Palaeoclimate: The rhythm of the rains

The Asian monsoon influences a vast area. Understanding how it has changed in the past explains a great deal about climate change, the landscape of the Asian continent, and also cultural adaptation to these environments...

Deposits in a Chinese cave tell the story of the region's climate stretching back more than 200,000 years, well past the last interglacial warm period — an invaluable resource for understanding the Asian monsoon.

In the quest to understand past climate change, and thus to anticipate future trends, records from cave deposits — speleothems — are increasingly taking centre stage. Wang et al.¹ present a virtuoso study: a 224,000-year chronicle of the past variability of the East Asian monsoon, recorded in the oxygen isotope ratios of stalagmites built up from the floor of the Sanbao Cave in eastern central China. This is the latest in a series of records^{2, 3, 4, 5, 6, 7} from Chinese caves that has illuminated the workings of the East Asian monsoon, over timescales ranging from thousands of years to tens of millennia. Much remains to be understood, but the significance of this work extends well beyond the caves and the monsoon that feeds them. It provides yet more backing for a once-daring hypothesis: that wobbles in Earth's passage around the Sun are a prime mover of long-term monsoon variation.

As Earth moves around the Sun, its orbital eccentricity (the deviation of its path from a perfect circle) and its obliquity (the tilt of its rotational axis) vary slowly over time. The axis of its rotation also wobbles like that of a spinning-top, a phenomenon known as precession. These effects combine to induce a 23,000-year quasi-periodicity in the distribution of incoming solar radiation (insolation). At different stages of this slow precessional cycle, insolation at a particular place on Earth's surface may be strongest during winter, summer, or somewhere in between.

In 1981, John Kutzbach recognized⁸ that the changing seasonal contrast in insolation might have a significant effect on the Asian monsoon, which is driven by different rates of seasonal heating over the continents and the oceans. By taking the values for the amount of radiation hitting Earth 9,000 years ago — when the Northern Hemisphere was closer to the Sun in summer than it is today, and the influence of glacial ice from the preceding ice age had all but disappeared — and plugging them into a climate model, he calculated that the Asian monsoon circulation must have been more intense at that time than it is today. That result matched observations that rainfall was greater in many areas of the tropics between 10,000 and 5,000 years ago. Various data sets have since been used to establish the details of this relationship over many precessional cycles.

Compared with other stalwart proxies of palaeoclimatology — records from tree-rings, sediments, ice cores, corals and the like — speleothems are relative newcomers. Like many proxies, they record the ratios of different oxygen isotopes in material laid down over time. These ratios are sensitively linked to the composition of precipitation, and thus to the prevailing climate. There are valuable examples of speleothem records from most continents, from mid-latitudes into the tropics, but few regions have proved to be as fertile as eastern China. Among the exciting records stored here are several from the Dongge Cave that span the Holocene, the interglacial period from 11,550 years ago to the present^{3, 6}. These complementary records elegantly confirm the orbital theory of monsoon variability, but also reveal decade- to century-scale variability that differs between geological formations (Fig. 1).

A comparison of oxygen isotope ratios (expressed as ¹⁸O) from Sanbao¹ (two records) and Dongge^{3, 6} caves in eastern China over the Holocene period yields clear trends in agreement with millennial-scale decline in insolation¹⁶ (in July at 30° N; pink line), caused by variations in Earth's orbit. The mean values are offset between the two caves owing to differences in elevation and temperature¹. Century-scale variance is not always consistent among the records, highlighting the need for replication to isolate climate signals that are uniform over whole regions.High resolution image and legend (47K)

Speleothems work best when there are consistent conduits for moisture to work its way through soil and rock into a relatively closed cave where, drip by drip, it contributes to the build-up of stalagmites. As carbon dioxide is lost from this dripwater, calcium carbonate (CaCO₃) precipitates. Many factors, including evaporation in soil and the nature of the cave environment, can change the oxygen isotope composition of the water after it leaves the atmosphere^{9, 10}, interfering with the primary climatic signal. The robustness of a speleothem as a climate record thus depends on a large signal-to-noise ratio and on replication and/or calibration to identify clear climate signals.

Wang and colleagues' Sanbao Cave record¹ shows that essential aspects of past monsoon variability can be replicated not just within a single cave, but also between widely spaced caves in the same region: the monsoon signal swamps non-climatic and local noise over the long timescales of orbital change. What emerges is a record of monsoon variation unprecedented in its detail and chronology stretching back 224,000 years. The primacy of orbital precession in driving the monsoon with a quasi-periodic beat of approximately 23,000 years is nicely revealed, as are details of millennial monsoon variability that show the influence of changed ocean circulation in the North Atlantic during glacial periods.

These results bring into sharp relief the true power of speleothems: the ability to date their records precisely. This is made possible by measuring the growth of the isotope thorium-230 from the slow radioactive decay of uranium, which is incorporated in trace amounts in the speleothem deposits. This method works for samples hundreds of thousands of years old, far beyond the limit of about 50,000 years that radiocarbon dating allows. Until now, the best well-dated, high-resolution records of climate variability from the Northern Hemisphere have been those from the long cores extracted from the remote Greenland ice cap. These justly famous records extend back only into the last interglacial period, less than 125,000 years ago, and uncertainties in the models used to date the cores remain above the precision possible with uranium–thorium dating¹¹.

The Sanbao Cave record reveals that there is more to monsoon variability than a simple linear response to precessional climate effects. Precession unsurprisingly controls the largest changes in amplitude in the Asian monsoon, by altering the supply of latent heat from the Southern Hemisphere or the amount of heating over the adjacent, 5,000-metre-high Tibetan Plateau, or possibly both^{8, 12, 13}. But the maximum-insolation peak during the last interglacial seems to have produced a weaker monsoon than smaller insolation maxima during the glacial period that preceded it. The monsoon response is also far less uniformly sinusoidal than the precession-induced variation in insolation, making it hard to judge the true nature of the phasing between the two effects. Work to unravel these mysteries will have to tap a variety of proxy sources and elaborate on the mechanisms linking monsoon variability to broader climate variability^{14, 15}.

The smaller-amplitude, higher-frequency variations of the monsoon that occurred during both glacial and interglacial periods are even more of a challenge: here, the discrepancies between individual Sanbao records, just as with the Dongge data, indicate that details may be clouded by the smaller apparent signal-to-noise ratio (Fig. 1). Is the problem related to noise associated with cave processes? Or is it simply that smaller changes in climate forcing yield a monsoon response that varies more from place to place than is supposed? The answer will come from continuing to build up a network of data from different proxy sources, such as speleothems and lake and marine sediments, that covers the most recent glacial cycle, and especially the past 10,000 years.

The foremost goal is, of course, to anticipate how the Asian monsoon might change in the future. One thing seems certain: the monsoon is sensitive to climate changes, and if the future brings a sufficiently large net increase in summer heating of the Tibetan Plateau, its response could be large and relatively homogeneous. That could be good for those living in the shadow of the monsoon who need more rainfall. But a stronger monsoon would be hard on those in parts of south and east Asia already plagued by summer flooding. As sea levels rise along with monsoon floodwaters, the low-lying areas draining monsoon Asia could be especially at risk.

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The aftermath of independence

Not everyone is happy with Kosovo's independence...

The formerly Serbian province of Kosovo unilaterally declared its independence on 17 February. Some 10,000 Serbian students and academics live in enclaves in the ethnically divided city of Kosovska Mitrovica in the north of the new country dominated by Kosovar Albanians. Endocrinologist Aleksandar Jovanovic, vice-rector for science and international relations at the University of Mitrovica, discusses recent events.

What is the University of Mitrovica's set-up?

We were the University of Priština, but during the war in 1999 the university was split, and the main Serbian part was re-established in Mitrovica in 2001 [where it goes by the protracted name of the University of Priština in Kosovska Mitrovica]. The university is licensed by the United Nations Mission in Kosovo and funded by the Serbian government, at a cost of around €10 million (US$14.8 million) per year, which is spent mostly on salaries. We have around 10,000 students and 700–800 professors, who are paid a 100% 'Kosovo bonus' to work and teach here. The university has ten departments including faculties for science, medicine, engineering, economics and agriculture.

How did you react to the declaration of independence?

It is our clear wish to stay with Serbia. There is no way that professors or students here would teach, or get taught, in a Kosovar-Albanian-led educational system. It just wouldn't work. We have very different traditions, and we haven't had any contact with the Kosovar Albanian academic community for years. Unfortunately, there are broader political interests that are currently a higher priority than university affairs.

What are your main concerns?

In an independent Kosovo we're expecting all kinds of difficulties. Luckily, Serbia says it will continue to support our work. We need to remain a Serbian institution, otherwise this university will just cease to exist. We cannot survive without Serbian support. At the moment our main concern is security. There haven't been major clashes since March 2004, when there were attacks on the Serbian communities in Kosovo. The unilateral declaration of Kosovo's independence means that there is potential for violent conflict once more. Political rhetoric is up, anything can happen.

Students are leading the protests in Mitrovica against Kosovar independence. Is the university term being interrupted?

We're midway through the spring term and we're doing our best to carry on teaching. Student protests began on 18 February, the day after the declaration of independence, and have been going on every day since. But lectures are taking place as usual. There are courses until noon, then the students — between 3,000 and 5,000 each day — take to the streets until 3 p.m., and then everybody comes back for the afternoon classes. We must keep up the work, or we will pay the price later. When we allowed protesting students to proceed to the next term without any exams in 1996, it took several years to return to academic order.

Has there been violence?

The student protests have mostly been peaceful. There was one incident on Saturday [23 February] when some radicals tried to provoke police, throwing bottles and fake bombs. We don't know whether there were any students involved, though.

Why is the university so important for the Serbs in Kosovo?

It is vital for the Serbian enclaves in northern Kosovo. It is the only strong economic factor in a region where just 8% of the economy is private sector. Without the university, the 100,000-strong Serbian minority would further evaporate. We need the students, and we hope that many will stay here after graduation and help keep the economy alive.

Is any scientific research now going on at the university?

We're mostly just teaching. There are 46 small scientific projects, many of which were started before we moved from Priština in 1999. We have a collaboration in material sciences with Queen's University in Ontario, Canada, and we have partnerships with universities in Serbia, Macedonia, Greece and Bosnia. We're also hoping to launch a collaboration with the University of Grenoble in France. Health and environmental issues related to the mining activities in the region could be a priority for future research activities.

What difficulties do you face?

We're working under chaotic conditions. The biggest problem is that our infrastructure is devastated and that our labs are very poorly equipped. There is a lack of everything, from lighting, to computers, to chemicals. Part of our equipment, such as computers and lab tools, are locked in Priština. We have been trying to get it back or be reimbursed, but so far without success.

Is there any contact between Serbian and ethnic Albanian scientists in Kosovo?

There hasn't been any cooperation between the universities of Priština and Mitrovica since the Serbian community had to leave Priština in 1999. I hope that in the future we will collaborate with Albanian-language scientists and academics again.

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Killer instincts

How violent are we? Are we less violent than we used to be? Where does genetics fit into this equation?

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Close to Armageddon?

Asteroid zooms past Earth

Yes folks, it came within half a million km of us! Did you feel the wind in your hair???

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Like sand through the hourglass

Fractals in the sand

Gas fingers in glass beads confirm fluid-theory prediction.

Researchers have confirmed a previously unobserved property of fluids by watching the fractal expansion of a pocket of gas into a thin layer of glass beads.

The experiment adds detail to the understanding of a phenomenon called ‘viscous fingering’, which has been studied for more than 50 years. When two fluids with different viscosities are mixed together, the more freely flowing fluid expands in finger-shaped intrusions into the other fluid. This has been observed in many different systems, including between fine grains such as sand.

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Exercise is good for you

You don't say... but hey, now there's genetic evidence too!

Live slow die young

Sedentary lifestyles could make you old before your time.

Active people could be up to 10 years 'younger' than couch potatoes, at least according to one measure of biological age.

Tim Spector, director of the Twin Research Unit at St Thomas’ Hospital in London, looked at the levels of physical activity of 2,401 twins and assessed the length of their telomeres - the 'caps' on the ends of their chromosomes that help to protect the DNA from wearing down during the replication process that replenishes cells. Telomeres shorten over an individual’s lifetime and are thought to function as a marker for ageing. Smokers and obese people were already known to have shorter telomeres than their healthier counterparts.

The team found that, on average, telomeres in the most active group (who took more than 3 hours 20 minutes of exercise a week) were 200 nucleotides longer than that of the least active group (who took less than 16 minutes exercise a week).

This difference suggests that inactive subjects may be biologically older by 10 years compared with more active subjects.

Exercise is good for you

The researchers also looked at matched pairs of twins and found an average difference of 88 nucleotides between the more and less active siblings.

The group cannot be certain from this that activity levels are having a direct impact on telomere length. “We can’t prove that," admits Spector. But they think it is the most likely explanation; the researchers corrected their statistics for the impact of smoking, obesity, social status and a whole host of other possible confounding factors. "It’s very hard to think of anything else that would be a confounder that we haven’t measured,” he says.

If inactivity is to blame, Spector can think of a couple of ways in which it might work. It is known that the faster cells are replenished, the faster telomeres shrink, and it's possible that physically inactive people are for some reason experiencing a high cell turnover. Another possible explanation lies in oxidative stress — in which more reactive oxygen atoms or oxygen molecules are created and stress the cells. “It’s possible we need exercise to damp down oxidative stress,” says Spector. Alternatively, it could be that a little bit of oxidative stress is caused by exercise, but that this little bit of harm does some good to our cells.

Invisible factors

In an editorial alongside Spector’s paper, Jack Guralnick, chief of the Epidemiology and Demography Section at the National Institute on Aging in the United States, says more work is needed to pin down whether there is a causal link².

“It’s a provocative finding,” he says. “The statistical association is there; it’s quite clear in the work.” But other diseases that weren’t corrected for could be causing the association, he says. “Proving causality in this kind of study is nearly impossible,” says Guralnick.

Spector admits that his findings will excite debate in researchers who study ageing; the idea that telomere length is directly related to ageing isn't fully accepted. “There’s still controversy,” he says. “When I write that in papers you get one in three reviewers being angry about it.”

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Have humans changed the face of the Earth so dramatically as to justify a new chapter in the history of Earth??

http://www.theaustralian.news.com.au/story/0,25197,23124483-12332,00.html

Scientists argue for redraw of Earth's time line

A HEATED scientific row is brewing as British geoscientists lead a push to establish a new chapter in the history of Earth - one based on human activity.

Led by geologist Jan Zalasiewicz, of the University of Leicester, the rabble-rousers argue that changes wrought since the Industrial Revolution 200 years ago are so profound they are now visible in the physical and living fabric of the planet.

As a result, they have called for the creation of a new Epoch in the official geological time scale, one they have named the Anthropocene.

Along with Eons, Eras, Periods and Ages, Epochs are classifications of Earth history based on characteristic changes in the layers, or strata, of rocks.

Writing in the latest issue of GSA Today, a publication of the Geological Society of America, Dr Zalasiewicz and 20 like-minded experts claim there is "sufficient evidence" of human-induced changes to plants, animals, oceans and lands to warrant recognition of the Anthropocene by the official geological time lords, the International Commission on Stratigraphy. Their proposal came at the same time as the American Geophysical Union at the weekend released its updated position on climate change.

As the AGU represents the largest society of Earth and space scientists, the statement lent weight to the case for the Anthropocene. In its position, posted online, the AGU says: "The Earth's climate is now clearly out of balance and is warming. With climate change ... the human footprint on Earth is apparent."

Detailed scientific arguments for designation of the Anthropocene are expected to be thrashed out in August at the 33rd International Geological Congress meeting in Oslo, Norway.

"I'll be there," said Jim Gehling, a geologist with the South Australian Museum in Adelaide.

And he'll be barracking against the new Epoch.

"This is just the vanity of the human species ... it matters to us but is irrelevant to the planet," Dr Gehling said.

"We don't need a geological Epoch to describe a single historical event, however long- or short-lasting it might be."

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Planetarium closing - noooooo!

As soon as you discover something cool in Canberra, it disappears...

The Canberra Planetarium and Observatory in Downer, beloved for its quaint stargazing documentaries and fantastic suite of telescopes for checking out nebulae, is due to close at the end of this month. The Tradies Club in Dickson, which owns the site, is planning to put something exciting like apartments in.

The Club has very kindly offered to donate the equipment to any organisation in the ACT that has the resources and is prepared to house, maintain and operate this valuable educational and community facility. To facilitate the relocation process, some local astronomers and concerned citizens have formed an association called the Planetarium and Observatory Association of Canberra (POAC). They intend to explore any existing government, educational and community support and to research potential funding sources. POAC membership is open to anybody interested in supporting this cause. It costs $2 to join, more information is available through eye_see_ewe[at]hotmail.com

http://the-riotact.com/?p=6663

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Creationists launch "science" journal

Those tricksy creationists are at it again folks - this time with a peer-reviewed journal which non-scientists won't be able to distinguish from a real science journal...

Answers in Genesis, a Christian ministry run by evangelical Ken Ham, launched Answers Research Journal (ARJ ), a free, online publication devoted to research on “recent Creation and the global Flood within a biblical framework”. Papers will be peer reviewed by those who “support the positions taken by the journal”.

“There have been these kinds of publications in the past,” says Keith Miller, a geologist at Kansas State University in Manhattan, who follows creationism. For the most part, he says, the work is ignored by the scientific community. But those without a science background, including some policy-makers, may not be able to judge the difference in value of a paper in ARJ and a genuine science journal.

Yes folks, this is the bit that concerns me most. Policy which relies on scientific knowledge is guilty enough of watering things down at times - and now there's a new, insidious threat to the contribution genuine science can make.

http://www.nature.com/news/2008/080123/full/451382b.html

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Another sex story for the week?

Syphilis - spoil of the New World?

Genetic study blames Columbus for bringing syphilis to Europe.

For more than 500 years, Christopher Columbus has been alternately blamed and exonerated for bringing syphilis to Europe. Now, a genetic analysis of the disease-causing bacteria shows that today's syphilis is a close cousin to the South American tropical disease yaws, suggesting that the malady has its roots in the Americas.

And what about this one - glaciers in a hothouse world!?

A large ice cap seems to have formed in Antarctica around 91 million years ago, during a period of extreme greenhouse warming. (This might tie in with our dino stories, since they were strolling around at this time).

Then there's...Why do chimps eat dirt?

Apes might eat soil to activate anti-malarial plants.

Chimpanzees in Uganda have been spotted eating dirt along with fistfuls of leaves. This might help to increase the plants' anti-malarial properties.

A friend of mine who worked in Tanzania mentioned the dirt stalls at the markets - I never realised that geophagy might have benefits!

Finally, some Fuzzy Sceptic...

Time is running out for paranormal prize

Challengers for the US$1-million prize offered by the James Randi Educational Foundation for proving paranormal powers have just over two years left to claim the cash. Randi has announced that the paranormal-activity challenge, in which contestants must demonstrate their powers 'under proper observing conditions', will end on 6 March 2010 — exactly 12 years after he first offered up the prize money.

Randi says that the challenge was intended to tempt high-profile paranormal-activity celebrities to come forward. In 2007, Randi changed the rules of the prize so that applicants were only eligible to enter if they had a media profile and some form of academic endorsement. But as the prize remains unclaimed, and the highest-profile celebrities have not entered, Randi would rather the million dollars were freed to be used elsewhere in his foundation, he says.

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Where do the penguins go when there is no ice any more?

Antarctic ice melt accelerating.

A fuzzy community message about climate change...

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Time for revolution in evolution

I've worked out the hyperlink thing, but am not sure if the links will work since I'm going through the ANU Library subscription service for New Scientist. So I've included the text here.

Did life begin on a radioactive beach?

Life's ingredients could have emerged among the radioactive sand grains of a primordial beach laced with heavy metals and pounded by powerful tides...

DID life on Earth begin on a radioactive beach� That's the claim of one astrobiologist, who says that life's ingredients could have emerged from the radioactive sand grains of a primordial beach laced with heavy metals and pounded by powerful tides.

Any origin of life theory needs to explain how the building blocks of cells – such as amino acids and sugars – assembled into complex molecules, and how certain elements came to be incorporated. Though radiation might seem an unlikely source to kick-start such processes because it breaks chemical bonds and shatters large molecules, including DNA, it can provide the chemical energy needed to produce life's building blocks.

Natural “nuclear reactors” were active in the past, such as the uranium ore seam in Oklo, Gabon, which regulated the fission of uranium in a similar way to nuclear-powered submarines (New Scientist, 6 November 2004, p 12). However, conditions at the time life emerged were thought to be unsuitable for concentrating uranium sufficiently to form a reactor that would provide enough energy to create the molecules necessary for life. For instance, a lack of atmospheric oxygen would have prevented uranium becoming water-soluble, so it could not be transported and deposited in rock to form seams like the Oklo reactor.

Now Zachary Adam at the University of Washington in Seattle claims that tidal processes could have concentrated radioactive grains of uranium on a primordial beach, where they may have helped to generate life's building blocks. (Astrobiology, vol 7, p 852). Powerful tides generated by the moon's closer orbit to the Earth compared with today could have sorted the radioactive minerals from other sediments and deposited them along the beach's high-tide mark, he says. According to his computer models, a deposit of radioactive grains could experience the same self-sustaining fission reactions as a seam of uranium.

Adam also designed laboratory experiments with radioactive sand to simulate a beach environment, and found that such a setting would provide the chemical energy to generate some biological molecules in water, such as acetonitrile, which can produce amino acids and sugars when irradiated. Adam says that the radioactive mineral monazite would also release another of life's key ingredients – soluble phosphate – into the regions between the sand grains, making it biologically “accessible” in the water. “Amino acids, sugars and [soluble] phosphate can all be produced simultaneously in a radioactive beach environment,” he says. Furthermore, he says that radioactive actinides such as thorium and uranium could have formed one part of “organometallic complexes” – made up of a metallic ion and an organic molecule. These could have catalysed crucial biological reactions long before the emergence of enzymes.

John Parnell, a geologist at University of Aberdeen in the UK, is intrigued by the theory. “Such a mechanism may provide the crucible for life on any wet rocky planet,” he says, so long as the planet is large enough for the volcanism associated with plate tectonics, which brings radioactive minerals to the surface.

Also in New scientist this week:

FIFTY years ago, evolutionary theory viewed nature through a lens of benevolence: individuals acted for the good of their group, ensuring its survival. This idea, called group selection, did not last out the 1960s. It was swept away by an intellectual revolution which argued that natural selection at the level of genes is what really counts.

This “gene's eye” approach sees attributes that benefit society accruing via bottom-up processes. Altruism, for example, which keeps the wheels of society turning but puts many individuals at a disadvantage, is explained through ideas such as kin selection. This proposes that animals help their relatives in order to pass on shared genes, so what looks like altruism is really the selfish gene in action.

Now, a counter-revolution is being fomented. Late last year, the Harvard biologist Edward O. Wilson co-authored an article in support of group selection (New Scientist, 3 November 2007, p 42). This week, we report that Wilson now thinks kin selection plays an insignificant role in the evolution of colonies formed by social insects (see “Kinship doesn't matter – how insects are altruistic”).

Does this mean evolution itself is in doubt� Certainly not. The debate is akin to physicists questioning the nature of gravitational attraction: nobody disputes that gravity exists, but pinning down its true character should deliver deep new insights.

Wilson has already met serious opposition (see “The evolution of altruism – what matters is gene selection”) and is certain to attract more. Yet such is his standing that we are almost certainly in for a thorough re-examination of group and kin selection. If this elucidates evolutionary processes and gives us that extra insight, it can only be a good thing.

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Did insect bites hasten demise of dinosaurs?

Did insect bites hasten demise of dinosaurs?
James Randerson, London
January 8, 2008

THEY were the most imposing and terrifying creatures to walk the earth, but according to a new theory the dinosaurs might have been pushed towards extinction 65 million years ago by insects.

During the later part of the dinosaurs' dominion over the land, insects underwent an explosion in diversity, dealing a double whammy to the lumbering giants — they spread disease and contributed to a change of vegetation to which the plant-eating reptiles failed to adapt.

The hypothesis is made in a new book by entomologists George and Roberta Poinar. The former is a professor of zoology at Oregon State University.

"We can't say for certain that insects are the smoking gun, but we believe they were an extremely significant force in the dinosaurs' decline," Ms Poinar says. "Our research with amber shows that there were evolving, disease-carrying vectors in the cretaceous (period) and that at least some of the pathogens they carried infected reptiles. This clearly fills in some gaps regarding dinosaur extinctions."

In the gut of one biting insect preserved in amber — fossilised tree sap — from that era, the team has found the pathogen that causes the parasitic disease leishmaniasis and in another a type of malaria parasite that infects birds and lizards. By inspecting fossilised dinosaur faeces, the team also found parasitic microbes carried by insects.

Apart from spreading disease, the insects were busy pollinating flowering plants. These gradually supplanted seed ferns, cycads and gingkoes. If herbivorous dinosaurs could not adapt to this new diet they would have starved.

Ms Poinar believes the most popular theory for the dinosaurs' demise — that a meteorite impact changed the global climate — falls short because the extinction took too long.

"Other geologic and catastrophic events certainly played a role. But, by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years. Insects and diseases do provide that explanation."

This could be a fun story to discuss. I'm just wondering though:

1. "at least some of the pathogens affected reptiles" - yep, and maybe others affected the proto-mammals, who survived. As did smaller reptiles (yet the tiny dinosauria didn't?) and birds. I'm no extinction expert, but this seems a bit simplistic. Mind you, the insects changing the environment bit makes some more sense - might have been a bit too much for the bigger guys to bear (shades of megafaunal extinction in Australia? There's an argument in Quaternary circles suggesting that the big mammals which became extinct around the same time as humans first arriving on the continent might have been "encouraged" towards extinction by alteration of habitat through human use of fire - among other things such as hunting and climatic change...).

2. "Other geologic and catastrophic events certainly played a role. But, by themselves, such events do not explain a process that in reality took a very, very long time, perhaps millions of years..." - um, as far as I know (and I'm speaking as a geochronologist here - this is my job!), we don't have the chronological resolution to know whether the extinction took millions or thousands of years, or even days - we're talking about something that happened 65 MILLION years ago and the best we can do is date that to plus or minus 10%. So we can't pin it down. Palaeontologists may have more to say about dinosaur diversity towards the end of the Cretaceous - perhaps we should check up to see whether it was in decline, but that's not something I recall from my first year geology. I still reckon a monstrous meteorite wholloping the Earth is going to cause some severe climate and habitat change, regardless of what the bugs had been doing for tens of millions of years prior to that.

Happy presenting!
Kat F

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