin Waters said,"If you were in 1920, your perception of nature would be,'Nature is too big for small humans to change it'." "But that thinking has been completely upended over the past century, and the change in thinking has been as dramatic as a planet hitting the earth. Many studies have revealed significant changes in nature caused by human activities. For example: "plastic rocks" reported earlier this year (Figure 4,(Wang et al., 2023)As well as traces of radioactive debris from every human nuclear test (Figure 5).

Figure 4. Fernanda Avelar Santos. Some opponents argue that the changes being experienced are not so severe compared to cataclysmic events in Earth's history, such as the Cretaceous mass extinction 65 million years ago (which wiped out all dinosaurs and eventually led to the extinction of about 80 percent of the planet's species), and that human activity is just "loose organic matter about two centimeters thick." Others argue that the name Anthropocene may also have dangerous political implications. For example, possible human-induced warming has become a means of political attack.

The Anthropocene Working Group argues that human activity, especially after the Industrial Revolution, has become a geological force that has led to changes throughout the planet. We need a whole new unit of time to describe these changes. And these changes are not over yet, and human activities may have a greater impact on the planet in the future.

2. When should the Anthropocene begin? If the Anthropocene period is to be determined, it must be proved that the Holocene period has ended.

There are different opinions in the geological community about this time point. Some scholars have suggested that the surge in carbon dioxide concentrations in the atmosphere is a node, because humans 'heavy use of fossil fuels leads to increased carbon dioxide emissions. Other scholars have suggested using human-made objects as markers, such as plastic bags and ballpoint pens that will remain in the rock formation for millions of years. These remnants clearly distinguish them from previous geological ages. The alternation of geological ages is always accompanied by widespread extinction of plants and animals. So some scholars hope to determine the boundaries of the Anthropocene by counting human-caused extinctions.

A March 2015 Nature article on the definition of the Anthropocene suggested two possible dates for the Anthropocene, 1610 and 1964 (Lewis and Maslin, 2015). These two points in time represent the two Great Acceleration points of global civilization: the advent of the Great Age of Navigation and the high concentration of radioactive elements. In 2019, 29 scientists on the Anthropocene Working Group identified around 1950 as the starting point of the Anthropocene because it was the moment when mankind exploded its first atomic bomb. However, there were four negative votes in the two issue votes, which shows that there are still many voices of opposition and questioning (Davison, 2019). Opponents argue that linking the start of a new era to an atomic bomb ignores the fact that humans have been changing the planet for a longer time.

Does the Anthropocene really matter? Natural changes currently associated with the Anthropocene include habitat loss, global warming, concrete, plastic, etc. These changes will persist for millennia or more and gradually change the Earth system. So identifying the Anthropocene "golden nail" is not to determine the point in time of human activity on Earth, but to acknowledge the enormous impact humans have had on the planet. It makes sense to remind humanity of the geological impact of human social activities on the earth, and we must recognize this and find ways to deal with possible future crises."

But there is also suspicion that the push for formal recognition of the Anthropocene may have been more political than the pursuit of its geological significance. For example, from a geological point of view, the Anthropocene does not actually change at the same level as the Holocene. It can be the fourth period of the Holocene, i.e. Crawford period after Greenland period, Northgribian period and Meghalaya period, but it is obviously not as remarkable as the Anthropocene (Davison, 2019).

To sum it up in Colin Waters 'words, the Anthropocene means that' humanity 'itself has become a geological process. This sentence reminds me of the last overlords of the earth-dinosaurs. In any case, as time passes, human eras, including you and me, will always enter the geological chronology. But I am more curious than that: dinosaurs may have evolved into chickens (Asara et al., 2007)What about the future of mankind?

references

Asara, J.M., Schweitzer, M.H., Freimark, L.M., Phillips, M., Cantley, L.C., 2007. Protein sequences from mastodon and Tyrannosaurus rex revealed by mass spectrometry. 316, 280-285.

Crutzen, P.J., Stoermer, E.F., 2021. The 'Anthropocene'(2000). 19-21.

Davison, N., 2019. The Anthropocene epoch: have we entered a new phase of planetary history? 30, 2019.

Lewis, S.L., Maslin, M.A., 2015. Defining the anthropocene. 519, 171-180.

McCarthy, F.M., Patterson, R.T., Head, M.J., Riddick, N.L., Cumming, B.F., Hamilton, P.B., Pisaric, M.F., Gushulak, A.C., Leavitt, P.R., Lafond, K.M., 2023. The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series. 10, 146-176.

Wang, L., Bank, M.S., Rinklebe, J.r., Hou, D., 2023. Plastic-rock complexes as hotspots for microplastic generation. 57, 7009-7017.

Waters, C.N., Zalasiewicz, J., Summerhayes, C., Fairchild, I.J., Rose, N.L., Loader, N.J., Shotyk, W., Cearreta, A., Head, M.J., Syvitski, J.P., 2018. Global Boundary Stratotype Section and Point (GSSP) for the Anthropocene Series: Where and how to look for potential candidates. 178, 379-429.

This article comes from Weixin Official Accounts: Stone Science Popularization Studio (ID: Dr__Stone), author: Ye Xiangying

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