Classification is a human game. Why do we have a "Cambrian era"? Only because Adam Sedgwick decided to give certain rocks in Wales that name. Piece by piece, eras, epochs and periods were added from different locales, given local names, to form a man-made picture of earth history that only roughly corresponds with the rocks. Other civilizations at other times could have had completely different names and categories for the same strata, carving them up in completely different ways.
The same goes with biological classification: those started with Linnaeus, and became more elaborate with attempts to fit all plants and animals into his scheme. It's not that connections to reality are lacking. It's that such schemes can only imperfectly "carve nature at its joints." Classification schemes are man-made tools that help scientists speak a common language. They are only as good as they are useful. Sometimes, though, they stifle thinking by forcing data into predetermined categories that may or may not encourage open-minded inquiry.
We're seeing a new example of the philosophy of classification happening now. Some geologists, biologists and social scientists think it would be useful to create a new time period to designate the onset of human modification of the planet. This would work well, for instance, for climate scientists wishing to pin the blame on humans for climate change. So, here comes The Anthropocene Epoch.
That last headline points out a question: when did the Anthropocene begin? Geologists look for a "golden spike" to designate the onset of each new epoch. So where should they designate the beginning of this period? The Anthropocene Working Group (AWG) is working on it.
"The majority of us think it is real; that there is clearly something happening; that there are clearly signals in the environment that are recognisable and make the Anthropocene a distinct unit; and the majority of us think it would be justified to formally recognise it.
The BBC and Live Science articles illustrate the new epoch with photos of atom bombs exploding. Will 1945 mark the Golden Spike? We know that radiocarbon dates have to be adjusted because of anomalous readings from above-ground atomic tests. Clearly there are indicators that man has altered the planet. But haven't many other organisms done that, too? Microbes are thought to have changed earth's atmosphere. Does each organism get its own epoch? Did the Anthropocene even exist before someone decided to come up with the name? Why did they use Greek (anthropos) for the name instead of Latin? It's all arbitrary, tentative, and conventional, useful only to the extent it advances human understanding.
Classification points out an important aspect in the philosophy of science. Human names and categories are not "real" outside of the human mind. Rats don't have a Ratocene Epoch. Trilobites don't refer to their heyday as the Cambrian. This is not to say that names are not useful. Adam's first job was to name and classify the animals. That's what humans do. It's evidence of our intelligence. To the extent that our names help us organize our thoughts, great. But we tend to reify our concepts, bestowing on them an existence outside of our minds. This can mislead as well as enlighten. The "Pennsylvanian" is not "real" in the Grand Canyon; that's just a name geologists call a certain section of strata typified by certain kinds of fossil assemblages. Can we be certain of correspondence to similar strata in China? Not exactly. Usually things don't fit neatly, requiring auxiliary hypotheses to account for anomalies.
The Geologic Column, reproduced in many a textbook, tends to force-fit discoveries into the evolutionary mold. Good scientists must be willing to think outside the box. If the data don't fit, say so! Problem is, you may have a terrible time getting enough peers to follow your ideas. Once names are established, it's awfully hard to change the textbooks. And it's hardly useful for Americans to call strata by one classification and Russians to call it by a different one. Change may take a scientific revolution. So what? If a revolution is merited, there's no ironclad law saying paradigms must never change. Keep piling on the anomalies bravely if you find them. Never be afraid of being a maverick. Follow the evidence where it leads. Scientific revolutions are hard, especially when they are supported by ideology and fossilized consensus. Truth should be a bigger priority than the schemes and scenarios of human convention.