A human golden spike?

The Holocene is our current official interglacial epoch, beginning 11,700 calendar years b2k (before AD 2000), marking the end of the Pleistocene Epoch (Walker et al 2009). This current interval is formally characterised by human activity, climate change, sea-level rise and more (Walker et al 2009), but most importantly marks the termination of the Last Glacial period, when glacial ice began rapidly retreating at the end of the Younger Dryas. Despite long being recognised at Series status, the Holocene was only formally ratified in 2008 by the IUGS as our current Epoch with a distinct stratigraphic marker (Walker et al 2009). 

This marker, a Global Stratotype Section and Point (GSSP), aka "Golden Spike" marks the lower boundary/beginning of a geological time unit (Lewis and Maslin 2015). The "spike" identified in strata of rock, ice, or sediment, for example, reflects a global-change phenomenon for a new unit of time. A really distinct example of a GSSP is the Cretaceous-Paleogene boundary, marked by mass extinction of dinosaurs 65.5 million years ago (Zalasiewicz et al 2011). Such a significant change in the Earth system like this is recorded clearly in rock records, providing a clean-cut boundary for a new interval of time. But what about more recently? The base of the Holocene is now officially defined by the NorthGRIP (NGRIP) ice-core from the Greenland ice sheet, with boundary level at 1492.45m depth in Borehole NGRIP2 (Walker et al 2009). 

The Holocene-Pleistocene boundary is identifiable here by measuring δ18O, marked by a shift to 'heavier' oxygen isotope values at the end of the Younger Dryas/Greenland Stadial 1 (GS-1) (Walker et al 2009).

Woah, woah, woah...I should slow down. Here I am talking about GSSP's and I haven't even told you about their (very!) strict criteria. Not just any old bit of rock, sediment, or ice will suffice. To have a geologic time unit approved by the big guys in the IUGS, Gradstein et al (2012) identify 7 key features for an appropriate GSSP:

1. A principal correlation event (the global stratigraphic marker)
2. Other additional secondary markers (auxiliary stratotypes)
3. Correlation on both regional and global scales
4. Complete continuous sedimentation above AND below the marker
5. An exact location at 1 point on Earth: longitude, latitude, depth/height
6. Accessible
7. The ability to be protected and conserved

We know the Holocene's GSSP meets these requirements, despite slightly differing from other markers in Earth History, due to being defined by a climatic signal in ice, as opposed to fossil evidence in rocks (biostratigraphic marker) (Walker et al 2009). But how does the Anthropocene stand up against this strict criteria? The Anthropocene Working Group are yet to come to a consensus for the onset of the epoch, let alone define a GSSP which meets the IUGS criteria.

From all the different suggestions of onsets for the Anthropocene (see this post for my quick summary), Lewis and Maslin (2015) suggest only two measure up with suitable accompanying GSSPs: the Orbis spike with a CO2 dip and minima in AD 1610, and the radioactive bomb spike in 1964 correlating with peak 14C. Rises in CO2 personally strike me as an obvious marker for the Anthropocene, though Zalasiewicz et al (2011) recognise that on longer timescales the changes, for example at the start of the Industrial Revolution, are too gradual to be recognised on an annual-decadal level.

With such difficulty in finding and agreeing on a robust GSSP for the Anthropocene, it has been suggested that a GSSA (Global Standard Stratigraphic Age) should be used instead. This would involve simply selecting a numerical age e.g. 1945, which marks a historical turning point for the Anthropocene-Holocene boundary: the Alamogordo test explosion (Zalasiewicz et al 2015). Though this may seem like an obvious alternate and simpler answer for the Anthropocene, many people have disagreed with the use of a GSSA for such a modern and developing time interval...

That's all for now, folks. Next time I'll be further discussing why there has been resistance for the use of a GSSA-based boundary for the Anthropocene.

Waiting Ages for Eons...

BOO! I hope you are all having a terrifyingly frightful Halloween!

The aim of this evening's post is to clarify the different geological time periods based upon how the IUGS International Commission on Stratigraphy (ICS) define them. We know the Anthropocene has been proposed as an epoch, but what does that actually mean?

Chronostratigraphy refers to the layers of rock (strata) which correspond to geochronologic time units. The official units in geochronology and stratigraphy (used by the ICS chart) are as follows, from largest to smallest in length:

EON
Chronostratigraphic unit equivalent: Eonothem
Examples: Hadean, Archean & Proterozoic (taken together as Precambrian), and Phanerozoic (current Eon)
Time Span: Indefinite length of time, but roughly billions of years +

ERA
Chronostratigraphic unit equivalent: Erathem
Examples: Paleozoic (old life), Mesozoic (intermediate life), and our current Cenozoic (recent life)
Time Span: Several hundred million years

PERIOD
Chronostratigraphic unit equivalent: System
Examples: Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary (current period)
Time Span: 30-80 million years

EPOCH
Chronostratigraphic unit equivalent: Series
Examples: e.g. Ogliocene, Miocene, Pliocene, Pleistocene, and Holocene (official present epoch). Does the Anthropocene belong here, too?
Time Span: Tens of millions of years

AGE
Chronostratigraphic unit equivalent: Stage
Examples: e.g. Campanian, Danian, Tortonian, Gelasian, Calabrian... maybe the Anthropocene?
Time Span: Lowest ranking unit, usually a few million years

(all information from the IUGS Stratigraphic Guide)

The ICS official geologic time scale as of 2015. If you can't read the writing (sorry), the original image can be downloaded here.

The Anthropocene is proposed as a potential geologic epoch, which would consequently terminate our current Holocene epoch. The Anthropocene would remain within the present Quaternary Period (which is in the Cenozoic Era, within the Phanerozoic Eon). From looking at other epochs in Earth History, they are pretty hefty chunks of time, so it is questionable whether the Anthropocene would suit this hierarchical level, or if perhaps instead it should become an Age within the Holocene...

Now you know what the different names for intervals of time actually mean, let's look at how long humans have been around for...

History of our planet Earth condensed into 12 hours. Though the start of the Anthropocene Epoch is subjective here to the author, the point remains that humans are just a blip in Earth History. (Source)

It's quite eye opening to realise that on this huge time scale, humans appear to be quite insignificant. If Earth's 4.5 billion years of existence were condensed into a 12 hour time period, humanity wouldn't exist until the last TWO SECONDS before midnight (almost like Cinderella..). However, in terms of effect on the planet in this short interval of time, humans have had a hugely disproportionate influence on the Earth. How can we already determine if humanity warrant an entire epoch, which might potentially last millions of years? Say, for example, that in the next century humans make home on our neighbouring planet, Mars. This (hypothetical, yet possible) planetary exploration might make a much greater defining signature for a human-dominated period of time. Or, perhaps the harnessing of nuclear fusion in a few decades might make a far more suited landmark for the start of a human-dominated age?

In my next post, I'll be exploring the evidence for the Holocene as our current (official) epoch, and discussing further whether the Anthropocene should be considered on the same hierarchical level. Hopefully this has given you some perspective on humans in Earth History and clarified the different terminology for geologic time intervals. And just because videos are far more entertaining than reading all this, especially on Halloween, check out the one below:

So catchy.

Earth's identity crisis...

Nature is having the mother of all identity crises. Our beloved planet is facing up to arguably some of the most unpredictable, unprecedented challenges it has yet to confront in its 4.5 billion year history. Never before has one single species had such a dramatic and powerful influence over nature itself.

Homo Sapiens have caused the rise of atmospheric CO2 levels to concentrations unprecedented in the last 400,000 years, warmed the planet, shifted sediment at 10x the speed of natural erosion, acidified the oceans, formed a hole in the ozone layer, contributed to mass species extinctions, and torn down millions of acres of forest each year for our use (Monastersky 2015). The fingerprint of humanity has never been so identifiable. We have stopped adapting to nature, and started forcing it to adapt to us (Syvitski 2012).

Are humans permanently altering the global environment? (Image: Occupy)

Welcome to the Anthropocene, otherwise known as 'The Human Age' (Monastersky 2015) A geological period like no other, characterised by humanity playing God, pushing Earth across sensitive planetary boundaries. Is this humankind's shining glory or worst nightmare?

Is this the latest chapter in Earth History?  (Image: Climatica)

The concept of the Anthropocene, though heavily contested, is one which has shaken and stirred the scientific community since its initial proposal earlier this century (Crutzen and Stoermer 2000, Crutzen 2002). Serious geological, environmental, and socioeconomic implications accompany this idea. We find ourselves asking, 'Could humans really be a geological force? Are we THAT powerful? If so, can we seriously be the cause of a new geological epoch?!' The answers to these questions are highly controversial, and thus form the bulk of my blogging exploration. Over the course of the next few months, I intend to delve into the intricate depths of the debates surrounding the Anthropocene with these key questions in mind:

• What impacts have humans had on the planet?
• Are these impacts of an epochal scale?
• When did the Anthropocene begin? Are we at its dawn, or at its dusk? Does this mean the end of the Holocene?
• Should the Anthropocene become an official epoch, or would it be better as only an age or event within the Holocene?

Instead of following a strict agenda, I hope this blog will be an engagement with the rapidly growing contemporary literature, allowing my views to mould as the blog progresses. Using academic papers, news articles, media outlets and any other sources that anger/intrigue/excite me, this blog will become a critical discussion of the evidence for and against the Anthropocene's formal ratification.

Ultimately, I hope to come to a conclusion whether or not I believe we are, already have, or should be entering the Anthropocene. As it stands, I am on the fence. Although humans have had undeniable planetary impacts, I am unsure if these are currently at an epochal scale. If, a few decades/centuries down the line, humanity further modified the biosphere, hydrosphere, cryosphere, lithosphere (and all the other spheres) to such an extent that Earth shifted into another stable climatic state...then I think that would be a much clearer stratigraphic signature to define a wholly new period of geological time.

However, the great thing about this blogging journey is that I am completely open to changing my opinion, and hopefully I'll change yours too! Perhaps it is these relatively large, detrimental effects we've had on the planet over such a short period of time that makes the Anthropocene such a pivotal current discourse. In January we'll revisit this initial post and see if my viewpoint has changed…

My next post will introduce the 'Anthropocene 101': the scientific basis, the key academic arguments, and a summary of the (very) contested suggestions for the onset of this proposed period. In the meantime, check out the short video below for a basic overview of some key ideas.

If this subject fires you up as much as it does me, please don't hesitate to vote in the poll and voice your comments below. I'm open to discussion. Do you think we're in the Anthropocene?

For now the jury is seated, Ladies and Gentlemen. Watch this space.