K-Pg Mass Extinction: Asteroid Impact Opponents Are Not Giving Up

Just weeks after a mega-paper in Science concluded that the Chicxulub asteroid impact was responsible for the late Cretaceous mass extinction, opponents of that theory are at it again.

Dr. Michael Prauss has submitting some work on the Brazos section in Texas which according to him shows that the Chixculub impact was not the sole cause of the extinction.

The basic argument of the opponents has been:

In stratigraphic sections spanning the late Cretaceous to Paleogene north of the impact site in parts of Mexico, Texas and New Mexico, there is sediment between the impact layer and the geochemically and micro-paleontologically defined Cretaceous-Paleogene boundary. This sediment accumulated gradually according to them. They estimate that the impact occurred a good 300,000 years before the K-Pg boundary crisis and thus the asteroid impact could not have been the sole cause of the mass extinction.

Opposing this view, the proponents of the impact theory say that this sediment is an event deposit which formed within hours to days of the impact and therefore the impact layer is the K-Pg boundary.

In this recent study published in Palaeogeography, Palaeoclimatology, Palaeoecology (I haven't read the paper -behind pay-wall) and described in Science Daily Dr.Prauss  has shown that in the sediment between the impact layer (he calls it ED for event deposit) and the K-Pg boundary there is a gradual increase to peak abundance in trilete spores. This he interprets as indicative of recolonization of damaged landscapes possibly after the asteroid impact by pioneering fern species but well before the Paleogene.

And below the ED in the entire studied section spanning upper Maastrichtian to lower Danian there seems to be signatures of long term sea-level fluctuations and also fluctuations in the oxygen and carbon isotopes matched by fluctuations in the types of dinocyst - a type of marine protist- assemblages.

He concludes that the data shows there to be a significant time span between the impact layer and the K-Pg boundary layer (as judged by the gradual increase in trilete spores) and that the K-Pg boundary was preceded by a long period of high frequency environmental changes and ecosystem degradation going back to a time even before the asteroid impact, a pattern inconsistent with a single catastrophic cause for the mass extinction.

Its really remarkable how two teams can come to conclusions which are such polar opposites. Supporters of the meteorite impact theory have interpreted the said sediment as an event deposit. Their opponents have read long term sea-level changes in the same section and have included the sediment in a sequence stratigraphy framework! There seemingly cannot be a reconciliation of these views. One reading of the data is completely wrong. Both sides will vociferously state that they are going strictly by the evidence but you just wonder how much of an influence does allegiance to a pet theory have on your reading of the data.

Earlier the opponents of the impact theory (Gerta Keller and her team) had based a lot of their conclusions on the presence of sedimentological features suggesting gradual deposition in a quiet environment and on the presence of late Cretaceous foraminifera in the sediment above the impact layer.

This line of reasoning was rejected by the supporters of the impact theory on the grounds that the foraminifera were not really foraminifera but recrystallized dolomite which looked like foraminifera! Alternatively some suggested that the presence of late Cretaceous foraminifera was due to the mixing of materials of different ages during the violent reworking and redeposition of sediment just after the asteroid impact.

All this is very confusing. The evidence collected in favor of the asteroid impact theory is massive. On the other hand it will be interesting to see how supporters of the impact theory explain the apparent preservation of correlated sedimentological, geochemical and palynological trends signifying long term change in environmental conditions.

And that pattern of gradual increase in spore content should not be preserved in a reworked event deposit.

Papers On Indian Quaternary: Paleoclimate, Geoarchaeology And Such..

I came across this treasure trove of articles on the Indian Quaternary. They are from the research group based at Deccan College, a well known centre for Quaternary research in Pune, western India.

The page has been created by Sheila Mishra, faculty at Deccan College. The papers represent a range of topics from paleoclimate, Paleolithic tool and material record of early humans, fluvial geomorphology and insights into neotectonics, Quaternary stratigraphy based on tuff chronology and so on..

The list is long but in a sense restrictive since it represents the work of one group. Geographically too it is biased towards the western and north western parts of the country..the states of Maharashtra and Rajasthan feature prominently.

Still it is a treasure trove, since the journals in which these papers have been published are either behind pay-walls or don't have an online presence.

There are plenty of topics here to explore if you are into Quaternary geology and geo-archaeology.

I am left wondering though whether authors can just scan their publications and allow free access to them without the journal objecting to such practices. I've managed to download papers not just from this website but from other faculty websites in India, papers which are simultaneously behind pay-walls at the journal websites.

Its possible that some journals police this better than others and I'm sure I am not the only one making use of this free access to the author's copy.

Beats paying $ 30/- or so for one download.

Strain Is Accumulating On Istanbul

Here is a good example of how geoscientists are creeping towards a better understanding of earthquakes by monitoring and estimating slip rates along major faults which then are used to estimate locations and likely magnitudes of future earthquakes.

The north Anatolian fault near Istanbul, Turkey has been accumulating strain since the last big one in 1766. Measurements and model estimates of slip rates along the main Marmara fault indicates that the slip rates are variable along the length of the fault.

The supplementary information to the paper is open access and the figure below shows estimated slip rates along the Marmara fault which is beneath the Mediterranean sea bed for long portions of its length.

This might mean scientists think that the building strain would eventually be released not as one big earthquake but several smaller ones as portions of the fault fail at different times and with differing intensities.

That's not to say Istanbul can breathe easy.

Continuing with my previous theme of how well prepared different countries are to face earthquakes and their aftermath, Istanbul scores lower than Chile in the quality of its building structures.

Andrew C. Revkin of Dot Earth interviews Turkish builder Ali Ağaoğlu who admitted that most developers in Turkey have in the past used inappropriate materials for constructing buildings. Since 2000 though all new construction according to him is of good quality but that still leaves about 70 percent of settlements vulnerable to a major earthquake.

How should the city respond? The interview reveals a tension between those that want government help in retrofitting old buildings against private developers who want the buildings razed and new ones built.

Tracing Geology Back To Copernicus

Walter Alvarez and Henrique Leitao argue in a paper in Geology that the geological revolution began not with James Hutton and other geologists in the 18th century but centuries earlier with Copernicus:

We offer a new interpretation of the Copernican Revolution, aimed at generating interest among geologists in the history of their own science. We stress that it is not intended as an in-depth study in the history of science, but as an exploration of a novel idea that may subsequently merit that kind of attention from historians of science. Those scholars of course know that considerations of the Earth played an important role in the Copernican Revolution (Goldstein, 1972); our new point is that that revolution can be viewed as part of the history of geology. We thus hope to raise the awareness of geologists about a major episode in the history of science that can be seen as a geological development, and of the critical role that Earth science has played in the rise of the modern scientific world system.

Far from viewing the Copernican revolution as one that demoted the earth from its original place at the center of the universe to just another planet, the authors suggest that recognizing the earth as just another planet paved the way for understanding universal laws.

...we realize that recognizing Earth as a planet was a precondition for understanding the universe. When that recognition destroyed the Aristotelian view that Earth is fundamentally different from celestial bodies, the Earth could become a laboratory for studying the universe. For example, had Newton’s worldview not been shaped by decades of challenges to Aristotle, he would probably never have had the idea (symbolized by the perhaps apocryphal story of the apple) that the same force of gravity that acts on Earth was keeping the planets in orbit around the Sun.

In an article in Discovery news Alvarez makes the point that geology has been traditionally neglected or at least placed on a lower pedestal than physics and chemistry at the school level and that a lack of understanding of the history of geology may be partly responsible for this. He and Eldredge Moore press the case for making geology an important component of school science syllabus.

Self Domestication Of Humans And Symbolic Language

There are topics I like to read about and I think I am understanding the subject matter as I read along. But if asked to explain that to someone else.. I would probably draw a blank.

The evolution of language is a fascinating topic and on NPR's Cosmos and Culture blog language experts Terrence Deacon and Ursula Goodenough write a post on the evolution of symbolic language in humans:

The world of symbols is an artificial niche, its ecology radically different from the biological niche we also occupy. In the same way that beaver dam-building has created an aquatic niche to which beaver bodies and behavior have adapted over their evolutionary history, our cognitive capacities have adapted to our self-constructed symbolic niche.

..and this very interesting take on how domestication or rather establishment of a particular social and cultural niche in early human societies may have prodded the evolution of complex language:

Recent investigations of birdsong offer some clues in thinking about language evolution.

As expanded in an earlier blog, a comparative study of a recently domesticated bird and its feral cousin revealed that the domesticated lineage is a far more facile song-learner, with a much more complex and flexible song, despite the fact that the domesticated bird was bred for plumage coloration, not singing.

That this behavioral and neural complexity arose spontaneously was surprising given the common assumption that song complexity evolves under the influence of intense sexual selection, which was not operant under the breeding regime. One intriguing interpretation is that the relaxation of natural and sexual selection on singing was in fact responsible for its complexification. With song becoming irrelevant to species identification, territorial defense, mate attraction, predator avoidance, and so on, degrading mutations and existing deleterious alleles affecting the specification of the stereotypic song would not have been weeded out, the result being a reduction in the innate biases controlling song production. With specification of song structure no longer strictly controlled by the primary forebrain motor center, auditory experience, social context, learning biases, and attentional factors could all begin to influence singing, the result being that the domestic song became more variable, more complicated, and more influenced by social experience.

Relaxation of selection may have led to phenotypic plasticity - in this case an increased repertoire of behavioral /audio responses - being tolerated and eventually the genetic basis for this increased range was positively selected for over evolutionary time and became an adaptive feature.  I think this is called genetic assimilation or the Waddington effect.

I may be wrong about this being an example of genetic assimilation... but...in any case the article is worth reading.

I Hereby Bequeath You My Dog

Nicholas Wade writes about the possible locale of the earliest dog domestication and its impact on human societies:

Dog domestication and human settlement occurred at the same time, some 15,000 years ago, raising the possibility that dogs may have had a complex impact on the structure of human society. Dogs could have been the sentries that let hunter gatherers settle without fear of surprise attack. They may also have been the first major item of inherited wealth, preceding cattle, and so could have laid the foundations for the gradations of wealth and social hierarchy that differentiated settled groups from the egalitarianism of their hunter-gatherer predecessors. Notions of inheritance and ownership, Dr. Driscoll said, may have been prompted by the first dogs to permeate human society, laying an unexpected track from wolf to wealth.

Figure below (see link for explanation) depicts the genetic relationships between dog breeds to wolves.

Close proximity to animals and its impact on both biological and cultural evolution of humans is increasingly being appreciated and studied. In a sense domestication goes both ways...e.g. was inter-tribe /clan/family violence moderated by the presence of dogs protecting settlements?

Here is a link to the paper in Nature and if you want to listen to one of the lead scientists Robert K. Wayne I dug out this old talk on NPR on dog evolution and domestication. Its worth a listen.

Darwin On Earthquakes

Just a follow up to my previous post on Darwin's observations of the Chilean earthquake.

I came across this passage from the Voyage of the Beagle:

A bad earthquake at once destroys the oldest associations: the world, the very emblem of all that is solid, has moved beneath our feet like a crust over a fluid;—one second of time has conveyed to the mind a strange idea of insecurity, which hours of reflection would never have created.

His prose occasionally leaves a feeling of Victorian tediousness to modern readers but this is beautifully expressed. He scores high on the poignancy scale.

A Geological Ode To Charles Darwin

And so really, it's just a scandal that the biologists have absconded with Darwin's memories.....He's ours. He's a geologist, and we're filing a class action suit..

Geophysicist Ross Stein of the USGS makes a good case in a discussion which turns into a tribute on Science Friday that Charles Darwin had foundational influences not just in biology but in geology as well.

On February 20th 1835 Darwin was ashore in Valdivia on the Chilean coast when a great earthquake struck.

From The Voyage of the Beagle: [page] 369 Feb. 1835. GREAT EARTHQUAKE.

The day has been memorable in the annals of Valdivia, for the most severe earthquake experienced by the oldest inhabitant. I happened to be on shore, and was lying down in the wood to rest myself. It came on suddenly, and lasted two minutes;

On March 4th the H.M.S. Beagle sailed into Concepcion port and Darwin and his crew witnessed a town devastated. He along with Capt. Fitzroy wrote about the damages and human suffering in their diaries.

But soon the scientist in Darwin took over and he made several insightful geological observations and reflections on vertical movements of the crust during earthquakes and associated volcanic and magmatic activity and their link to the formation of mountains chains:

[page] 379 March 1835. VOLCANIC PHENOMENA.

It is almost certain, from the altered soundings, together with the circumstance of the bottom of the bay near Penco, consisting of hard stone, that there has been an uplifting to the amount of four fathoms, since the famous convulsion of 1751. With this additional instance fresh before us, we may assume as probable, according to the principles laid down by Mr. Lyell,* other small successive elevations, and may fearlessly maintain that the problem of the raised shells,† recorded by Ulloa, is explained.

And then he astutely links the earthquake clusters with the coincident volcanic activity into an explanation for the formation of mountain chains:

[page] 380 CONCEPCION. March, 1835.

The elevation of the land to the amount of some feet during these earthquakes, appears to be a paroxysmal movement, in a series of lesser and even insensible steps, by which the whole west coast of South America has been raised above the level of the sea. In the same manner, the most violent explosion from any volcano is merely one in a series of lesser eruptions: and we have seen that both these phenomena, which are in so many ways related, are parts of one common action, only modified by local circumstances. With respect to the cause of the paroxysmal convulsion in particular portions of the great area which is simultaneously affected, it can be shown to be extremely probable, that it is owing to the giving way of the superincumbent strata, (and this giving way probably is a consequence of the tension from the general elevation) and their interjection by fluid rock—one step in the formation of a mountain chain. On this view we are led to conclude, that the unstratified mass forming the axis of any mountain, has been pumped in when in a fluid state, by as many separate strokes as there were earthquakes.

He saw raised beaches and altered depth soundings...conclusion.? ..the crust moved vertically during earthquakes...this must have happened many times in the past as well...applying Charles Lyell's principle of uniformitarianism...

..so..along with injections of magma, such episodic movements of the crust will eventually form high mountain chains like the Andes... and as Ross Stein elaborates...since these processes occur only episodically, it must be taking millions of years for mountains to form...therefore the earth must be really really old.

aside from these fundamental insights he explains the origin of batholiths oriented along the axis of mountains:

On this view we are led to conclude, that the unstratified mass forming the axis of any mountain, has been pumped in when in a fluid state, by as many separate strokes as there were earthquakes.

 
Not bad coming from one of the foundational figures of..modern biology.

What really struck me was the striking contrast in his descriptions of the gradual process of mountain building as against the gradual process of organic evolution. For mountain building he envisioned violent episodic events..the convulsions and paroxysmal earth movements that raised the crust in leaps and bounds and those new elevations gradually accumulated to raise the crust to great heights. Earthquakes were disruptive events and in between .... nothing happened...it was long periods of boredom followed by short periods of terror. Mountains formed through gradual but discontinuous processes.
 
Contrast this with his mechanism of biological evolution which also consisted of gradual change but one of a different nature. It proceeded through tiny changes which accumulated continuously..generation after generation. The rate of change may not necessarily be the same but change was continuous. He positively rejected the idea of disruptive changes or discontinuities when it came to explaining the origin of organic form. Traits did not come into existence through sudden leaps. His mechanism of natural selection acting on slight variations among individuals in a population demanded that descendants would differ only by very tiny increments from their immediate ancestors. Organic evolution therefore had to be gradual and continuous.

Ross Stein is right. Darwin was more than a competent geologist and he thought very deeply about geology...he had to.. since the abrupt appearance of new species and groups in the fossil record was a headache for him. This he explained mostly on the geological grounds of the presence of massive discontinuities in the preservation of sediments and fossils.

But he also saw a much more fundamental difference between geological processes and organic evolution and the difference was one of uniqueness.

For him, geological processes were part of the grand recycling of the planet. Magma rose up and solidified as rock. That rock over eons got weathered and the resulting sediment got buried and remelted into magma, starting another cycle of rock formation. Sea level rose and fell cyclically depositing sediment.

Biological evolution on the other hand produced unique features. The evolution of any new trait or species was a phenomenon without precedent and without anticipation of being repeated in the future. A particular novelty, a particular evolutionary trend or pattern in a lineage evolved through a contingent sequence of events only once in the history of life.

His most famous book - The Origin of Species - reflects these thoughts as it ends:

"There is grandeur in this view of life, with its several powers, having been breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Geopoetry Over At The Yucca Mountain

Yucca mountain, Nevada - the plan to use it as a long term storage of America's nuclear waste has been indefinitely nixed. Creative writing professor John D'Agata has written a book about it called About a Mountain and he reads a passage from it on Talk Of The Nation:

Beyond the trees, the haze of heat listed over desert. Fifty wavy miles, then highway strip, then miles. Then black encrusted ridges bumping silently from earth. So, Josh said, what do you think? Of what, I asked? Of Yucca, he said. Where? Straight ahead. Where? That low range. Really, I asked?

Yucca Mountain isn't pretty. And it also isn't large. From far away, the mountains just a squat bulge in the middle of the desert, essentially just debris from a bigger, stronger mountain that erupted millions of years ago and hurled its broken pieces into piles across the earth. The Shoshone say that Yucca is the carcass of a snake, a giant desert creature that was trying to find a drink collapsed there in exhaustion, rotted as it died. Better a cruel truth, Edward Abbey once wrote, than a comfortable delusion.

So we climbed the mountain higher and the spruce begin to wither and the bristlecones to gather, and the pitch of trail sharpened, and the edge of ridge straightened, and the soil whisked off limestone sheets and loosened them to shingles. Joshua pulled my mother quickly in front of him and said, watch it here, the path is narrow, as the path ahead began to fade and then it disappeared.

A proposed nuclear waste site can also inspire...geo-lit?

Chile, Haiti, India....And Earthquake Preparedness

On NPR's Talk of the Nation (March 1) guests discuss earthquake preparedness and why the Haitian earthquake caused much more damage than the Chilean one despite the Chilean earthquake being more powerful.

Geology is part of the answer. The Haitian earthquake occurred closer to population centers and was shallower. So a very large population was exposed to violent ground shaking. In Chile the earthquake was farther away from large population centers with the most violent ground motion taking place at sea.

Apart from geology, one of the guests Eliana Loveluck who is a survivor of the 1960 Chilean earthquake offers this explanation:

Neil Conan: But Eliana Loveluck is still with us here in the studio. I wanted to ask you a question about these building codes. Is this a part of Chilean culture?

Ms. Loveluck: It is. In Chile, we grow up knowing about earthquakes, being told what to do in different situations. I always grew up knowing that if I was at the beach, and I saw water receding, I needed to run the other way because the water was coming back.

But I think what is very important to acknowledge is that Chile has always had a very strong infrastructure, and it has a very well-functioning government, and that infrastructure is prepared and constantly being reassessed in terms of preparedness for dealing with earthquakes.

The other thing that I think is very important to also acknowledge is that Chile is a country with very little corruption. It actually scores very close to the United States, and so it is not a country where you can go and bribe a builder to overlook the codes or anything like that....

Recent earthquake memories, education, better government institutions and low levels of corruption enabling preparedness plans to be effectively implemented.

Haiti suffered from both a geological misfortune of having the epicenter too close to population centers, but also from a total lack of preparedness, a virtual lack of institutional support and extreme poverty leading to poor quality constructions.

India falls somewhere in between Chile and Haiti. It has good institutions and a strong science and engineering backbone. The National Bureau of Standards have long ago formulated earthquake resistance building codes which have undergone periodic revisions. The National Information Center Of Earthquake Engineering at IIT Kanpur has a list of all the earthquake building codes.

So there is no lack of safety codes and regulations. Its the last point Ms. Loveluck points to that India fails miserably namely ....government apathy and corruption. Enforcement of rules is very poor. Its easy to bribe officials into overlooking construction plans that don't follow stringent earthquake safety codes. That and a lack of expertise at the municipality level,  where building plans get clearance, in assessing what exactly an earthquake safe building should be given local conditions.

I found a couple of links which point to these problems. This article explores how post-Bhuj earthquake, plans to revise and implement earthquake safety codes stalled as a result of bureaucratic red tape and political manipulations of development rules.

And this article describes the situation in Delhi which launched an ambitious seismic vulnerability micro-zonation mapping plan in 2001. It has still not been completed and revision of building safety regulations supposed to be based on that plan remain in limbo.

Meanwhile tens of thousands of new buildings have come up in an area classified as a seismically active zone, just 150 km from some major Himalayan faults. One can only guess at the safety standards being adhered to and the potentially catastrophic cost of this inaction.

Genetic History Of Indian Populations

Partha P. Majumder summarizes population level genetic data from south Asian populations in a special issue of Current Biology on Archaeogenetics, the attempted synthesis of archaeology and genetics. The paper is open access.

South Asia — comprising India, Pakistan, countries in the sub-Himalayan region and Myanmar — was one of the first geographical regions to have been peopled by modern humans. This region has served as a major route of dispersal to other geographical regions, including southeast Asia. The Indian society comprises tribal, ranked caste, and other populations that are largely endogamous. As a result of evolutionary antiquity and endogamy, populations of India show high genetic differentiation and extensive structuring. Linguistic differences of populations provide the best explanation of genetic differences observed in this region of the world. Within India, consistent with social history, extant populations inhabiting northern regions show closer affinities with Indo-European speaking populations of central Asia that those inhabiting southern regions. Extant southern Indian populations may have been derived from early colonizers arriving from Africa along the southern exit route. The higher-ranked caste populations, who were the torch-bearers of Hindu rituals, show closer affinities with central Asian, Indo-European speaking, populations.

Nothing radically new, but its good to have a review article that compiles genetic studies done on extant Indian populations along with references to primary literature.

Missing though from this emerging data bank is ancient - but within a historical time frame- skeletal material and DNA from the subcontinent for comparison, which could potentially answer many vexing and controversial questions about historical migrations into India.

In this regard the recent find of Harappan age skeletons along with pottery and artifacts from Farmana, Haryana about 60 km from Delhi gains significance as recovered DNA from these skeletons could give data about the relatedness of these ancient northwestern Indian populations with Eurasians and central Asians and clarifying to some extent when admixtures of central Asian and Eurasian genes with Indian populations occurred.

There are other excellent articles in this issue. Particularly the one by Pritchard et.al. on The Genetics of Human Adaptation: Hard Sweeps, Soft Sweeps, and Polygenic Adaptation.

Maps Of The Chilean Earthquake

Some maps of the Chilean earthquake:

1)  Henry Fountain of the NY Times writes about the geologic setting of the earthquake accompanied by tectonic and fault maps of the region.

2) The United States Geological Survey has a collection of maps and reports on their earthquake site.

3)  GeoCommons, which is a public mapping site run by FortiusOne, a data visualization company, has a series of interactive GIS layers on Chile. In case you haven't come across GeoCommons, I highly recommend their data Finder and map Maker applications.

February Science Talks Round Up

Some listenable science talks I came across this past month:

1) Steven Strogatz Talks Math - What is the difference between an extroverted mathematician and an introverted mathematician?....the extroverted mathematician stares across at your shoes when talking!  Steven Strogatz who writes on the NY Times Opinionator blog talks engagingly about math, road blocks to understanding it and how it connects seemingly disparate things in life.

2) Darwin and "Creation" - Darwin's great great grandson Randal Keynes and movie director Jon Amiel discuss a movie on Darwin's family life and his work before he wrote up the Origin of Species and became famous. 

3) The Immortal Life Of Henrietta Lacks- In the 1950's researchers took a tissue sample of cervical cancer cells from Henrietta Lacks without her permission and have been using them for research. That was common practice then. But issues of patient consent, privacy, patents and medical ethics intrude on our lives more and more. Science writer Rebecca Skloot talks about them.

4) Communicating Science - With more people turning to the web and blogs for news...can locking yourself in an echo chamber be prevented? Would you end up reading only news and opinions you already agree with..? Will readership be fragmented on ideological lines to the point of no return?...the recipe I follow..Educate yourself...listen and read from multiple sources...take the time to read views contrary to your personal biases and pet theories...keep an open and skeptical mind.

I use these guiding points no matter what I am reading..."reputable" mainstream media articles or blogs or twitter feeds.