Showing posts with label Extinction. Show all posts
Showing posts with label Extinction. Show all posts

Friday, January 28, 2011

Dinosaurs Survived 700,000 Years After Mass Extinction



Science Daily: Dinosaurs Survived Mass Extinction by 700,000 Years, Fossil Find Suggests.

ScienceDaily (Jan. 28, 2011) — University of Alberta researchers determined that a fossilized dinosaur bone found in New Mexico confounds the long established paradigm that the age of dinosaurs ended between 65.5 and 66 million years ago.

The U of A team, led by Larry Heaman from the Department of Earth and Atmospheric Sciences, determined the femur bone of a hadrosaur as being only 64.8 million years old. That means this particular plant eater was alive about 700,000 years after the mass extinction event many paleontologists believe wiped all non-avian dinosaurs off the face of earth, forever.

Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats. Living bone contains very low levels of uranium but during fossilization (typically less than 1000 years after death) bone is enriched in elements like uranium. The uranium atoms in bone decay spontaneously to lead over time and once fossilization is complete the uranium-lead clock starts ticking. The isotopic composition of lead determined in the hadrosaur's femur bone is therefore a measure of its absolute age.

Thursday, February 19, 2009

The Extinction of the Woolly Mammoth



Some people have suggested that no woolly mammoths could have survived the Younger Dryas impact events.

However, this view has been conclusively demonstrated to be erroneous: The latest woolly mammoths (Mammuthus primigenius Blumenbach) in Europe and Asia: a review of the current evidence.

During the Last Cold Stage, woolly mammoths ranged very widely across Northern Eurasia into North America, but then disappeared as part of the global phenomenon of Late Quaternary megafaunal extinction. The timing and causes of this highly significant event have generated conflicting opinions and much debate. However, the overriding need is for more data, and recent years have seen the accumulation of significant new finds and radiocarbon dating evidence. In particular, research is currently focussing on the geographical pattern of extirpation leading to final extinction, rather than seeking a single ‘last appearance datum’. This Viewpoint article was commissioned by the Editor-in-Chief and is published following the paper by Lõugas et al. (Dating the extinction of European mammoths: new evidence from Estonia. Quat. Sci. Rev. 21 (2002) 1347) to place their finding in a wider context. We give a brief review of the youngest directly dated mammoth remains from different regions of Eurasia, based both on published sources and on our own current research. This includes a very important new record from Cherepovets, North Russian Plain, which together with the new date from Puurmani, Estonia indicates the persistence of mammoth in this region close to the Pleistocene–Holocene boundary. These and other records suggest that the previous picture of mammoths widespread before 12,000 ka BP (uncalibrated radiocarbon years ago), then restricted to limited areas of northern Siberia, although correct in outline, has important exceptions which modify our understanding of mammoth extinction.

Despite the many available radiocarbon dates for Eurasian mammoth relative to other extinct megafauna, it is apparent that much more work is needed. Only then can we adequately tackle the important question of the cause or causes of extinction
It seems some woolly mammoths did in fact survive.

Live Science: Surviving Extinction: Where Woolly Mammoths Endured.

Like an Ice Age version of Land of the Lost, a group of woolly mammoths survived mass extinctions on their own island hideaway.

The majority of mammoths died out about 11,000 years ago, at the end of the Pleistocene era. But on St. Paul Island, one of the Pribolofs 300 miles off the Alaskan coast, a small number of the six-ton behemoths apparently lasted an extra 3,000 years
.

Such resilient populations have been discovered on other continents, but this is the first evidence of mammoths outlasting the Pleistocene in North America. R. Dale Guthrie from the University of Alaska Fairbanks studied radiocarbon dating of fossil remains and showed that the mammoths were on St. Paul 7,908 years ago.

"With the present data, the idea isn't very controversial, but more data may show they lasted a little longer on the island than my one date," Guthrie told LiveScience.
And not only that, some woolly mammoths survived until the Bronze Age.

Radiocarbon: Radiocarbon Dating Evidence for Mammoths on Wrangel Island, Arctic Ocean, until 2000 BC.