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.

"The scheduled service to the 'Next Ice Age' is delayed..."

There is change afoot at Earth station central, where humankind appear to be rewriting the timetables. Trouble is, this could be inviting unforeseen circumstances further down the line...

Imagine one morning, you wake up (or rather, you don't), buried under 10 feet of snow. You desperately fight your way to a window, a gap in the snow, anything which allows you to look outside. Searching for a familiar landscape of rolling green hills and townscape, instead you find a barren, desolate, ice-covered horizon. Am I dreaming, you think? What has happened to planet Earth as we know it?

The Ice Age which never arrived - artificial scenes from The Day After Tomorrow (Source)

Well, this (slightly dramatic) scenario could have been a cold, hard truth for humanity over the next millennium, though not taking place on the overnight time-frame as suggested in films like The Day After Tomorrow. Ever since humans started inadvertently tampering with the CO2 dial in the atmosphere, Earth's future path has veered somewhat off-piste. Before copious layers were sewn to a seemingly ever-growing blanket of greenhouse gases in the atmosphere, it is believed the planet was en route to a new ice age. Now, however, this glaciation isn't likely to happen any time into the foreseeable future, and it's because of humans.

Research led by Chronis Tzedakis, a professor at UCL, has suggested that the onset of a new ice age would begin in 1,500 years time, IF (and this is a very important 'if') CO2 concentration were still at pre-industrial level (~280 parts per million (ppm)). Since the dawn of human civilisation, increased agriculture, the industrial revolution, and the most recent Great Acceleration period (see my last post), CO2 has risen to an average today of almost 400ppm, nearly double the threshold of ~240ppm required for glaciation! Even if anthropogenic emissions were shut down tomorrow, it would take a considerable amount of time to bring atmospheric CO2 concentrations down enough to support a big freeze.

Interglacial-glacial cycles are largely controlled by the slow, cyclical changes in the nature of Earth's orbit around the Sun. These are called Milankovitch cycles, and take place on timescales of tens of thousands of years. A key trigger for ice age inception is weak insolation (low heat from the Sun) during the summer months. Tzedakis et al (2012) compared present day to an interglacial 780,000 years ago, Marine Isotope Stage (MIS) 19c. Both time periods have similarities in orbital configuration regarding weak summer insolation. The difference is that CO2 is much higher today, and this is overpowering the orbital forces which should be driving present-day glaciation.

Milankovitch Cycles of eccentricity, obliquity, and precession (Source)

Though ice ages are ultimately forced by orbital changes, internal climate feedbacks are also vital. When summer solar radiation is low, snow and ice that fell in the previous winter are preserved at high latitudes year-round, and thus are added to the following winter. With this pattern repeating annually for hundreds and thousands of years, Earth starts embarking on a slippery slope to a new ice age. An important impact of increased snow and ice is that an albedo positive feedback loop is created, as light-coloured snow/ice reflects more heat than darker-coloured land, cooling things down just that bit more (see diagram below).

Albedo is greater with snow/ice covered land surface, which means more heat is reflected, thus more snow/ice stays, which reflects more heat etc. A positive feedback loop is formed which has a cooling effect (Source)

Postponing a new ice age might seem like cause for celebration (I'm looking at you, you sun-worshipping, beach-loving, tanned folk). But consider this. Humanity's modification of the atmosphere through anthropogenic carbon dioxide emissions is enough of a planetary-scale forcing to seriously delay the onset of what would've been a natural ice age in Earth's life cycle. The increased albedo needed to shift Earth into a new glacial state cannot and will not happen whilst humans are a dominant geological force. We're tampering with a very sensitive climate system, approaching terra incognita, accompanied by some serious unprecedented consequences. 

Regardless of when human influence of this type upon the planet begun (8000, 200, or 65 years ago), it can be considered unnatural and unhealthy, as it is preventing Earth from undergoing normal cyclical changes. If there's any evidence needed to show that humanity's impact is planetary-scale and significant enough to warrant recognition of the Anthropocene, this is it. This time, it won't be leaves on the line that delays our arrival at the next station 'Ice Age', but something much bigger...

Tzedakis et al's paper is really worth a read, but is perhaps a little heavy reading for those of you unfamiliar with paleoclimatology. Instead, check out Andrew Revkin's 'dotearth' blog post, which nicely summarises the paper and contains some interesting responses from other scientists regarding the findings!

'era today - gone tomorrow?

What is the Anthropocene, you ask?

A simple Oxford Dictionary definition states:

'relating to or denoting the current geological age, viewed as the period during which human activity has been the dominant influence on climate and the environment'

As mentioned in my earlier post, the term Anthropocene was coined in 2000 by Crutzen and Stoermer, based on the rationale that humans are having major growing and lasting impacts on Earth's global systems. Though currently informal, the concept of the Anthropocene represents a paradigm shift in global environmental change research (Mackay 2015, in press*). From contributing to mass species extinctions and tearing down entire forests, to drastically altering the composition of the atmosphere, the question prevails: are humans a significant force of nature?

The general gist is that we are in a geological epoch characterised by human ability to modify Earth systems. A key consequence of formalising the Anthropocene is that it would bring an end to our current interglacial epoch of the last 11,700 years, the Holocene. It is yet to be decided if the Anthropocene will join official geologic time alongside other periods like the Pleistocene Epoch (no, not plasticine!) and the Jurassic Period.

The first meeting of the Anthropocene Working Group (Source)

So who gets to make this decision?

The choice is down to 37 highly regarded scientific brains. These people make up the Anthropocene Working Group (AWG), part of the International Commission on Stratigraphy (ICS) Subcommission on Quaternary Stratigraphy. The group, chaired by Jan Zalasiewicz, have some pretty daunting issues to tackle regarding the Anthropocene: should it be established? When would it start? What hierarchical level should it gain in geologic time? So far there isn't really a consensus, but the decision is due to be made in 2016. So, watch this space!

When did the Anthropocene start - if at all? 

Let us take a look at some of the dates in history when humans made their mark...

~13,800 BP: Megafaunal predation & vegetation change 
(Doughty et al 2010)

• Human predation of mammoths led to an expansion of Birch trees
• Increase in Birch pollen across Siberia & Beringia
• Land-surface albedo changed
• Regional rise in temperature of 1°C

11,000-9,000 BP: Initial plant & animal domestication 

(Smith and Zeder 2013)

• Anthropocene should be coeval with the Holocene
• Plant and animal domestication formed the basis for agricultural expansion
• Humans as 'ultimate niche constructors' 

8,000-5,000 BP: Early Anthropogenic Hypothesis 

(Ruddiman 2003, 2013; Ruddiman and Thomson 2001)

• Gradual increase in methane from wet rice agriculture and livestock
• Increased CO2 from preindustrial forest clearance for agricultural expansion
• Both gas increases evident in Greenland ice cores
• Ruddiman argues this activity prevented natural glaciation

2,000 BP: Anthropogenic soils

(Certini and Scalenghe 2011)

• Anthropogenic soil horizons as golden spikes
• Soils show the best record of early civilisations' impact on the environment
• Ploughing, fertiliser use, contamination etc

AD 1750-1800: The Industrial Revolution

(Crutzen and Stoermer 2000; Crutzen 2002; Steffen et al 2007)

• Exploitation and combustion of fossil fuels - allowed the transition to a high energy society
• Rapid industrialisation
• Coincides with James Watt's steam engine design in 1784
• Haber-Bosch fertiliser process revolutionised food production
• Mass population growth
• Ice cores show increases in CO2 and CH4

AD 1610: Orbis

(Lewis and Maslin 2015)

• Meeting of the Old and New Worlds
• Dip in atmospheric CO2 (of 7-10ppm) detectable in ice cores
• Deaths of ~50 million indigenous Americans due to arrival of Europeans
• Irreversible exchange of species across continents
• Regrowth of forests over abandoned agricultural land

AD 1945, July 16th: Trinity

(Zalasiewicz et al 2015)

• First (tentative) conclusion from the AWG
• Age-based (GSSA) boundary from the first atomic bomb in Alamogordo, New Mexico
• Globally identifiable signature in the chemostratigraphic record
• Historical turning point

The Trinity Nuclear Bomb, conducted by the US Army in 1945. A turning point for human and Earth history? (Source)

AD 1950s: The Great Acceleration

(Steffen et al 2007, 2011, 2015)

• Major expansion in human population, economic growth, resource use and technological advances
• Rapid increases in greenhouse gas (GHG) emissions
• CFCs causing a hole in the ozone layer (though the Montreal Protocol of 1987 mitigated this)
• Various markers within this time period (plastics, aluminium, fertilisers, radionuclides)

AD 1964: Nuclear Testing Fallout Peak

(Lewis and Maslin 2015)

• Atomic weapons testing of the 1960s
• Partial Test Ban Treaty in 1963
• 1964 spike in radionuclide fallout in sediments across the planet

I hope that over the course of my blogging there will be new ideas for when this time should begin, perhaps even complete dismissal of existing ideas, and eventually a consensus formed by the working group. 

And now you can relax. PHEW. If you've read all the way through to this point, and you're still interested, massive congratulations. I want YOU to take part in this debate I'll be directing about the Anthropocene! Comment, vote on the poll, and share your thoughts! 

A dose of pun-tastic Anthropocene banter (Source)

'till next time, folks. Let the debate commence.

*Though currently in press, I've had a read of the personal copy of Mackay's chapter in this upcoming book and it is definitely worth a read! The full reference is: Mackay, A.W. (2015) Anthropocene Epoch. International Encyclopaedia for Social and Behavioural Sciences, 2^ndEdition.

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.