Thursday, January 31, 2013

Explain the Universe. Give Two Examples

was one of the questions Eli and the bunnies wrestled with as a possible stumper on our comprehensive exams.  AGU has another:  Define the Anthropocene

But it has to be done in terms of what the cyanobacteria, or whatever succeeds humans, will be able to spot in 100K years or more.  Paul Crutzen introduced the term to describe an epoch in which humans dominate changes to the Earth, but for the geologists (and they have the last word in naming epochs) it has to be done in terms of traces in the solid Earth at the stratigraphic level.

There is a working group and there was a symposium on this issue at the 2012 AGU and an article in EOS Jan 22.  Anthony Barnosky from UC Berkeley pointed to

some applicable biostratigraphic evidence for the placement of the Anthropocene boundary could include biostratographic zones for taxa lineage, assemblage, and abundance. He also noted that the road system could be a useful boundary layer. Barnosky said that roads, which often include several layers of geologically resistant human-derived strata, “are probably going to be a more significant boundary layer in the long run than the K-T boundary clay.” Defining the Anthropocene as a formal epoch “clearly is already supportable by paleontological principles you would apply for other epochs,” and biostratigraphy argues for a Holocene-
Anthropocene boundary near 1950, he noted.
IEHO, some of the folks are too hung up on assigning an exact date.  You can't do that for other Epochs.

What say thee.  The Subcommission of Quaternary Stratigraphy is interested in hearing.

19 comments:

Brian said...

Cyanobacteriogeologists of the distant future will not acknowledge a Holocene - they'll say the Anthropocene started at the beginning of this interglacial, and track it to the loss of the large Pleistocene mammals. Or possibly even much earlier and point to the loss of the Australian megafauna 40-50kya as the starting point.

Tom Curtis said...

I'll have a crack at this.

The first limit is resolution. At in 100 k years, time resolution in dating of events is unlikely to be accurate to closer than plus or minus 500 years; and may be significantly less accurate than that. Ergo, dates that make sharp delineations between years, or decades are out. That sort of resolution is very good geologically, but cannot distinguish between, for instance, the MWP and the current era. It does, however, allow distinction between the commencement of the Holocene and the commencement of the Anthropocene (something it probably will not be possible to do several million years in the future).

Within that constraint, a central estimate of about 1750 seems appropriate. That period sees a massive upsurge in a number of geologically persistent markers, including:

a) A new, massive wave of extinctions which will be very clear in the fossil record;

b) A sudden, and massive drop in biodiversity as mainly old world species colonize the globe;

c) A distinguishable increase in sedimentation rates in off shore silts due to erosion from farming;

d) Probable global markers in sediments from polution (similar to the Iridium layer at the K-T boundary);

All of the above will be wide spread, and evident in nearly all appropriate formations.

On top of that there will be very localized evidence from the remains of cities, mines, railways, and as mentioned above, roads.

jyyh said...

to state the obvious, massive disappearance of near-surface carbonaceous strata from the continents and their margins thats been aparent since the 1970s should be visible for at least the to the formation of next supercontinent.

Peter said...

I've seen it suggested that the most obvious marker will be the isotopes left by atmospheric testing in the 1950's, but I'm not enough of a geologist to say whether that's realistic.

Localised archaeological evidence (buildings, roads etc) seems much less likely to be useful

Russell Seitz said...

Define the Athropocene?

That started as soon as Crutzen coined the term --

By their rocks shall ye know them.

Anonymous said...

If an anthropocene falls in the stratigraphic record and there is no one there to view it, does it make a mark?

"The Carburniferous Period"

-- by Horatio Algeranon

Humans ruled
And fossils fueled
During the Carburniferous.

Climate warmed
And weather stormed
But we could not deliver us.

Fossils returned
For no one learned
And time will not forgive for us.

Monty said...

'Anthropogene' was coined long before Crutzen ASAIK. I can find reference to Gerasimov in 1979 to describe what we would now call 'Anthropocene'.

Russell Seitz said...

I first met Gennadi and Paul at the same conference in '84, and there was no mention of it at that time . If it's a Cyrillic neologism, I don't recall it making it over the Latin alphabet divide - Crutzen gets credit for taking it public.

Anonymous said...

What about the remains of all that tetraethyllead we used as a fuel additive for a good half-century? Isn't there still a lot of that in the soil?

bill said...

I went to a presentation at Womad Earth Station in 2011 where Professor Mike Sandiford addressed this very issue in a talk entitled, appropriately enough,'Welcome To The ‘Anthropocene’ : Humans As Geological Agents'.

Now, this is all IIRC, but he mentioned the blanket of Tetraethyll lead across the globe as a clear marker of the Anthropocene - and added the information that most of it will be discovered to have come from Broken Hill, a town in New South Wales so much closer to Adelaide, where I live, than Sydney that it's seen as an honorary part of South Australia.

(Bunnies may have heard of a little outfit called BHP.)

One of his other points is that humans are far and away the most erosive force on the planet, shifting way more dirt than rain, wind, rivers, glaciers etc. could hope to.

I was gobsmacked by a lot of the information he gave - particularly when relating the amount of energy going to power the state of Victoria's air-conditioner-driven electricity peak consumption on a hot summer afternoon relative to the amount of energy involved in shifting the continents around. I still think I must have misheard something, or some small part of my brain fell out, but he says human energy use is 0.33 of plate tectonics! And on pace to overtake it by 2060...

I really recommend reading Sandiford's piece at the Conversation, linked above. (Bunnies will be astonished that the comment thread is immediately hijacked by Doug Cotton.)

EliRabett said...

Bill, do not underestimate the large amount of lead distributed in the two world wars and numerous little ones. Machine guns and airplanes contributed to the rate of fire.

Steve Bloom said...

That's brilliant, Horatio, and thanks.

Re placement of the Anthropocene, I propose:

The geologic period following the Holocene, together constituting the first two periods of the Inhofian (aka the early Cautionary).

coby said...

I second Eli's comment about an exact date. Geologically speaking "now" is about as accurate as you could want, for any value of "now" any reader of this comment may care to assign at any time it will ever be read. (unless I really am the Messiah as I have long suspected and the coming New New Testament that will eventually be written about me is eventually archived in a truly "permanent" medium that will be recovered some million+ years hence and read by some future archeologist of some future species. To that future being I say "Hey! How's it going, dude? ("Dude" is an example of an inappropriate use of a coloquial expression of casual friendship, in case you are wondering) Looking for the start of the Anthropocene? How about using some 8000 years after the start of this, the last interglacial in this current ice age?")

Their eventual reply is somewhat difficult to predict.....

Russell Seitz said...

Since those two great Holocene inventions, fire and pointy sticks, came on to the scene , anthropoids have alterered the albedo or permeability of about half the land surface of the earth.

Since the age of inadvertent geoengineering antedates the Anthropocene by the better part of a million years, the present Committee may have less to sort out than sucessors tasked with stratifying the successive impact signatures of regional or global changes precipitated by species preceding H. sap.



Welcome to the Late Austrolopithicene, AKA the Homo floresiensis Fluorescence

Anonymous said...

Bill:

"I was gobsmacked by a lot of the information he gave - particularly when relating the amount of energy going to power the state of Victoria's air-conditioner-driven electricity peak consumption on a hot summer afternoon relative to the amount of energy involved in shifting the continents around. I still think I must have misheard something, or some small part of my brain fell out, but he says human energy use is 0.33 of plate tectonics! And on pace to overtake it by 2060..."

This echoes a subject that's been on my mind for a few days.

There's an ecological principle that about 10% of photosynthetically-captured energy passes from one trophic level to the next hight one. So of a million joules of shiney sunshine captured by lettuce, ~ a hundred thousand will fuel caterpillars, ten thousand will fuel chickens, and one thousand will fuel humans... with any degree of sustainability. Of course it's more complicated than that (including the presence of more trophic levels than I describe) but you get the general idea.

Consider that humans are currently sucking about 550 exajoules per annum:

http://www.theoildrum.com/node/8936

an that annual photosynthetic energy capture is apparently around ten times this value:

http://www.fao.org/docrep/w7241e/w7241e05.htm

For a species that exists at the apex of the trophic pyramid to co-opt such a disproportionate amount of energy is simply thermodynamically unstable. This is not to say that the energy must comes from the biosphere, now or in the future (obviously we're sucking moat of it from the last three hundred millions years or so of photosynthetic banking), but its expenditure during human activity is inextricably linked to the overall entropic state of the biosphere.

And as I said recently on another Rabbet Run thread, thermodynamics is a bitch. There's simply no way that a huge proportion of the sand in the sandpit can be stacked grain upon grain upon grain in one corner. Other civilisations found this out in the past: our turn is coming, with much of the thermodynamic debt to be paid by the agency of extinction - if not of our species, then by many others, both floral and faunal.

Thermodynamics/entropy imply an asymptote that defines maximum sustainable human energy use, no matt erhte source of the energy. Overdraw, and the excess will be paid with high interest.

And the bitch always gets her money back.

It's a lesson that too few understand, even amongst the scientific fraternity.


Bernard J.

Russell Seitz said...

And now for an inspirational message from Willis Eschenbach:

Chance the widdershins steps of the tarantella, lift the ancient curses and look under them for old coins and lost loves and dust bunnies with a vest and a gold pocketwatch, opt for an immediate increase in the uncertainty levels, stay away from the world of adrenalin deficit spending, hold your dearest warm under your heart while you dare the icy seas of life,

EliRabett said...

The dust bunnies are the ones to watch out for. Do you know how much global warming aerosols are responsible for?

Russell Seitz said...

No, but I hope the gold watch is waterproof and boiling stock resistant.

Robert Grumbine said...

I recall seeing an EOS article by Cesar Emiliani some years before Paul Crutzen's mention of the idea. Partly Emiliani was arguing for a zero year of about 10000 BC in current notation. But the basis included substantial reference to 'anthropocene' thinking.

Anyhow, easily found (in geological terms) evidence will include
* The Great Unconformity (farming has uprooted and blended the upper meters of a large fraction of the planet; add in slash and burn agriculture leaving an easy 'wild'fire signiature starting ca. 10,000 years ago)

* The Great Extinction (which will be distinguishable in, e.g. the loss of all large mammals from North America ca. 10000 years ago, plus major losses in amphibians and others in more recent times)

* The Atomic Age (above-ground nuclear testing has produced so many long-lived isotopes, and sent them so far around the world, that it'll be easy to detect for millions of years. One impactor was able to fling enough iridium around the world that we could find it easily 63 million years later. And that's for a trace element -- not afterwork of something purposefully enriched in U235.)

* Ice cores + trace metals (we can detect the onset of the Iron Age in the polar caps for the trace metals from refining. Current usage is trivial, comparatively, to see). (ok, have to assume that the ice sheets survive present activities, but if AA does, then no problem. A-Bomb debris is trivial at that range.)

* Dam deposits. (Even if the concrete + rebar of the Hoover Dam (e.g.) is undetectable, the rapid construction of a sediment wedge in a place where one would not be expected will be tell-tale. Aswan high dam, three gorges, .... There are plenty of dams that are building sediment wedges of some size. Thorough geological exploration will show them up.)

* Ocean C13 excursion (The fossil fuel carbon signature is depleted in 13C, and such excursions are easy to observe in the geologic record. One is at the KT boundary, 63 million years ago. Ours is already, I think, larger than that.)

* Ice Bubble CO2 levels (we're already far above anything observed in the past 800 ky, and have been for long enough that even an averaging process will show it.)


... and, no doubt, several more.

If the present layers of Antarctica survive 100 ky, then our future geologist should be easily able to get notice and date our activities to 1950 give or take 1000 years. For reasons related to those above 'BP' means 'Before Present', which is defined in those areas as 1950. So I'll go with that too.