Geological time is divided into various lengths and kinds of sections. This is to make it slightly easier for people to understand what we’re talking about. Everyone (now) knows that when you say Jurassic, it has something to do with dinosaurs. Used to when I would say that, people just looked at me funny. Trust me, standing on a street corner yelling “Jurassic!” will get you all kinds of attention.
There’s all kinds of cool posters showing geologic time, I mean, who wouldn’t want this on their wall? (here’s a readable PDF)
You can get one like this here: The Geological Time Table, Sixth Edition
These time scales are chosen based on significant events that occurred at the beginning, ending, or during the time period. Probably the most well known is the K/T extinction. K is the symbol for the Cretaceous period and T is the symbol for the Tertiary period (which is somewhat out of date, but still in use in, for example, the K/T event).
The K/T boundary (at about 65 million years ago) marks the last time non-avian dinosaurs existed on Earth. That’s a pretty significant event since dinosaurs had pretty much locked up planetary dominance for nearly 200 million years.
So, the boundaries are events of some significance. There are lots of these boundaries. Some are based on biology and ecology (like the K/T event) and some are based on climate or geological events.
Take a look at the upper left on that chart. Inside the Cenozoic Era, in the miniscule time period of the Quaternary, at the very top of the epochs, there is a tiny little time slice called the Holocene. That’s where we are. The Tertiary used to exist between the Quaternary and the Cretaceous, in case you’re curious.
The Quaternary is characterized by the presence of humans and a series of glaciation/warming events. So, that little yellow time slice (compare to the entire Mesozoic) is how long humans have existed.
Of course, modern humans (by this I mean with technology) have been around for a much shorter time frame. And some archaeologists are saying that we are really in another, new epoch. The Anthropocene, that is, the age when man began to alter the world to suit himself, instead of just trying to survive in a hostile world.
The archaeologists are saying that the invention of farming may have been the beginning of this new age. Alternately, even 60,000 years ago, hunter-gathers were wiping out the animal populations of islands and certain areas of the continents. Who am I to argue… well… since you insist.
Certainly killing huge numbers of large wildlife is a significant event… to a human (or the animals in question). On a global scale and on a geologic timescale, it’s not significant at all. A major disease could wipe out an entire species in very little time and we think we know of a species that this almost happened to.
I would submit that farming, by itself, is not a major enough change. The creation of giant cities of stone which required the shipping of food to farms is what I would consider a large enough change. To me, a few herdsmen planting some seeds and, in a few months, wandering back through the area and finding those plants with some food on them is little more than just promoting the growth of certain plants.
But when you get to large stone cities, whose foundations and debris will remain in the Earth for centuries, you start to see a different system. You begin to see the wholesale removal of large swaths of forest to support farms. You begin to see road networks that (in some places) still exist to this day. You begin to see specialists and, soon, a technic society.
That is the critical juncture in my, admittedly non-anthropologist, opinion. I would suggest (and some have before me) suggest that the beginnings of the industrial revolution as the time for the new epoch to begin. That is the critical juncture in which we began not just to hide in the dark and hope the wolves would stay away, but began to go out and kill the wolves.
During this period we began killing off not just one or two species on a local level, but mass extinctions of all kinds of species, from the very smallest (smallpox for example) to the the largest (western black rhinoceros, for example).
It is after the industrial revolution that we humans began to alter the climate. We are causing such a change in the temperature via carbon dioxide that an intelligence that looks at the geological record will be able to see the spike we’re causing.
Our technic society is creating structures that will last as long, if not longer, than major rock formations. I’m referring here not to single building, but cities. Los Angeles is 500 square miles of nearly uninterrupted concrete, New York is only slightly smaller.
Another report (here) highlights that we are the cause of some new kinds of rocks.
Here, we report the appearance of a new “stone” formed through intermingling of melted plastic, beach sediment, basaltic lava fragments, and organic debris from Kamilo Beach on the island of Hawaii. The material, herein referred to as “plastiglomerate,” is divided into in situ and clastic types that were distributed over all areas of the beach. Agglutination of natural sediments to melted plastic during campfire burning has increased the overall density of plastiglomerate, which inhibits transport by wind or water, thereby increasing the potential for burial and subsequent preservation. Our results indicate that this anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the informal
These authors think it will come later than I even do. If their suggestion holds, even I will have lived during the transition from one epoch to the next. Pretty awesome… but for very wrong reasons.
The Anthropocene is proposed to become official in 2016. The scientists suggesting the new epoch are not going to just randomly decide on when it began, but look at data from geology, anthropology and biology to make the decision. Whatever the decision, I hope that it serves to reinforce the idea that we are not non-disruptive riders on the planet. We’re altering the planet, yes to suit us better. But we really had no idea what we were doing. Now that we do, it’s time to start thinking of ways to correct our mistakes.
Corcoran, P., Moore, C. & Jazvac, K. An anthropogenic marker horizon in the future rock record. GSA Today 48 (2014). doi:10.1130/GSAT-G198A.1
Mihram, D. & Mihram, G. The AAAS 2011 Annual: Science Without Borders. Library Hi Tech News 28, 713 (2011).