Scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have pinpointed the date of the dinosaurs’ extinction more precisely than ever thanks to refinements to a common technique for dating rocks and fossils. 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. Renne and his colleagues in Berkeley and in the Netherlands now have lowered this uncertainty to 0. 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 Renne noted that the greater precision matters little for recent events, such as the emergence of human ancestors in Africa 6 million years ago, because the uncertainty is only a few tens of thousands of years. One major implication of the revision involves the formation of meteorites, planetessimals and planets in the early solar system, he said.
All rights reserved. New insights about the asteroid thought to have killed off the dinosaurs suggest it may have just been the final blow, and that the reptiles were already suffering from a finicky climate prompted by volcanic eruptions long before the meteorite struck. The research, detailed in the February 8 issue of the journal Science , adds to the ongoing scientific debate over what exactly killed off the dinosaurs. That debate, which once revolved around the question of whether the culprit was an asteroid or volcano-induced climate changes, has evolved to consider the possibility that perhaps multiple environmental factors were involved.
Using a high-precision dating technique on tektites—pebble-sized rocks formed during meteorite impacts—from Haiti that were created during the event, the team concluded that the impact occurred 66,, years ago—slightly later than previously thought. When error limits are taken into account, the new date is the same as the date of the extinction, the team says, making the events simultaneous.
AGE LIMITATIONS ON THE K-T BOUNDARY IN NEW JERSEY The precise Owens and Sohl () used potassium-argon dating on the glauconites, and.
The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance. This layer was found many places around the globe and came to be associated with the boundary between the Cretaceous and Tertiary Periods, referred to as the K-T Boundary on the geological age scale.
The fact that a layer like this has been found at several locations scattered around the world suggests a large-scale atmospheric suspension of the material, such as would occur upon the impact of a sizable asteroid. Coupled with the presence of dinosaur fossils below this layer, but not above, this evidence has led to the asteroid model for the extinction of the dinosaurs.
This cross-section of the strata containing the iridium-rich layer is on display at the Smithsonian Museum of Natural History. The thickness of the layer appeared to be cm. Iridium-Rich Layer The element iridium was brought into the public view with the discovery of a subsurface layer which was greatly enriched in iridium compared with its normal abundance. Index Frankel, “The End of the Dinosaurs”.
Refining the date of the K/T boundary and the dinosaur extinction
According to abundant geological evidence, an asteroid roughly 10 km 6 miles across hit Earth about 65 million years ago. This impact made a huge explosion and a crater about km roughly miles across. Many asteroids of this type are now known; their orbits pass through the inner solar system and cross Earth’s orbit.
As a result, recent scientific papers refer to the K-T boundary as the K-Pg boundary. Dating the K-T Boundary. The date of the K-T (or K-Pg) boundary has also.
The Cretaceous—Paleogene K—Pg boundary , formerly known as the Cretaceous—Tertiary K-T boundary , [a] is a geological signature , usually a thin band of rock. K , the first letter of the German word Kreide chalk , is the traditional abbreviation for the Cretaceous Period and Pg is the abbreviation for the Paleogene Period. Its age is usually estimated at around 66 Ma million years ago ,  with radiometric dating yielding a more precise age of The K—Pg boundary is associated with the Cretaceous—Paleogene extinction event , a mass extinction which destroyed a majority of the world’s Mesozoic species, including all dinosaurs except for birds.
Strong evidence exists that the extinction coincided with a large meteorite impact at the Chicxulub crater and the generally accepted scientific theory is that this impact triggered the extinction event. In , a team of researchers consisting of Nobel Prize -winning physicist Luis Alvarez , his son, geologist Walter Alvarez , and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the K—Pg boundary contain a concentration of iridium many times greater than normal 30 times the average crustal content in Italy and times at Stevns on the Danish island of Zealand.
As iridium remains are abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K—Pg boundary. Shocked quartz granules and tektite glass spherules, indicative of an impact event, are also common in the K—Pg boundary, especially in deposits from around the Caribbean. All of these constituents are embedded in a layer of clay, which the Alvarez team interpreted as the debris spread all over the world by the impact. Using estimates of the total amount of iridium in the K—Pg layer, and assuming that the asteroid contained the normal percentage of iridium found in chondrites , the Alvarez team went on to calculate the size of the asteroid.
One of the consequences of such an impact is a dust cloud which would block sunlight and inhibit photosynthesis for a few years.
The Impact That Wiped Out the Dinosaurs
If you watched for an hour or two, the star would have seemed to grow in brightness, although it barely moved. Sixty hours later, the asteroid hit. The air in front was compressed and violently heated, and it blasted a hole through the atmosphere, generating a supersonic shock wave.
40Ar/39Ar dating of tektites discovered recently in Cretaceous-Tertiary (K-T) boundary marine sedimentary rocks on Haiti indicates that the K-T boundary and.
Scientists determine most precise dates yet for dinosaur extinction 66 million years ago. Rock strata in northeastern Montana; they span the time of the dinosaur extinction. This material is available primarily for archival purposes. Telephone numbers or other contact information may be out of date; please see current contact information at media contacts.
In an attempt to resolve the issue, scientists at the Berkeley Geochronology Center BGC at the University of California, Berkeley, and at universities in the Netherlands and the United Kingdom, have determined that an impact event occurred at about the same time as the mass extinction of the dinosaurs. Using a recalibrated technique for dating Earth minerals, the researchers hypothesize that impact happened 66,, years ago, and that it produced the final atmospheric conditions needed to wipe out the dinosaurs.
The newly determined date of the impact is the same, within error limits, as the date for the mass extinction event, which also occurred about 66 million years ago, according to Paul Renne, BGC director. The dates are so close, the researchers say, that it was likely that a comet or asteroid that, if not wholly responsible for the global extinction, at least dealt the death blow. But it probably wasn’t just the impact. The revised date clears up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures, Renne said.
Renne decided to recalculate the date of the boundary between the Cretaceous and Tertiary periods–the KT boundary–after recalibrating the argon-argon method used to date rocks, which relies on the decay rate of a radioactive isotope of potassium. The impact in question left a mile-wide crater in the Caribbean off the Yucatan coast of Mexico. Called Chicxulub cheek’-she-loob , the crater was excavated by an object some six miles across.
CHICXULUB: THE IMPACT CONTROVERSY
Plants and the K—T Boundary. Its impact on plant life appears to have been of a much lesser magnitude. The authors, both on the staff of the Denver Museum of Nature and Science, have published extensively on fossil plants of Tertiary and Cretaceous age. Nichols has been mainly concerned with the palynology the microfossil record , while Johnson has concentrated on leaf assemblages megafossils of this age span. The Alvarez father-and-son team argued that the cause of the peak occurrence of that element was the result of the impact of an extra-terrestrial body.
The diverse and disastrous consequences of such an impact were, they claimed, the most likely cause for the extinctions occurring at the close of the Cretaceous Period the K—T boundary.
Rare-earth-element diagram of K-T boundary interval rocks from North been collected for K-Ar dating (J.D. Obradovich, oral commun., ). It is clear that an.
Both were vilified and ostracized by the increasingly vocal group of impact hypothesis supporters. The Cretaceous-Tertiary boundary KTB mass extinction is primarily known for the demise of the dinosaurs, the Chicxulub impact, and the frequently rancorous thirty years-old controversy over the cause of this mass extinction. In a perverse twist of fate, this discovery also began the decline of this hypothesis, because for the first time it could be tested directly based on the impact crater and impact ejecta in sediments throughout the Caribbean, Central America and North America.
In that introduction, Keller et al. The discovery of similar anomalies elsewhere and the proposition that these anomalies and the KT extinctions resulted from the impact of a large extraterrestrial bolide have spurred over a decade of unparalleled research on the physical and biological events at and near the KT boundary. Chicxulub had become the KTB impact crater. This foregone conclusion only lacked the evidence.
A frantic hunt for confirmation of the KTB age of the Chicxulub impact crater had begun.
PHYSICAL STRATIGRAPHY OF K-T BOUNDARY STRATA
You’ve read 1 of 2 free monthly articles. Learn More. B uilt upon the slopes of Mount Ingino in Umbria, the ancient town of Gubbio boasts many well-preserved structures that document its glorious history.
that dated to the boundary between the Cretaceous and Tertiary periods—the so-called KT boundary—when the dinosaurs disappeared.
Detection of a new form of carbon in volcanic rock samples from Anjar town in Gujarat in western India has revived the debate on what killed the dinosaurs. Dinosaurs and almost 80 per cent of Earth’s other organisms were wiped out 65 million ears ago at the so-called K-T boundary KTB that marks the end of Cretaceous K , and beginning of Tertiary T periods in the geological calendar. Some say it was the result of extraterrestrial objects hitting the earth, a theory originally proposed by the Nobel physicist Luis Alvarez.
Others blame it on vast clouds of climate-altering gases released by eruptions that buried western India under layer upon layer of basaltic lava flows nearly 3, meters thick. Now, researchers from India’s three national laboratories have joined the fray. They report that their discovery of a new phase of fullerene or Carbon in the Anjar sedimentary rocks bolsters the impact theory.
According to this theory, a meteorite the size of a small city that landed in Chicxulub in Mexico 65 million years ago, coinciding with KTB, kicked up so much dust that it caused a global blackout triggering mass extinction. The key evidence of impact, besides the crater, is the abnormally high concentration of element Iridium found at K—T boundaries across the world. Iridium is more abundant in meteorites than in Earth’s crust and so it was hypothesized that the meteorite vaporized after crashing into Mexico and spread the Iridium into the atmosphere.
Since Alvarez and his team proposed the impact hypothesis in , over one hundred KTB sections have been identified worldwide based on the presence of anomalously high Iridium. The Anjar volcano-sedimentary sequence located in the Kutch region of Gujarat consists of nine lava flows covering a time span from
All available evidence is consistent with an impact into oceanic crust terminating the Cretaceous Period. The commonly cited evidence for a large impact stems from delicate clay layers and their components and the impact site has not yet been found. Impact sites have been suggested all over the globe. The impact is felt to have occurred near North America by: the occurrence of a 2 cm thick ejecta layer only at North American locales, the global variation of shocked quartz grain sizes peaking in North America, the global variation of spinel compositions with most refractory compositions occurring in samples from the Pacific region and possibly uniquely severe plant extinctions in the North American region.
Impact wave deposits have not been found elsewhere on the globe, suggesting the impact occurred between North and South America. Subsequent tectonism has complicated the picture.
The K-T Boundary had been placed at 65 million years in the past by potassium-argon and other geologic dating processes. The association of the Chicxulub.
Was it a comet or asteroid impact? Volcanic eruptions? Climate change? In an attempt to resolve the issue, an international team of scientists have determined the most precise dates yet for the dinosaur extinction 66 million years ago and for the well-known impact that occurred around the same time. The new extinction date is precise to within 11, years.
The revised dates clear up lingering confusion over whether the impact actually occurred before or after the extinction, which was characterized by the almost overnight disappearance from the fossil record of land-based dinosaurs and many ocean creatures. The new date for the impact — 66,, years ago — is the same within error limits as the date of the extinction, said Renne, making the events simultaneous. Argon-argon dating uses a mass spectrometer to measure the ratio of radioactive potassium in a sample of rock to its decay product, argon.
The amount of argon in a sample allows researchers to use rocks as incredibly slow clocks. Many people think precision is just about adding another decimal place to a number, but it’s far more exciting than that. It’s more like getting a sharper lens on a camera. It allows us to dissect the geological record at greater resolution and piece together the sequence of Earth history.