Eocene Telephone

Recently, GG concurred in the observation that myths can persist in the scientific community and added his own story of the “ignorant sheepherder” comment supposedly directed by Whitney at Muir.  Some readers might have said so what, these are innocent little pieces of color commentary independent of the march of science.  So for those skeptics, a more significant example.

A lot of recent work has been done on the Auriferous Gravels.  These papers pretty uniformly assign a middle-late Eocene age to these rocks.  For instance, Cassel et al. (2009, Int. Geol Rev.) said “Middle – late Eocene flora from within the upper half of the sequence are the only dateable material in the prevolcanic gravel (MacGinitie 1941).” A later paper gets a bit more precise (Cassel and Graham, 2011, GSA Bull):

The “Chalk Bluffs flora,” from the auriferous gravels at You Bet Diggings (Fig. 1), has been used to estimate the depositional age. Originally described as Capay stage and interpreted as middle Eocene by MacGinitie (1941), the Chalk Bluffs flora is now considered to be early Eocene (48.6–55.8 Ma; Wing and Greenwood, 1993; Wolfe, 1994; Fricke and Wing, 2004), which is consistent with comparable floral assemblages in other recently dated sections (Meyer, 2003; Retallack et al., 2004; Prothero, 2008).

Hren et al. (2010, Geology) similarly date these rocks: “Plant fossils are classified as Chalk Bluffs Flora after their best-preserved occurrence, and are dated at 52–49 Ma by faunal and floral correlation (MacGinitie, 1941; Wing and Greenwood, 1993).” It would seem that these sediments are pretty firmly dated to 49-52 Ma.

Except that in fact there is no firm floral date for these rocks.

Subtly Siccar

One of the key differences between geology and most other science is that later workers can see the exact same “experiment” as the original workers.  In other fields, replication is the standard; while you cannot see the original experiment, you should be able to reproduce it.  For us in geology, though, we can usually see the exact features interpreted before.

And so in visiting Siccar Point, GG could look at the same rocks that James Hutton saw and used in arguing for the great depth of time needed for geological relationships.  Although Hutton found many unconformities in Scotland, this was the one that has impressed geology more than the others.  The neat thing in visiting is appreciating some of the less obvious characteristics of the place. Here is the classic view found in most geology textbooks:

The “Classic” view of Siccar Point with the angular unconformity between the Late Devonian Old Red Sandstone (dipping gently to the left) and the underlying Silurian turbidites (vertical beds at right). CH Jones July 2015.

Texts often trim away that righthand side and sometimes zoom in even closer to the unconformity. But if you come to visit, that righthand side stands out: those Silurian graywackes are rising up above the unconformity.  Keep that in mind; we’ll come back to it.

People v. Megafauna (Book Review)

One of the more interesting intersections in earth science is at the end of the Pleistocene some 10,000 years ago in North America.  Trying to untangle the climate and human changes at this time is challenging in no small part because you are dealing with experts in archeology, paleontology, and paleoclimate (there is even a small role for solid earth geophysics if you look carefully) as well as cultural clashes over ethnic heritage and, occasionally, legal battles.  It is where GG’s Historical Geology class really starts, so a book really digging in to this material is always welcome.

David Meltzer’s First Peoples in a New World: Colonizing Ice Age Americais a rarity as the author is a working archeologist and the text doesn’t try to gloss over disagreements but instead fleshes out arguments too often presented as disagreements between personalities. Although the book is now five years old and so missing some recent discoveries, by and large this covers the big issues in the original peopling of North America as they still stand today.

When Observations Collide…A Grand Canyon Story

Two stories are out there about the Grand Canyon: one says the canyon is young (cut in the past 5 million years), one says it is old (cut by about 70 million years ago). Why is this?  Fundamentally it is because one group is tied to one observation and another to another. This sort of thing happens in earth science (most intractably in the controversy over the Cretaceous location of British Columbia) and can lead to immense frustration.

Here, the idea that the canyon is young is fairly longstanding and largely based on the absence of detritus from the upper Colorado River in sediments deposited in the vicinity of Lake Mead (the Muddy Creek Formation, should you wish to look it up).  There are workarounds that have been (and continue to be suggested), so let’s not focus on that particular problem now.  There are two pieces of evidence that are close together and whose interpretations are mutually incompatible: a new-fangled radiometric age date and a classic old school geologic outcrop.

A Weighty Problem

One of the key assumptions in applying metamorphic petrology to tectonics (among other fields) is the assumption that the pressure of a metamorphic reaction is the same as the weight of the rock above that reaction.  This makes things reasonably straightforward in interpreting the presence of certain minerals: if you see coesite, for instance, in a rock, you should be at a pressure of 28 kbar (2.8 GPa) or higher (a depth of about 100 km if the average density above is 2850 kg/m³). Discovery of very tiny diamonds and other ultra-high pressure minerals have suggested over the past decade that pieces of continental rock make it to great depths in the earth, far below the deepest continental crust.

Lurking in the shadows for several decades has been the specter that the assumption of equivalent pressures is wrong; that is, the existence of differential stresses at a point means that you can grow minerals that “belong” at a different depth (and also that stress concentrations within a polymineralic material could also affect the minerals that are stable). (Differential stress means that the stress in different orientations is different, unlike in a fluid like water, where the pressure in all orientations is the same. Move a balloon up and down in water and you will see it expand or contract; put it in a vice and its shape will change).  A new paper in Geology (accompanied by a nice overview article) brings this problem to a head by explicitly describing how, in a rock with multiple minerals, application of a differential stress can generate new minerals seemingly requiring a different pressure.

The Wilderness Myth

Sierra reminds us to celebrate the 50th anniversary of the Wilderness Act. While keeping some parts of America free from roads and industrial development is something to celebrate, the concept underpinning this legislation is based on a fictional narrative, which would be amusing if it weren’t clouding the vision for managing these lands. Consider the legislation itself:

“A wilderness, in contrast with those areas where man and his own works dominate the landscape, is hereby recognized as an area where the earth and its community of life are untrammeled by man, where man himself is a visitor who does not remain. An area of wilderness is further defined to mean in this chapter an area of undeveloped Federal land retaining its primeval character and influence, without permanent improvements or human habitation, which is protected and managed so as to preserve its natural conditions and which (1) generally appears to have been affected primarily by the forces of nature, with the imprint of man’s work substantially unnoticeable; (2) has outstanding opportunities for solitude or a primitive and unconfined type of recreation; (3) has at least five thousand acres of land or is of sufficient size as to make practicable its preservation and use in an unimpaired condition; and (4) may also contain ecological, geological, or other features of scientific, educational, scenic, or historical value.” Public Law 88-577, 88th Congress, S. 4, September 3, 1964

Now that part about the imprint of man’s work being unnoticeable? Arguably there is no such place, except perhaps on the very rockiest of crags, where this is true.

Consider, for starters, Yosemite Valley (yes, it isn’t Wilderness, but it stands in nicely for less well known areas that are). When first visited by European Americans, the men of the Mariposa Battalion enjoyed riding their horses through the forest without obstruction. The large meadows and frequent vistas were enjoyed by early visitors to the valley, but those characteristics faded with time.  Why? Because the Ahwahnechee were frequently burning the undergrowth, managing the valley to encourage growth of foods they used and reducing the opportunity for predators to attack them. This behavior was widespread in much of the Americas.  The flora and fauna seen by the first Europeans were shaped by Native American behaviors, which included hunting, setting fire, harvesting (and sowing) various plants.

But this is hardly the most significant impact of humans in North America.  Consider, for instance, the Osage Orange (aka the hedge apple), native to parts of east Texas and a bit of Oklahoma. This charming fruit isn’t eaten by anything (squirrels tear it apart to get at the seeds); the development of such large fruit is usually associated with something that eats the fruit.  Also, in the geologic past this was a widespread plant.  What gives?

Daniel Janzen and Paul Martin proposed in 1982 that this sort of orphaned plant was an evolutionary anachronism, a plant with a specialization lacking modern purpose (think an appendix of the plant world). Why would this happen?  In this case, the idea is that there used to be a big animal that ate the fruit and so distributed the seeds. (Arguably this extends to some animals: pronghorn antelope can run far faster than any plausible predator today; was there a predator in the past that could push them hard?). And looking back in time, we see lots of big animals that could be candidates for a consumer of Osage Oranges.  In fact, there were some 30 or more species of large animal, creatures like mammoths, mastodons, cave bears, camels, saber-toothed cats, dire wolves, etc. that wandered the face of North America. Why are they no longer here?

Almost certainly the answer is the arrival of Homo sapiens. Megafaunae were wiped out in the Americas, Australia, New Zealand, and Oceania almost in lockstep with the arrival of humans.  While the extinction of these animals in North America coincided with the end of the last Ice Age, there wasn’t an equivalent extinction of small animals, nor was there a comparable extinction event at the end of  the numerous previous glacial episodes. Extinction in Australia and New Zealand didn’t coincide with rapid climatic change. So although the means by which humans extinguished these animals remains controversial (some combination of direct predation, competition, collapse of keystone species, changes in ecosystems though the use of fire, and other, more longshot, possibilities like bringing pathogens to areas), the guilt of humanity is very hard to escape.

What this means is that nearly every ecosystem in North America was beheaded some 10,000-13,000 years ago, so they are hardly “untrammeled by man.” These ecosystems have not yet reached any kind of stable equilibrium; they are all carrying the “imprint of man’s work,” both the long term loss of the megafauna and the ongoing impact of human hunting, foraging, and burning. The myth of wilderness arose in part because Europeans had chosen to denigrate the significance of Indian life, partly because many Native populations had been crushed by disease before significant European contact, and partly to make it seem that Americans were taking possession of a vacant landscape. It reached its pinnacle in the mid-20th century in part because direct experience with original Native practices was so distant from American memory (many early Americans were well aware that American Indians had a major impact on the landscape) and in part because the significance of the megafauna extinction was not yet recognized.

Why is recognizing wilderness as a myth significant? Because it influences how we manage these lands.  And make no mistake, we do manage them even when some of the management decisions are to do nothing.  If there is no wilderness in the sense of an untrammeled nature in harmony with itself, what are the goals of having Wilderness?  Are we trying to remake the pre-Columbian America? So should we encourage traditional harvesting, burning, hunting? Are we trying to restore to a pre-human environment? If so, we need to replace those lost species, as has been suggested in the Pleistocene rewilding initiative. Is Wilderness a refuge for the species that survive? We should perhaps then manage these more as wildlife sanctuaries. Is this just a playground for humans to restore themselves away from industrial life?  Then perhaps some of the cosmetic restrictions on management should be lifted. The irony is that current management is, largely, dedicated to making something that never existed before: a natural environment nearly totally beheaded, missing not only the megafauna extinguished some hundred centuries ago, but the humans that replaced them.

Climate Change and Extinction

Its been a rough week on the climate change front.  Work was published online in Science  and Geophysical Research Letters that strongly indicates that the West Antarctic ice sheet has destabilized, meaning that it will likely retreat rapidly over the next century and end up contributing some 1.2m (4 feet) of sea level rise, which qualifies as catastrophic in human terms (especially if you add in other contributions from Greenland and other ice caps). On a related front, a study commissioned by the military has raised the threat posed by climate change to the security of the United States to being a primary threat capable of starting conflicts (as opposed to an earlier 2007 study that indicated that climate change could worsen conflicts).

In this vein, GG would like to offer a piece of information that some might find comforting. While human-caused climate change might well be a threat to civilization, it (at least on its own) might not be quite as horrifying in terms of extinguishing life on Earth as some might contend. One of the great unknowns in humanity’s ongoing experiment in global climate change is just how severely such change will alter the biosphere. Many presume rapid changes are sure to be catastrophic. Bill McKibben (for instance) wrote a book The End of Nature basically saying there is no way that most species can survive. Groups with a similar outlook make apocalyptic claims that most of the world will become a desert.

This book and others’ claims made the Grumpy Geophysicist grumpier. Why? Well, we have examples in the geologic past of some pretty extreme climatic shifts and we simply don’t see quite that extreme a response. Rapid changes in deglaciation near the end of the last Ice Age (the Younger Dryas event) led the climate to flip back from warm to glacial within a decade and somehow the flora and fauna of North America and Europe survived (we’ll argue the megafauna extinction another day; thank you very much for your patience).

This isn’t to poo-poo impacts of rapid climate changes too much. Major extinction events at the end of the Paleocene and end of the Eocene were both marked (and almost certainly caused by) dramatic shifts in the climate. It is just that in neither case was the land left barren and uninhabitable (and the Eocene was a lot warmer than today, too, so somebody out there can handle hot tropics–in fact there was diversification of flora in the tropics during the rapid warming at the end of the Paleocene).

Well, say climate catastrophists, those events were slower (other than the end of the Ice Age thing, which appears to be more regional to the northern hemisphere). And indeed it appears that the changes at the end of the Paleocene (going into the Paleocene Eocene Thermal Maximum or PETM), which is arguably the best natural experiment in rapid climate change, took about a thousand years. At least, that was the story until some recent work.

Our estimates of the rapidity of the change at the end of the Paleocene (or start of the PETM) has largely been based on deep sea records. The problem there is twofold. One is that sedimentation rates on the deep sea floor are low: a thousand years might be less than a centimeter of rock. The other is that many of the deep sea indicators are reflective of the ocean as a whole, but the ocean takes nearly a thousand years to reach equilibrium with the atmosphere. So two researchers, James Wright and Morgan Schaller at Rutgers looked at some shallow water sediments from this time preserved in southern New Jersey. They noticed that there are rhythmic layers that, they argued, were annual varves created as seasonal streamflows flushed sediment into the shallow ocean. They see the changes in temperature associated with the beginning of the PETM. And it happens within 13 years.

This is amazing on a few counts (GG is not easily amazed). First, to have a record with such fidelity that you could look not only at annual averages but look at seasonal variations [other such records are growth variations in organisms, but these are tougher to tie to a particular event]. Second, that this global change could occur in 13 years or less (it could be less because it still takes some time for even the shallow water to equilibrate).

If these authors are correct, the truly dramatic changes associated with the initiation of the PETM (estimated release of 3000 gigatons of carbon–or more–in just over a decade or less) outdo modern releases of carbon (~30 gigatons/year). We have lots of good reasons to suspect that extinction rates are tied to the rate of change in the environment; if the PETM was really this quick and only produced the level of extinction seen, we might expect that anthropogenic climate change, especially if we limit the rate to something like modern rates, might not (in and of itself) be a catastrophic “sixth extinction.”

Of course this study has invited skepticism; in some ways, the biggest surprise is that these criticisms don’t look particularly fatal.  Arguably the largest potential concession might be that instead of 13 years, the record might be more like a couple hundred years if the varves are really from decadal (and not annual) variations.  This is still pretty fast and comparable to modern fluxes of carbon. This will bear watching: the PETM is the best template we have in the geologic record for what massive infusions of carbon into the atmosphere will do.

Now before you happily go gassing up your Hummer before taking your private jet for a spin around the neighborhood, do keep in mind there were some notable extinctions of some mammals in the PETM and a big extinction of plankton in the oceans. Also, this time out there are a lot of other factors in play.  Humans already caused an extinction of megafauna without needing climate change, and the current extinction event sweeping the amphibian world looks to be enabled by human trade and agriculture. So while anthropogenic climate change itself might not create a major mass extinction, toss in all the other things humans are doing and the prospect for a lot of species isn’t too bright.

Climate change from a deep time viewpoint

Recently the government released a national climate assessment and not long before that the IPCC released their most recent major report. So it is time for all those who want to continue doing what they are doing to deny that any of this is correct. So rather than hammer on the same old talking points (which makes GG even grumpier), let’s look at this slightly differently.

It is easy to show that carbon dioxide has been increasing in the atmosphere for more than 50 years, and it is also pretty easy to show that this is from burning fossil fuels. This isn’t usually in dispute, but if you want, check into the changes in the isotopic composition of atmospheric carbon dioxide: it is rapidly growing richer in light carbon, which is a signal of fossil fuels.

Anyways, it is typically at this point where disagreements emerge. The climate community is very proud of their models and points to them as showing what will happen if CO₂ levels continue to increase. Now these models represent a huge amount of work, but GG feels sometimes they don’t understand why models aren’t too convincing outside their community. Perhaps they don’t notice the occasional epic fail in a weather forecast, the inability to forecast a La Niña or El Niño event reliably or the continued uncertainty around some even longer term oscillations in the atmosphere that defy these models. And GG recalls that less than 15 years ago these models were predicting increased ice cover in Greenland (that prediction certainly went south). And there has been a long-standing problem with explaining the earth’s climate back in the times when there were no glaciers (in the Cretaceous, say, or Eocene) that suggest there could be stuff missing in climate models [and yes, GG is aware of some recent papers that maybe have solved this and maybe we’ll discuss later, but this still needs to be sorted out]. So GG understands a distrust of model predictions. But you know what? Models can be wrong in both directions: they might be underpredicting problems, too.

Now the basic objection raised is that the models are missing a large negative feedback, which means that as carbon dioxide increases, something else changes too that makes things cooler. The most popular suggestion is that water vapor will rescue us by generating more clouds or fewer clouds (depending on the place) and balance things out. This line of argument rapidly descends into arguments over coefficients in the models that seem so esoteric that lots of folks think this is like angels dancing on the heads of pins and so they tune out. Ugh.

Being of a geological mindset, GG suggests looking at the Earth’s history instead. We have lots of ways of estimating temperature in the past and quite a few for getting a handle on carbon dioxide in the atmosphere. Looking in ice cores we see the warm interglacials were accompanied by higher levels of carbon dioxide and major glaciations low levels. As more astute readers might know, there is an interesting timing issue in the details that is caused by the initial forcing of that climate change being changes in the earth’s orbit, but let’s not sweat that and instead look even farther back. We can look at the end of the Paleocene and find a rather rapid increase in carbon dioxide in the atmosphere and ocean. At the same time we see a massive increase in temperatures (something like 5 degrees C or 9 degrees F in ocean temperatures). Seems like the magic negative feedback failed to rescue the planet back then.

Don’t like those proxies? How about something simpler: the presence of continental glaciers. These leave really easily identified remains in the rock record. We look back before 35 million years ago and we have to go all the way back to the late Paleozoic, some 280 million years ago, to find big glaciers—and they were really big. What was carbon dioxide back then? Really low any way you slice it, but in some ways the simplest thing to look at is what is in the rocks early in the glacial period and just before. What you find are massive coal deposits. In fact, most of the coal we’ve burned and then lots more comes from this time period. The burial of all this coal—the largest coal deposits in Earth’s history—represents a massive reduction in carbon dioxide in the atmosphere. And yet  those negative feedbacks from increasing CO₂  just don’t seem to show up. Pretty much in every way you look at it, increasing carbon dioxide makes the world warmer.

Now to be fair, there is a major negative feedback out there. Increasing carbon dioxide will lead to increased chemical weathering of rock. This takes carbon dioxide and combines it with calcium or magnesium in rocks to create limestones and dolomites in the oceans. The only problem is that this is a very slow process taking tens of thousands of years to recover carbon dioxide from the atmosphere. GG can’t speak for you, but he doesn’t think it wise to wait for this process to clean up our mess.