PALAEOBLOG

Today In History: Darwin Starts "The Origin of The Species"

2008-05-14T08:25:00.000-04:00

Today In Science History tells us that in 1856, Charles Darwin began writing his book, The Origin of Species, sitting in the study of his country home in Down, England.

So all you graduate students surfing the web -- back to work!

Preservation of Ancient Biomolecules

2008-05-13T19:50:00.004-04:00

Paleo © Jim Lawson

The latest issue of Comptes Rendus Palevol has a number of articles on ancient biomolecules and their preservation:

Environment and excavation: Pre-lab impacts on ancient DNA analyses. 2008. Ruth Bollongino et al. Comptes Rendus Palevol

Abstract: Ancient DNA (aDNA) analyses enjoy an increasing role in palaeontological, archaeological and archaeozoological research. The limiting factor for aDNA studies is the degree of DNA preservation. Our study on 291 prehistoric cattle remains from Europe, the Near East and North Africa revealed that DNA preservation is mainly influenced by geographic and climatic conditions. Especially in hot climates, the preservation of sample material is generally low. We observed that these specimens are prone to further degradation and contamination during and after excavation. We give a description of the main caveats and a short guideline for adequate sample handling in order to facilitate the cooperation between archaeologists and geneticists and to improve the outcome of future research.

Comparing rates of recrystallisation and the potential for preservation of biomolecules from the distribution of trace elements in fossil bones. 2008. Clive N. Trueman, et al. Comptes Rendus Palevol

Abstract: Preservation of intact macromolecules and geochemical signals in fossil bones is mainly controlled by the extent of post-mortem interaction between bones and sediment pore waters. Trace elements such as lanthanum are added to bone post-mortem from pore waters, and where uptake occurs via a simple process of diffusion and adsorption, the elemental distribution can be used to assess the relative extent of bone-pore water interaction and rate of recrystallisation. Distribution profiles can be parameterised effectively using simple exponential equations, and the extent of bone–water interaction compared within and between sites. In this study, the distribution of lanthanum within bone was determined by laser ablation ICP–MS in 60 archaeological and fossil bones from Pleistocene and Cretaceous sites. The rates of recrystallisation and potential for preservation of intact biogeochemical signals vary significantly within and between sites. Elemental profiles within fossil bones hold promise as a screening technique to prospect for intact biomolecules and as a taphonomic tool.

Microscopic, chemical and molecular methods for examining fossil preservation. 2008. Mary Higby Schweitzer et al. Comptes Rendus Palevol

Abstract: Advances in technology over the past two decades have resulted in unprecedented access to data from biological specimens. These data have expanded our understanding of physical characteristics, physiological, cellular and subcellular processes, and evolutionary relationships at the molecular level and beyond. Paleontological and archaeological sciences have recently begun to apply these technologies to fossil and subfossil representatives of extinct organisms. Data derived from multidisciplinary, non-traditional techniques can be difficult to decipher, and without a basic understanding of the type of information provided by these methods, their usefulness for fossil studies may be overlooked. This review describes some of these powerful new analytical tools, the data that may be accessible through their use, advantages and limitations, and how they can be applied to fossil material to elucidate characteristics of extinct organisms and their paleoecological environments.

Big Mammals Evolve & Die Out Faster

2008-05-11T10:29:00.002-04:00

Higher origination and extinction rates in larger mammals. 2008. L.H. Liow et al. PNAS 105: 6097-6102.

Jimmy Olsen © DC Comics

Abstract: Do large mammals evolve faster than small mammals or vice versa?

Because the answer to this question contributes to our understanding of how life-history affects long-term and large-scale evolutionary patterns, and how microevolutionary rates scale-up to macroevolutionary rates, it has received much attention. A satisfactory or consistent answer to this question is lacking, however.

Here, we take a fresh look at this problem using a large fossil dataset of mammals from the Neogene of the Old World (NOW). Controlling for sampling biases, calculating per capita origination and extinction rates of boundary-crossers and estimating survival probabilities using capture-mark-recapture (CMR) methods, we found the recurring pattern that large mammal genera and species have higher origination and extinction rates, and therefore shorter durations.

This pattern is surprising in the light of molecular studies, which show that smaller animals, with their shorter generation times and higher metabolic rates, have greater absolute rates of evolution.

However, higher molecular rates do not necessarily translate to higher taxon rates because both the biotic and physical environments interact with phenotypic variation, in part fueled by mutations, to affect origination and extinction rates.

To explain the observed pattern, we propose that the ability to evolve and maintain behavior such as hibernation, torpor and burrowing, collectively termed "sleep-or-hide" (SLOH) behavior, serves as a means of environmental buffering during expected and unexpected environmental change. SLOH behavior is more common in some small mammals, and, as a result, SLOH small mammals contribute to higher average survivorship and lower origination probabilities among small mammals.

The Last Dino Manga

2008-05-10T20:15:00.003-04:00

At least for a while. I confess that I'm not much of a manga fan, but I appreciate the author's love of dinos. And how often do you see a champsosaur in any book?

I'm out of town for a while and will post when I can.

Andy Farke, Ph.D.

2008-05-09T17:07:00.002-04:00

A round of applause for Andy Farke who jumped through the final hoop and successfully defended his Ph.D. yesterday at SUNY. Was there ever any doubt?

Andy will soon be off to his new job at the Raymond M. Alf Museum in California.

Behold! Coprolite 1374-5/5D-31-2!

2008-05-09T08:00:00.002-04:00

DNA from Pre-Clovis Human Coprolites in Oregon, North America. 2008. M. Gilbert et al. Science 320: 786-789.

Coprolite 1374-5/5D-31-2

Abstract: The timing of the first human migration into the Americas and its relation to the appearance of the Clovis technological complex in North America at about 11,000 to 10,800 radiocarbon years before the present (¹⁴C years B.P.) remains contentious.

We establish that humans were present at Paisley 5 Mile Point Caves, in south-central Oregon, by 12,300 ¹⁴C years B.P., through the recovery of human mitochondrial DNA (mtDNA) from coprolites, directly dated by accelerator mass spectrometry.

The mtDNA corresponds to Native American founding haplogroups A2 and B2. The dates of the coprolites are >1000 ¹⁴C years earlier than currently accepted dates for the Clovis complex.

Atomic Surgery had more interesting coverage of this last month.

Piltdown Comic

2008-05-09T00:25:00.000-04:00

Thanks to The Comics Reporter I found out about “Piltdown”, a free comic book anthology of "prehistoric times", as the publisher, Wide Awake Press describes.

“Megatherium, Terror of the Ice Age” by Ben Towle is hilarious! Download the book to read the entire strip.

You can read or download the book HERE

Platypus Genome Unravels Mysteries of Mammalian Evolution

2008-05-08T09:41:00.004-04:00

Genome analysis of the platypus reveals unique signatures of evolution. 2008. Everyone and their dog. Nature 453: 175-183.

Zina Deretsky, National Science Foundation

Platypus DNA reveals its shared history with bird, reptilian and mammalian lineages.

From the press release:

The first genome sequencing project of a mammal that lays eggs, confirms that platypus DNA looks like something of a patchwork.

"Their genomic organization was strange and a little unexpected," says Batzer. "It appeared much more bird- and reptile-like than mammalian, even though it is indeed classified as a mammal."

The platypus occupies the first branch of the mammalian tree of life after the split from "sauropsids" about 315 million years ago. It maintains some long dated features and, as a result, should provide information on how mammals evolved.

One interesting finding for the researchers is that several of the populations seem to have been geographically separated for a long time. Based on an analysis using mobile elements, the population on the island of Tasmania seemed genetically far-distanced compared to other platypus populations from the mainland of Australia.

Platypuses are extremely shy by nature and only a few places like Healesville Sanctuary in Victoria, Australia, have had success breeding them in captivity.

Researchers hope that some of the clues unearthed in the platypus genome might lead to a better understanding of the history of the species and new conservation efforts.

Credit: Healesville Sanctuary, Victoria, Australia

Genome Research is also publishing several related articles including:

Bird-like sex chromosomes of platypus imply recent origin of mammal sex chromosomes. 2008. F. Veyrunes et al. Genome Research.

Therian mammals possess an XY sex-determination system, where females have a pair of X chromosomes, and males harbor one X and one Y chromosome. However, the sex-determination system of platypus stands in stark contrast: the female has five different pairs of X chromosomes, while males have five X chromosomes and five Y chromosomes. This study found that the platypus sex chromosomes are unrelated to the X or Y chromosomes of other mammals, and lack the mammalian sex determining gene SRY and the gene from which it evolved. Instead, their sex chromosomes share extensive homology to those of birds suggesting that our ancient mammal-like reptile ancestor may have had bird-like sex chromosomes and sex determination system.

Conservation of small RNA pathways in platypus. 2008. E.P. Murchinson et al. Genome Research

This paper found that the platypus shares microRNA families uniquely with other mammals, but also uniquely with a representative of birds and reptiles,” explains Hannon. “Thus, the unusual morphology of these animals is also reflected at the genomic level and at the level of its small RNAs.”

See also:

Retroposed SNOfall – A mammalian-wide comparison of platypus snoRNAs. 2008. J. Schmitz et al. Genome Research

Origin of INSL3-mediated testicular descent in therian mammals. 2008. J. Park et al. Genome Research.

Defensins and the convergent evolution of platypus and reptile venom genes

A nice summary from Nature

Bug Bites On Dino Bones

2008-05-07T09:12:00.002-04:00

A Suite of Dermestid Beetle Traces on Dinosaur Bone from the Upper Jurassic Morrison Formation, Wyoming, USA. 2008. B. Britt et al. Ichnos 15: 59–71.

My old friend and fellow former Drumhellerite, Brooks Britt (above), makes the news again

From the press release:

BYU professor Brooks Britt and student Anne Dangerfield have investigated insect traces on the 148-million-year-old remains of a Camptosaurus, a plant-eating specimen discovered in Medicine Bow, Wyo., in 1995.

Their analysis revealed that beetles, from the family entomologists call Dermestidae, left the markings on the Camptosaurus. Dermestid beetles still exist today and are typically brown or black, oval-shaped and feed on flesh, hair, skin or horns of carcasses.

Information about the beetle’s typical habitat reveals the climate at the time of the Camptosaurus’ death probably had 60-80 percent relative humidity and a temperature of 77-86 F. By comparison, the average yearly temperature in Medicine Bow is now 43.5 F.

When the dinosaur died near what is now Medicine Bow, the carcass was consumed by other insects. The beetles then infested the Camptosaurus within months of its death.

In addition to shedding light on Wyoming’s ancient climate, Dangerfield and Britt’s work shows dermestid beetles existed much earlier than previously thought. The traces on this Camptosaurus predate the oldest body fossils for dermestid beetles by 48 million years.

Britt and Dangerfield continued their research by looking at more than 7,000 bones from various quarries and found that insect traces on dinosaur bones are quite common, but dermestid beetle traces were found only on the Camptosaurus skeleton from Medicine Bow.

Manga Albertaceratops

2008-05-06T13:39:00.003-04:00

Random pages from volume 4 of Yuta of the Land of Dragons with fun facts about real dinosaurs.

T. rex Discovery Center

2008-05-06T13:27:00.003-04:00

Every time I try to get hold of a colleague in Alberta, they’re always out of town at the The T.rex Discovery Centre in Eastend, Saskatchewan. Why? Well, aside from being a great interpretive centre in a great place, they have “Scotty”, the T. rex.

image

If you're driving across Canada this summer plan to stop in. The T.rex Discovery Centre in Eastend, Saskatchewan has partnered with the Royal Saskatchewan Museum and its Fossil Research Station to create a display highlighting six celebrated scientists who have, over the past 125 years, uncovered Saskatchewan's ancient past. The T.rex Discovery Centre will unveil this wall exhibit May 3, 2008.

"The exhibit will be unveiled Saturday, May 3 and may be viewed during regular Discovery Centre hours from 9 a.m. to 5 p.m.," T.rex Discovery Centre manager Heather Gibson said. "And at 7:30 p.m. we are pleased to present Tim Tokaryk, Palaeontologist with the Royal Saskatchewan Museum who will speak to us on ‘A Passion For Palaeo; 125 years searching for Saskatchewan's past'. This will follow the Annual General Meeting of the T.rex Discovery Centre at 6:30 p.m."

Contact the T.rex Discovery Centre at 306-295-4009. If you see Tim say 'hi' for me.

Schultz's "War That Time Forgot"

2008-05-05T16:57:00.003-04:00

Art © Mark Schultz

Mark Schultz sent along this cover he did for an upcoming issue of "The War That Time Forgot" from DC Comics.

Man vs. mutated pterosaurs - if only the world were this simple again!

Born This Day: Elkanah Billings

2008-05-05T15:53:00.002-04:00

May 5, 1820 - June 14, 1896

From Today In Science History:

Billings was a Canadian geologist and paleontologist, who was the first Canadian paleontologist.He published his first scientific paper on Trenton fossils in 1854. He launched a new monthly periodical, The Canadian Naturalist and Geologist in 1856, which he also edited and was the major contributor.

In Aug 1856 he was appointed staff paleontologist with the Canadian Geological Survey by William Edmond Logan, the founder of the Survey. Billings immediately began the task of identifying a 20-year backlog of fossils collected by the Survey. By 1863 he had published descriptions of no fewer than 526 new species of fossils.

The Billings medal, named in his honour, is awarded annually by the Paleontology Division of the Geological Association of Canada as a means of recognizing the most outstanding of its paleontologists.

On April 27, 1869, the Director of the GSC, Sir William Logan wrote this curt note to the paleontologist Elkanah Billings: "Your constant absence from the office is a worrying annoyance, particularly as I have reason to suspect that it does not arrive from rheumatism".

For more info on Billings click HERE.

Click HERE for more information on the Geological Association of Canada.

Portrait of Elkanah Billings GSC photo 69323 (c)

Born This Day: Thomas Huxley

2008-05-04T13:37:00.001-04:00

May, 4, 1825 -- June 29, 1895.

From the UC Berkeley Page:

Huxley was born in Ealing, near London, the seventh of eight children in a family that was none too affluent. At 21, Huxley signed on as assistant surgeon on the H.M.S. Rattlesnake, a Royal Navy frigate assigned to chart the seas around Australia and New Guinea. Huxley collected and studied marine invertebrates, in particular cnidarians, tunicates, and cephalopod mollusks. After leaving the Navy in 1854, Huxley managed to secure a lectureship at the School of Mines in London.

Huxley was a passionate defender of Darwin's theory -- so passionate that he has been called "Darwin's Bulldog" – and also a great biologist in his own right, who did original research in zoology and paleontology.

He is best known for his famous debate in June 1860, at the British Association meeting at Oxford. His opponent, Archbishop Samuel Wilberforce, was not-so-affectionately known as "Soapy Sam" for his renowned slipperiness in debate. During the debate, Archbishop Wilberforce ridiculed evolution and asked Huxley whether he was descended from an ape on his grandmother's side or his grandfather's. Accounts vary as to exactly what happened next, but according to one telling of the story, Huxley muttered "The Lord hath delivered him into my hands," and then rose to give a brilliant defense of Darwin's theory, concluding with the rejoinder, "I would rather be the offspring of two apes than be a man and afraid to face the truth."

All accounts agree that Huxley trounced Wilberforce in the debate, defending evolution as the best explanation yet advanced for species diversity.

However, Huxley did not blindly follow Darwin's theory, and critiqued it even as he was defending it. In particular, where Darwin had seen evolution and a slow, gradual, continuous process, Huxley thought that an evolving lineage might make rapid jumps, or saltations. As he wrote to Darwin just before publication of the Origin of Species, "You have loaded yourself with an unnecessary difficulty in adopting Natura non facit saltum [Nature does not make leaps] so unreservedly."

Huxley's most famous writing, published in 1863, is Evidence on Man's Place in Nature. This book, published only five years after Darwin's Origin of Species, was a comprehensive review of what was known at the time about primate and human paleontology and ethology. More than that, it was the first attempt to apply evolution explicitly to the human race. Huxley explicitly presented evidence for human evolution.

Huxley founded a remarkable dynasty of English scientists and thinkers. His son Leonard was a noted biographer and "man of letters." Leonard's oldest son Julian was one of the authors of the evolutionary synthesis of the early 20th century; Julian's son Francis became a noted anthropologist. Julian's brother Aldous Huxley was a novelist, screenwriter and essayist; his best-known book is the anti-utopia Brave New World.

Born This Day: Joseph Barrell

2008-05-04T13:35:00.000-04:00

Dec. 15, 1869 – May 4, 1919

From Today In Science History:

Barrell was an American geologist who proposed that sedimentary rocks were produced by the action of rivers, winds, and ice, as well as by marine sedimentation. In 1916, he indicated that the coloration of many Devonian rocks was bright red because they had been baked dry, like bricks, in arid conditions. Also, this severe climate was a driving force in the evolution of air-breathing vertebrates, including tetrapods.

In 1917, he used the new results of radioactive dating to reinterpret Earth's age at a few billion years, though many geologists still preferred an age of 100 million years. Barrell emphasized that geological processes vary in intensity in a cyclical rather than a uniform fashion, thus current rates of geological change should not be used as a guide to the past,as in prior estimates.

Yuta of the Land of Dragons

2008-05-03T15:56:00.007-04:00

Tetsuto Miyashita recently gave me more volumes of the manga series “Yuta of the Land of Dragons - Story of Another World of Dinosaurs” by author and artist Juzo Tokoro is set in the Late Cretaceous of western North America.

I have no idea what’s going on here but the last time I posted about it there was a lot of interest. That's a baby Nanotyrannus on the cover.

A note to parents that there is the occasional decapitation and “arrow-through-the-head” motif running through the series, but, apparently, this kind of thing is mild for a mange series like this.

Is that a lesson on nasal turbinates on the last page?

I'll post a few more dino-centric pages over the next week.

Did Dinosaurs Die In A Fiery Holocaust?

2008-05-03T13:32:00.002-04:00

Combustion of fossil organic matter at the Cretaceous-Paleogene (K-P) boundary. 2008. M.C. Harvey et al. Geology 36: 355-358.

Scientists examining sediments from the end of the dinosaur age has discovered microscopic carbon spheres that can be produced only from burning fossil fuels suggesting that the dinosaurs might have been wiped out at least partly by an oil-fueled conflagration.

From Science Now:

The new potential explanation for the demise of the dinosaur derives from a component of the soot in the K-T sediments: distinctive carbon globs known as cenospheres. The microscopic spheres can form only when fossil hydrocarbons such as coal and crude oil burn.

Cenospheres were found at eight of 13 sites it examined around the world, and the objects were present only at the K-T boundary, not above or below it. The researchers suspect the Chicxulub object plowed into a huge oil reservoir in the Gulf of Mexico, like the ones feeding offshore platforms there today.

The impact first vaporized the oil and then ignited it in the atmosphere, causing an enormous, spreading fireball probably hundreds of kilometers wide. Whether the conflagration was enough to do in the dinos--via fire, soot, or global warming--remains unknown, but it would have spared a variety of critters, including the ancestors of today's mammals.

The paper is an "eye opener," says paleobotanist Peter Wilf of Pennsylvania State University in State College. It makes "a strong case for the true source of the mysterious soot" in the K-T layer and casts doubt "on the venerable global wildfire hypothesis," he says.

Eoconfuciusornis, a primitive confuciusornithid bird from China

2008-05-02T14:02:00.002-04:00

A primitive confuciusornithid bird from China and its implications for early avian flight. 2008. Zhang, F., et al. Science in China Series D-Earth Sciences 51: 625-639.

From the press release:

The new bird, Eoconfuciusornis is the oldest known confuciusornithid, a group unique to China. It therefore represents an early stage in bird evolution. Confuciusornithids lived from 120-131 million years ago and include the oldest birds with horny beaks.

The fossil deposits of Liaoning, called collectively the Jehol Group, span much of the Early Cretaceous. Eoconfuciusornis falls between Archaeopteryx (150 million years) and the bulk of the Liaoning birds (125 million years), and it shows an intermediate stage in the improvement of bird flying capabilities.

Most bird fossils come from the Jiufotang and Yixian groups, dated about 125-120 million years, but the Dabeigou Formation where Eoconfuciusornis was found is 131 million years, so giving a span of 11 million years of evolution of this particular bird group.

Fetch!

2008-05-02T13:43:00.003-04:00

CLICK TO ENLARGE

Another fun cartoon by Pete Von Sholly

Cyclic Comet Impacts Wiped Out Dinos

2008-05-02T13:38:00.003-04:00

The sun’s movement through the Milky Way regularly sends comets hurtling into the inner solar system – coinciding with mass life extinctions on earth.

image

From the press release:

Scientists built a computer model of our solar system’s movement and found that it “bounces” up and down through the plane of the galaxy. As we pass through the densest part of the plane, gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths. The comets plunge into the solar system, some of them colliding with the earth.

We pass through the galactic plane every 35 to 40 million years, increasing the chances of a comet collision tenfold. Evidence from craters on Earth also suggests we suffer more collisions approximately every 36 million years. Professor William Napier said: “It’s a beautiful match between what we see on the ground and what is expected from the galactic record.”

The periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. Our present position in the galaxy suggests we are now very close to another such period.

While the “bounce” effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.

Although this paper is not yet up at Monthly Notices of the Royal Astronomical Society a bunch of Napier’s earlier articles are:

Evidence for cometary bombardment episodes

A mechanism for interstellar panspermia

Extreme albedo comets and the impact hazard

Born This Day: Sir D'Arcy Thompson

2008-05-02T10:04:00.000-04:00

May 2, 1860 – June 21, 1948

From cscs.umich.edu:

D'Arcy Thompson was a British biologist whose masterwork, On Growth and Form, is a profound consideration of the shapes of living things, starting from the simple premise that "everything is the way it is because it got that way." Hence one must study not only finished forms, but also the forces that moulded them: "the form of an object is a 'diagram of forces', in this sense, at least, that from it we can judge of or deduce the forces that are acting or have acted upon it."

Now by "forces" Thompson meant forces, and one of his great themes is the tremendous light cast on living things by using mathematics to describe their shapes and fairly simple physics and chemistry to explain them. In other words, Thompson wrote a thousand page treatise on self-organization long before the word existed.

From Blackwell Publishing:

D'Arcy Thompson found that related species superficially looking very different could in some cases be represented as simple Cartesian transformations of one another. The most thoroughly worked out modern example of this is Raup's analysis of snail shell shapes with a morphospace.

With some simplification, the axes on the fish grids in here or the snails of the morphospace can be thought of as growth gradients. The evolutionary change between the species would then have been produced by a genetic change in the regulatory mechanisms controlling those gradients.

If we looked at these fish without the grids we might think that an evolutionary change from one into the other would be at least moderately complicated. The interest of D'Arcy Thompson's diagrams is then to show that shape changes could have been produced by heterochrony - a change in the rate or timing of development of some cell lines in the body relative to others.

Figure: a D'Arcy Thompson transformational diagram. The shapes of two species of fish have been plotted on Cartesian grids. Image from HERE.

In the Field, At Last!

2008-05-01T17:28:00.001-04:00

While I spent the day working on grant proposals, my team was out collecting part of a small Dunkleosteous:

Published This Day: Species Plantarum by Linnaeus

2008-05-01T11:54:00.005-04:00

image

In 1753, Carolus Linnaeus published the first edition of his Species Plantarum in which he gave systematic names to plants that are still in use today. He was the first to frame principles for defining genera and species of organisms and to create a uniform system for naming them. He is often called the father of classification, and he extended the familiar scheme of dual Latin names to identify animals in 1758. The Species Plantarum was taken by international consent in 1905 as the starting point for modern botanical nomenclature. From Today In Science History.

The Linnean Society

Died This Day: Joseph Leidy

2008-04-30T08:18:00.000-04:00

Sept. 9, 1823 - April 30, 1891

From The Academy of Natural Sciences:

Leidy is known as the "Father of American Vertebrate Paleontology". He described the first relatively complete dinosaur skeleton, Hadrosaurus, and introduced many American and European scientists to the fossil riches of the American West. Leidy's consummate skill in comparative anatomy would allow him to identify and characterize even the most fragmentary fossil material.

Leidy was also the "Founder of American Parasitology," a Professor of Anatomy at the University of Pennsylvania, a pioneering protozoologists, an influential teacher of Natural History, an accomplished microscopist and scientific illustrator, and an expert on a variety of subjects encompasing the earth and natural sciences. He published scientific papers on more than a thousand extinct and living protozoa, fungi and invertebrates and vertebrates as well as an assortment of publications on human biology and medicine. He was also one of the earliest supporters of Charles Darwin.

New Date For Dino Demise

2008-04-29T15:28:00.004-04:00

Synchronizing Rock Clocks of Earth History. 2008. K. F. Kuiper et al. Science 320: 500-504.

Improvement in argon-argon method pinpoints dinosaur demise with unprecedented precision.

Man-eating ankylosaurs!

From the press release:

The argon-argon dating method has been widely used to determine the age of rocks, whether they're thousands or billions of years old. Nevertheless, the technique had systematic errors that produced dates with uncertainties of about 2.5%.

Scientists have lowered this uncertainty to 0.25 percent and brought it into agreement with other isotopic methods of dating rocks, such as uranium/lead dating. As a result, argon-argon dating today can provide more precise absolute dates for many geologic events, ranging from volcanic eruptions and earthquakes to the extinction of the dinosaurs and many other creatures at the end of the Cretaceous period and the beginning of the Tertiary period. That boundary had previously been dated at 65.5 million years ago, give or take 300,000 years.

The best date for the Cretaceous-Tertiary, or K/T, boundary is now 65.95 million years, give or take 40,000 years.

CLICK TO ENLARGE

Argon-argon dating, developed at UC Berkeley in the 1960s, is based on the fact that the naturally-occurring isotope potassium-40 decays to argon-40 with a 1.25-billion-year half-life. Single-grain rock samples are irradiated with neutrons to convert potassium-40 to argon-39, which is normally not present in nature. The ratio of argon-39 to argon-39 then provides a measurement of the age of the sample.

Some comments from the paper on the age of the Chixculbub impact event: