All posts tagged rocks

What is the rationale for creating a whole new epoch called the Anthropocene? Is there any reason to think Earth has changed or is changing so much or so fast that we are in a span of time different from the Holocene?

The geological time scale was first developed in the 19th century to divide up geological time. This time scale continues evolving as new methods of determining the dates of the rock strata allow for more and more precision. The broadest division of geological time is the era—the Archean is the oldest, and the Cenozoic the youngest. Eras are divided into periods: the Cenozoic is divided into the Paleogene, Neogene, and Quaternary. The Quaternary is currently divided into two epochs: the Pleistocene (pleistos is Greek for “most”) and the Holocene (holo- is for “whole, complete”). The smallest category is the age: the Pleistocene epoch includes four ages—the Holocene, being relatively short, has not been divided into ages. The latest stratigraphic chart (updated in January 2013) [1] places the beginning of the Holocene at 11,700 years ago; that date reflects the end of the last major glacial epoch. Considering that Earth has now been found to be 4.57 billion years old, the Holocene seems a mere blink of an eye.

What has led scientists to consider declaring a new epoch? Why should this be done soon and not a few centuries or millennia from now? After studying the subject, I will try to answer my first question, but I am not sure anyone can answer the second, unless the answer is that humans may not be around long enough to care about such things.

The first half of the 19th century was an important time for people who cared about Earth and how it may have been changing before they were born. Georges Cuvier (1769–1832) helped start the discipline of paleontology, which establishes units of geological time by studying the differences in fossil remains. He also recognized as early as 1812 that some thing or things (presumably floods) had caused mass extinctions. Another Frenchman, Jean-Baptiste Lamarck (1744–1829) developed the theory of inheritance of acquired characteristics. Later, two English friends, geologist Charles Lyell (1797–1875) and Charles Darwin (1809–1882) had the strongest influence on scientific thought for some hundred years, both believing that changes occurred gradually and extermination of species had always been a slow process. Still, the fossil record clearly showed there were periods when flora and fauna of certain types had quite suddenly disappeared, and very different types of critters had appeared practically overnight.

By the latter part of the 20th century, stratigraphers and other geoscientists had proven that major and quite sudden mass extinctions had occurred five times between about 440 million years ago (mya) and 65 mya, and there were many less-drastic extinctions. Now geoscientists and anthropologists are pondering whether we are plunging headlong into a sixth extinction. If so, what is causing it? How fast is it happening? Is it inevitable or can we act to slow, halt, or reverse it? If we are in a new epoch, just when did it begin? These are some of the questions that must be answered.

Let’s look at evidence of how humans have “altered the course of Earth’s deep history,” as expressed by paleontologist Jan Zalasiewicz of the University of Leicester, U.K., and his colleagues [2]. Take human population: huge increases have occurred in a short span of time (about the last two hundred years); with the consumption of fossil fuels, megacities have grown larger and larger; world population may reach 9 billion by 2050. In a record trapped into Antarctic ice that is almost a million years long, we can trace the recent rapid acceleration of chemical and biological effects on Earth. The increase in worldwide temperatures is causing changes that are unprecedented in their extent, severity, and speed, such as the rise of sea levels, species migration and extinction, and ocean acidity.

To name two of the chemical effects lumped together by Zalasiewicz, there are the well-known effects of excessive carbon dioxide on the atmosphere and the fact that black carbon particles, falling out of the air continually and appearing even in Arctic ice, are now classified as a major human carcinogen, in addition to their effect on climate. These were mentioned by Sybil Seltzinger of the International Geosphere-Biosphere Programme (IGBP) when she spoke at AGU.

I had been pondering these subjects for some time, but a very accessible article related to such questions fell into my hands late last month and precipitated my writing this essay. I read the two articles titled “The Lost World,” by the excellent New Yorker staff writer Elizabeth Kolbert [3]. To Zalasiewicz’s list of effects on Earth traceable to human actions she adds another of his favorite subjects—rats. Rats “have followed humans to just about every corner of the globe, and it is his professional opinion that one day they will take over the earth.” Kolbert has expanded her 2009 article, “The Sixth Extinction,” into a book of the same name to be released next month.

My next post in this Anthropocene series will continue on from pointing out some ways humans have changed the Earth to whether we can counteract any of these effects and why we should care.

References

[1] The stratigraphic timescale: http://stratigraphy.org/index.php/ics-chart-timescale
[2] Zalasiewicz, J., Williams, M., Steffen, W., and Crutzen, P. “The New World of the Anthropocene,” in Environmental Science and Technology: www.pubs.acs.org/doi/full/10.1021/es903118j
[3] Kolbert, E. “The Lost World,” in two issues of the New Yorker, December 16 and 23/30, 2013.