The Anthropocene - Time for a New Epoch?

If you weren’t human, and you were looking even casually at the geologic record for the past few hundred years (be it hard rock, ice cores, biota fossil patterns, etc.), you could classify a huge number of things as being purely “anthropogenic” in nature. We have made some unique signatures on the geological record, even if some claim we won’t leave much of anything if we disappeared. The artificial synthesis of ¹⁴C during atmospheric nuclear tests, the increase of mercury into the atmosphere, and all those species we’re unrelentingly killing off are just part of the mark we’re leaving on the rocks currently being deposited and formed. If you view Humans as another part of nature, as you should from a purely scientific perspective, you can simply regard our effects on nature as just another set of natural processes. So I agree that the Anthropocene should be considered as an epoch.

But to be clear, what defines an epoch, an age, a period and era or an eon in the geological sense is reasonably arbitrary. There is nothing in particular one must consider as a marker between two periods. Time periods can be determined as the time when a particular large group of biota become extinct (like the P-T extinction event) or when there’s enough cooling for rocks to form and then for some of those rocks to still exist (like the Hadean-Archean boundary). A geological time is defined by geologists saying “that’s a good point right there because of this”, and nothing more. Brain at Clastic Detritus has an article expressing how annoyingly wrong a news article got this particular point.

In his latest article, The Anthropocene revisited, Andrew Alden takes another look at the concept of recognising the remarkable changes the human species has had on the geological record as a new geological epoch (Universe Today also has a good article up on this topic). The concept of the Anthropocene, as originally suggested by Nobel Prize-winning chemist Paul Crutzen in 2002 is discussed in a (freely available) GSA Journal paper entitled “Are we now living in the Anthropocene“, which I quote below;

A case can be made for its consideration as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change.
Zalasiewicz et. al., 2008

The current “sixth mass extinction” event we are causing started in the Holocene, the epoch that is defined as the 10,000 carbon years preceding 1950 (Zalasiewicz et. al. 2008, Wikipedia). This was the end of the Younger Dryas, the name given to the last ice age, and saw the beginning of the widespread extinction of mega fauna such as the Mammoth and the last Saber Tooth Tiger species. This, much like the extinction event at the Cretaceous-Tertiary boundary, began and continued slowly (in human terms) until a single event established it as a true geological boundary (and I’ve discussed this particular point before). It was a slow process. It began slowly (say, over a period like 10,000 years), and then ended suddenly (over a few months, but a few decades is basically the same in geological terms).

Though establishing a new epoch is probably best in terms of scientific enquiry, it would make the dawn of human domination of the Earth (the Holocene) a separate epoch from the widespread changes that domination brought with it. And if you consider the human phenomenon as a single natural process, it may make more sense to consider the beginning, duration and end as a single time period. And not to put too finer point on it, I think the amount of change currently occurring is so dramatic that establishing a new epoch maybe underplaying it. Should we begin to consider the establishment of a new Period once we can no longer sustain ourselves to cause as much change as we are currently? That being said, I’m in favour of considering everything since a yet-to-be decided point (and by point, I mean a very precise, slightly un-geological point, like new years eve 1850), as a new epoch, even if it does make the Holocene the shortest geological epoch ever. To be fair, I’m more interested in pre-Hadean events than the latter parts of the Quaternary.

References

• Zalasiewicz J, Williams M, Smith A, Barry TL, Coe AL, et al. (2008) Are we now living in the Anthropocene. GSA Today: Vol. 18, No. 2 pp. 4–8