Base of Quaternary, Pleistocene fixed at 2.6 My

Published online by Nature 3 June 2009 | Nature 459, 624 (2009) | doi:10.1038/459624a

Quaternary geologists win timescale vote

by Amanda Leigh Mascarelli


The International Commission on Stratigraphy (ICS) has elected to formally define the base of the Quaternary at 2.6 million years before present, and also to lower the base of the Pleistocene — an epoch that encompasses the most recent glaciations — from its historical position at 1.8 million years to 2.6 million years ago. The decision, finalized on 21 May, will now be passed to the executive committee of the International Union of Geological Sciences (IUGS) for ratification, which is expected in the next month or two.

The vote shifts an 800,000-year slice, formerly part of the Pliocene epoch, into the Pleistocene. "It's kind of a land grab," says Philip Gibbard, a geologist at the University of Cambridge, UK, who has fought for the redefinition since 2001. "But we see it as just putting straight a mistake that was made 25–30 years ago."

In 1985, the beginning of the Pleistocene was defined at 1.8 million years ago, calibrated to an outcropping of marine strata in southern Italy. But some geologists have long felt that was a localized, arbitrary boundary that did not reflect worldwide changes — and argued instead for the 2.6-million-year mark, when the entire planet cooled.

The term Quaternary was adopted in the early 1800s, when geologists divvied up fossil records of Earth's history into four periods: the Primary, Secondary, Tertiary and Quaternary. The first two terms were discarded long ago, and although Tertiary is still sometimes used, in recent decades some geologists came to consider the Quaternary an outmoded relic. In 2004, a major publication left the Quaternary out of the ICS timescale altogether, making it vulnerable to extinction from scientific nomenclature. In place of the Quaternary, it extended the prior 'Neogene', which began 23 million years ago, up to the present. The Quaternary community went into open revolt.

"The geologic timescale is fundamental for expressing the history of the Earth," says Stan Finney, a geologist at California State University in Long Beach and chair of the ICS. "This is our clock — we need the units of our timescale and their boundaries to be precisely defined."


Finney inherited the debate when he took his post at the ICS in 2008, and he vowed to come up with a democratic process to resolve it. After several months of open discussions and formal proposals from the Quaternary and Neogene communities, two rounds of voting took place, in April and May. The redefinition proposal passed with approval from 16 of the 18 voting members.

Although for some the debate is settled, others are not pleased. "We don't take a metre stick in Paris and add a foot-and-a-half to it," says Lucy Edwards, a marine geologist with the US Geological Survey in Reston, Virginia. "You can redefine it by being more precise, but you don't increase its size by 40%." Edwards has practical concerns as well: in the 1980s, the USGS reworked all of its maps and terminology to reflect the decision to place the Pleistocene at 1.8 million years ago. Now that the international standards have changed, it will have to do so again.

Marie-Pierre Aubry of Rutgers University in Piscataway, New Jersey, who lobbied against the change, says that the rules of science are being violated. Whereas other major boundaries in Earth's history are associated with faunal extinctions and turnover, she says, "you come to the Neogene–Quaternary boundary, and there is nothing there". She notes that the term Neogene, not Quaternary, is used widely in textbooks to describe the current period. The Neogene community has already responded by petitioning the IUGS to suspend the vote.

Others are moving on. "In the end, it is only a shift in nomenclature," says Martin Van Kranendonk, a geologist at the Geological Survey of Western Australia in East Perth, and one of the two voting members who voted against the Quaternary proposal. "The rocks and time itself haven't changed," he says. "It's just what we have chosen to call them."

No impact, Deccan volcanism killed the dinosaurs

So here we are again: back to Deccan volcanism as the culprit for dino extinctions.
Gerta Keller of Princeton University, based on fossil assemblages and the supposed age of the impact event has come to such a conclusion, in her paper with Theirry Adatte of Neuchatel Uni, Switzerland, the J Geol Soc London (April 27, 2009).

Read the TIME report by Jeffrey Kluger here


When a scientific principle is common knowledge even in grammar school, you know it has long since crossed the line from theory to established fact. That's the case with dinosaur extinction. Some 65 million years ago — as we've all come to know — an asteroid struck the earth, sending up a cloud that blocked the sun and cooled the planet. That, in turn, wiped out the dinosaurs and made way for the rise of mammals. The suddenness with which so many species vanished after that time always suggested a single cataclysmic event, and the 1978 discovery of a 112-mile, 65-million-year-old crater off the Yucatán Peninsula near the town of Chicxulub seemed to seal the deal.

Now, however, a study in the Journal of the Geological Society throws all that into question. The asteroid impact and dinosaur extinction, say the authors, may not have been simultaneous, instead occurring 300,000 years apart. That's an eyeblink in geologic time, but it's a relevant eyeblink all the same — one that occurred at just the right moment in ancient history to send the extinction theory entirely awry.

The controversial paper was written by geoscientists Gerta Keller of Princeton University and Thierry Addate of the University of Lausanne, in Switzerland. Both researchers knew that challenging the impact doctrine would not be easy. The asteroid charged with killing the dinosaurs, after all, left more than the Chicxulub crater as its calling card. At the same 65-million-year depth, the geologic record reveals that a thin layer of iridium was deposited pretty much everywhere in the world. Iridium is an element that's rare on Earth but common in asteroids, and a fine global dusting of the stuff is precisely what you'd expect to find if an asteroid struck the ground, vaporized on impact and eventually rained its remains back down. Below that iridium layer, the fossil record shows that a riot of species was thriving; above it, 65% of them went suddenly missing.

But Keller and Addate worried that we were misreading both the geologic and fossil records. They conducted surveys at numerous sites in Mexico, including a spot called El Peñón, near the impact crater. They were especially interested in a 30-ft. layer of sediment just above the iridium layer. That sediment, they calculate, was laid down at a rate of about 0.8 in. to 1.2 in. per thousand years, meaning that all 30 feet took 300,000 years to settle into place.

Analyzing the fossils at this small site, they counted 52 distinct species just below the iridium layer. Then they counted the species above it. The result: the same 52. It wasn't until they sampled 30 feet higher — and 300,000 years later — that they saw the die-offs.

"The mass extinction level can be seen above this interval," Keller says. "Not a single species went extinct as a result of the Chicxulub impact."

Keller's and Addate's species samplings are not, of course, conclusive, and plenty of other surveys since 1978 do tie the extinctions closely to the asteroid. But since the new digs were so close to ground zero, the immediate species loss ought to be have been — if anything — greater there than anywhere else in the world. Instead, the animals seemed to escape unharmed. Other paleontologists, however, believe that the very proximity of El Peñón to the impact site makes the results even less reliable. Earthquakes and tsunamis that resulted from the collision could have wrought havoc on the sedimentary record, causing discrete strata to swirl together and completely scrambling time lines. Keller disagrees, pointing out that the slow accretion of sediment that she and Addate recorded is completely inconsistent with a sudden event like a tsunami. (See pictures of animals in space.)

"The sandstone complex was not deposited over hours or days," she says. "Deposition occurred over a very long time period."

So if the Chicxulub asteroid didn't kill the dinosaurs, what did? Paleontologists have advanced all manner of other theories over the years, including the appearance of land bridges that allowed different species to migrate to different continents, bringing with them diseases to which native species hadn't developed immunity. Keller and Addate do not see any reason to stray so far from the prevailing model. Some kind of atmospheric haze might indeed have blocked the sun, making the planet too cold for the dinosaurs — it just didn't have to have come from an asteroid. Rather, they say, the source might have been massive volcanoes, like the ones that blew in the Deccan Traps in what is now India at just the right point in history.

For the dinosaurs that perished 65 million years ago, extinction was extinction and the precise cause was immaterial. But for the bipedal mammals who were allowed to rise once the big lizards were finally gone, it is a matter of enduring fascination.
[http://www.time.com/time/health/article/0,8599,1894225,00.html]

Diamonds in Tamil Nadu!!

Nature journal is skeptical about the report of microdiamonds from the Tamil Nadu coast, which was reported in Current Science. Read the Nature article.

Beach diamonds not for picking yet

All that glitters may not be diamond.All that glitters may not be diamond.

A recent report by geologists at Dr. H.S. Gour University at Sagar in Madhya Pradesh has raised a controversy: are the beaches of Tamilnadu in southeastern India really strewn with nuggets of diamond as these scientists claim?

A few days ago P. K. Kathal, his doctoral student M. K. Purohit and co-worker S. H. Adil announced that they have found 'micro-and macro-diamonds' in Nagapattinam and Vedaranyam beaches of Tamilnadu coast. These diamonds are so called because they are less than a millimeter in size. "A thorough search of the entire coast might yield larger diamonds," Kathal told Nature India and recommended detailed exploration of the entire Tamilnadu coast.

Their 'discovery' was reported in one of India's leading science journals1 with a photograph of the beach diamond on the cover page. That and a spate of media reports about the treasure on the sands may have already sent eager prospectors to the beaches with sieves in their hands.

But some geologists like Gopalakrishnarao Parthasarathy of the National Geophysical Research Institute in Hyderabad are skeptical about the find. "We have to make absolutely sure that what was discovered in the beaches is indeed diamond and not something else," he told Nature India.

Parthasarathy recalled that after the December 2004 Tsunami there were reports from the Geological Survey of India (GSI) of the occurrence of micro-diamonds in Kanyakumari beach. "It eventually proved to be zircon and not diamond," he said. "Zirconium silicate (or zircon) resembles diamond, and hence usually is mistaken for diamond."

Beaches usually are repositories of all products derived from the catchments of nearby rivers, coastal belt and continental region, including grains leaching from coastal rocks that contain heavy minerals like ilmenite, rutile, zircon, garnet, sillimanite and monazite.

In their study, the Sagar researchers collected sand samples from 16 beaches along the 2500-km coast from Puri to Kanyakumari. After filtration and wet-sieving to remove all the sand and heavy minerals, they hand-picked those grains showing brilliant luster.

According to the scientists, their study yielded 16 lustrous grains from Nagapattinam sample and 13 from Vedaranyam beaches.

"Normally, 6 grains of diamond per 100 grams of sediments is (considered a good) deposit," Purohit told Nature India. "In our case it is 13 to 16 grains, some of them bigger than one millimeter in size. This finding may lead to more (as well as) bigger diamonds in sediments in the area from Vedaranyam to Nagapattinam."
Map of Nagapattinam and Vedaranniyam beaches in the east coast of India from where the 'diamonds' were obtained.Map of Nagapattinam and Vedaranniyam beaches in the east coast of India from where the 'diamonds' were obtained.

"This is indeed a first report of micro- and macro-diamonds from the region with economic implications — a reason why the journal front-paged our paper," Purohit said.

But questions have been raised over the authenticity of the claims and also over the reported source of the beach diamonds.

According to the Sagar scientists, the beach grains were identified as micro- and macro-diamonds after visual examination using different types of microscopes. Kathal says examination a petrological microscope revealed their octahedron shape, brilliant (admandine) lustre, and 'isotropic' nature that are the very characteristic of diamonds. The morphological and optical characteristics of the beach grains combined with results of X-ray diffraction analysis confirm they are diamonds, Kathal said. "There should be no doubt on their identification."

However, according to Parthasarathy, an expert in characterization of minerals, while X-ray diffraction analysis is suitable for large crystalline diamonds, "laser Raman spectroscopy is the only method for unambiguous identification of micro-diamonds and practised by experimental scientists throughout the world."

From the size and shape of the recovered 'diamond' grains the scientists guess that they are released from a nearby kimberlite source. Kimberlites — 'plutonic' rocks that occur in the Earth's crust in vertical structures known as kimberlite pipes — are the most important source of mined diamonds today. According to Kathal an earlier study by the GSI in 2007 had indicated the presence of kimberlites in Mahboobnagar district of Andhra Pradesh suggesting that this may be the source of the bounty on Tamilnadu beaches.

"Nagapattinam and Vedaranyam fall in Godavari delta. Godavari has a very large basin," Kathal observed.

Parthasarathy, however points out the Mahboobnagar kimberlite is 'non-diamondiferous' and the only diamond bearing pipe is at Wajrakarur in Anathapur district of Andhra Pradesh. In any case, he says, there is no way these diamonds from Andhra Pradesh can be transported to Nagapattinam beach, by any normal geological or weathering processes. "To my knowledge there are no kimberlites in Tamilnadu or in Cauvery river zone" that could account for the presence of diamonds in the beach sands of Tamilnadu, he adds.
The 'diamonds' obtained from the beaches.The 'diamonds' obtained from the beaches.

Kathal says he never proclaimed that Mahboobnagar Kimberlite could have released the diamonds. "Our finding should rather be taken as an evidence of possible kimberlite pipe/pipes in the basin so that larger/more diamonds could be found in future," he said. The Sagar scientists, however, do not rule out the possibility that some of the recovered diamonds might have been introduced by extra-terrestrial objects like meteorites that fell on the Earth.

But S.V.S.Murty, chairman of the Planetary Sciences Division at Physical Research Laboratory (PRL) in Ahmedabad considers their extra-terrestrial nature highly unlikely.

"I am not commenting on the authenticity of identification of the grains as diamonds," he told Nature India. "I am only telling that (if they are indeed diamonds) they are certainly terrestrial in origin." The extra-terrestrial (meteoritic) diamonds, according to Murty, will be much smaller in size (nano-diamonds) than what the Sagar scientists claim to have discovered in the Tamilnadu beaches.

Parthasarathy suggests that the Sagar team "may have to contact some Raman spectrosocpist to confirm" that they have indeed discovered diamonds and also identify a more realistic origin of in the vicinity of where they were found.

Anxious prospectors should wait till then.

References
Purohit, M. K. et al. Discovery of micro-diamonds in beach sands of the Nagapattinam and Vedaranniyam beaches, southern east coast of India. Curr. Sci. 96, 767-768 (2009)