As earth scientists began to better understand and read Earth’s history from the detailed chemistry and ages of various rock formations and the fossils within them, they found that Earth’s history could be divided into different ages which they called “Eras.” As more was learned they divided Eras into different “Periods” and then divided the different Periods into different “Epochs.” Major events in Earth’s history such as massive biological extinctions left their mark not only in the specific collections of fossils found within these layers but also in the chemical and physical characteristics of the layer itself. These major events were then used to mark the boundaries between the geologists’ Eras, Periods, and Epochs. This whole exercise makes it easier for geologists to communicate with one another and ultimately construct a more coherent geologic history of our planet. The current Era (the Cenozoic) began about 65 million years ago at the time dinosaurs abruptly became extinct (as a result of our collision with a large meteorite and possibly as a result of a massive outpouring of lava as well). The oldest Period within the Cenozoic is currently called the Paleogene (65 to 23 million years ago) and the latest Period (23 million years ago to the present) called the Neogene. The Epochs within the Neogene Period are known as the Miocene, Pliocene, and Holocene, respectively. The Holocene Epoch began as the Earth’s most recent glacial period ended and our Earth embarked on another warm spell (about 10,000 years ago and coinciding with the beginnings of agriculture). Now, as we learn more about the considerable impact humans are having on our planet, many Earth scientists have urged that we refer to our present geologic age as the “Anthropocene Epoch.”
Some of those who favor this new designation believe its beginning should be set as the start of the industrial period (about 200 years ago). However, recent research has indicated that atmospheric carbon dioxide (CO2) began to increase, albeit slowly at first, some 5,000 years ago, a phenomenon not seen in prior interglacial periods, and well before it’s more dramatic rise beginning around 1,800. Coincidently, new and more careful research on early farming practices has raised the strong possibility that early farmers cleared much more land per capita (often by burning) than did later farmers. Thus it may have been this widespread clearing in Europe, Asia, and the Middle East that accounts for this early rise in atmospheric CO2. Certainly forest clearing for wood, pasture and crops is among the larger alterations of Earth’s ecology that can be attributed to man.
If this new data holds up, it may mean that our Anthropocene Epoch will be said to have started some 5000 years ago. But given the evidence that the extinction of many large plant-eating mammals was likely at least a partial consequence of human predation beginning about 40,000 years ago perhaps it would be more logical to discard the Holocene Epoch altogether and place the start of the Anthropocene Epoch at least as far back as the end of the Pliocene Epoch. In any event, we can be sure it will be some time before any renaming and dating of our current Epoch is generally agreed upon by geologists.
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