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Blobrana


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RE: Dinosaur extinction
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New research into a missing link in climatology shows that the Earth was not overcome by a greenhouse period when dinosaurs dominated, but experienced rapid fluctuations in temperature and sea level change that resulted in a balance of the global carbon cycle. The study is being published in the March issue of Geology.

"Most people think the mid-Cretaceous period was a super-greenhouse. But in fact it was not too dissimilar to the climates over the past 5 million years" - Darren Gröcke, assistant professor and Director of the Stable Isotope Biogeochemistry Laboratory at McMaster University.

By using high-resolution stable-isotope analysis from 95-million-year-old fossilized wood collected from Nebraska, Gröcke and his team were able to precisely correlate the terrestrial carbon cycle with that from deep-sea records. However, when they compared the carbon curves from both records, it was evident that a chunk of about 500,000 years was missing from the terrestrial record. Other records already indicated a drop in sea level, a 2-4ºC drop in oceanic temperature and a breakdown in oceanic stratification coincident with a marine extinction event.

"Rapid, large falls in sea-level in the ancient record are typically only produced by a glaciation, and so the combination of all the data during the mid-Cretaceous period suggests a short-lived glaciation during a period generally considered to be a super-greenhouse. Whatever hits the water causes a ripple effect on land. Earth often undergoes rapid temperature fluctuations, and this new information may help us to understand how the biosphere will respond to human-generated alterations of CO2 concentration" - Darren Gröcke.

He said the research not only challenges conventional wisdom surrounding ancient climates, it makes a case for the use of high-resolution sampling in order to reconstruct a more accurate picture of the ancient climate and its affect on the Earth.

Source: McMaster University

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Blobrana


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The giant impact that shook the Earth 65 million years ago is still sending out shock waves, triggering a scientific feud over whether the event really killed off the dinosaurs.
Efforts to identify what wiped out the great creatures have been confused by evidence of massive volcanic activity in India at the same time, and a fossil record that suggests the dinosaurs disappeared gradually as the Earth's climate and geology changed over millions of years.

Now a bitter row has broken out on CCNet, a scholarly electronic network, over a paper by Peter Schulte of the Universität Erlangen-Nürnberg and colleagues in the journal Sedimentary Geology: they conclude that two cores drilled in Brazos, Texas, provide new support for the much-loved disaster movie scenario.
With Robert Speijer, Hartmut Mai and Agnes Kontny, Mr Schulte concludes that the evidence is "unequivocal" that debris and "ejecta" sent out by the impact coincides with the timing of the mass extinction.
Their work is the latest to back a remarkable hypothesis proposed in 1980 by the American father-and-son team Profs Luis and Walter Alvarez, who came to a cataclysmic conclusion after studying a thin layer of dirty sulphurous clay in Gubbio, Italy.
This clay marked what scientists call the K-T boundary, the junction between rocks in which the fossils of dinosaurs are found, and those above, in which dinosaur bones have been replaced by more modern creatures.
From the chemistry of the clay, the Alvarezes deduced that there had been a giant impact 65 million years ago, now called the Chicxulub impact.

The new paper, says the German team, "provides no evidence that Chicxulub predated the K-P (K-T) boundary and allows for unequivocal positioning of the K-P (K-T) boundary at the event deposit".
Not so, say detractors on CCNet. Prof Gerta Keller of Princeton University accused the team of "ignoring scientific methods", making claims with "no basis in fact" and "circular reasoning" by assuming a K-T age for the Chicxulub impact when this age is in doubt and predates the mass extinction.

Another detractor, from Utrecht University, denounced their "firm conclusions claiming 'unequivocal' certainty".
Though common wisdom among many scientists favours an asteroid strike ending the age of dinosaurs, one group of scientists remains doggedly undecided about this vision of apocalypse: dinosaur experts.

"There is absolutely no consensus as to whether there was a sole cause and what it was. The feud does not involve people who work on dinosaurs, but sedimentologists and hard rock geologists" - Angela Milner, of the Natural History Museum, London.

The only thing that everyone can agree on is that the dinosaurs became extinct.


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Blobrana


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Cretaceous period
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Kirk Johnson swung his pickaxe against the base of Pulpit Rock and broke off a football-sized chunk resembling a piece of cake thinly layered with light and dark chocolate.

A gentle whack against its side split it open to reveal a perfectly preserved, three-pointed, prehistoric tree leaf the size of a man's hand.
"Look at this,'' Johnson said excitedly to project manager Beth Ellis and geologist Bob Raynolds, his team of fossil prospectors from the Denver Museum of Nature & Science. "This is a really nice one; maybe the best we've found yet''
During a three-day dig, the team gathered dozens of similar fossils from Pulpit Rock and at an outcropping along nearby Rusina Road. The two sites are among many in the area that Johnson, chief curator of paleontology at the museum, and other scientists visit in their quest to reconstruct life through the ages.

"Colorado Springs is one of the best places in the world to see the history of the Earth,'' Johnson said, because of its exposed or easily excavated prehistoric molten rock and caches of volcanic ash, mud and sand.

He started studying the rock under Colorado Springs in 1991 and intensified efforts in recent years because of the wealth of fossils and the access to many layers of rock offered by the region's topography.

"We are trying to build the geology of the Rocky Mountains as of 65 million years ago. We are trying to understand how the landscape changed and reconstruct the Rocky Mountains'' - Kirk Johnson.

Eventually, Johnson and his team will publish their findings in news articles and scientific journals, use results of their research to update museum exhibits and include it in future lectures. But that will take a while.

"We take a bag of leaves and can tell what the forest looked like. We'll dig up 400 or 500 leaves and study them''- Kirk Johnson.

The leaves gathered last week will help him determine whether the landscape was arid or a rainforest or made up of conifers and pine trees - at least, ancient predecessors of today's tree species.

"We're looking here at a whole suite of leaves that are previously undiscovered and undescribed. We've found a couple kinds of conifers and a couple of ferns and broadleafs. But exactly what they are, we don't know''- Kirk Johnson.

The one thing he is sure of is that the leaves were between 65.5 million and 68 million years old.

Johnson thinks the latest leaf lived on a tree during the Cretaceous period — a time when the 5-ton Tyrannosaurus rex lumbered to the top of the food chain and the lush forest also was home to the plant-eating Triceratops, as well as other dinosaurs, birds, mammals and other organisms.

The evidence is buried within Pulpit Rock, a spired outcropping of white, layered sandstone that rises near Interstate 25.

More than just a striking landmark, Pulpit Rock has survived 10 million years of erosion by Monument Creek - erosion that also unearthed and created the world-famous rock formations in Garden of the Gods, the hogbacks of Red Rock Canyon and hoodoos throughout the area.

Pulpit Rock is a vault, of sorts, where Mother Nature stored fossil clues - like the leaves, as well as dinosaur bones, volcanic ash pits and even grains of pollen - for scientists like Johnson to use.
In most places on Earth, these vaults remain deep underground. They are accessible around the Springs because of a dramatic uplift about 68 million years ago that created Pikes Peak and the Front Range.
The uplift was so powerful that it thrust up tons of granite to create the 14,115-foot mountain. Elsewhere, you have to dig 14,000 feet below the surface to find Pikes Peak-type granite.
The uplift also bent and pushed to the surface layers of rock formations that define each era spanning 500 million years. Those layers have been exposed by erosion from wind and water, and scientists now mine them for clues to the past.

Perhaps the most important clue is a centimetre-thick layer of clay, laced with unique space dust called iridium.

Scientists generally believe an asteroid the size of the Air Force Academy smashed into Mexico's Yucatan Peninsula - a violent collision that incinerated the atmosphere and caused an eruption of ash that blanketed the globe, wiping out most plant and animal life on Earth, including the dinosaurs.
The ash - with its space dust, crystals and soot from global fires - eventually compressed into the layer of clay that lies buried beneath 65.5 million years of sedimentary rock.
It separates two distinct periods of time on Earth - the Cretaceous, when dinosaurs lived and became extinct, and the Tertiary, which gave rise to the age of mammals.
The thin layer of clay is known as the K/T boundary (K for the German spelling of Cretaceous and T for Tertiary) and some think it runs throughout Colorado Springs.

"The boundary is so important because it is a precise marker in geologic time'' - Kirk Johnson.

So prospecting above and below the boundary allows scientists to more accurately date their fossils and reconstruct life.
It's not a high-tech exercise. The leaves collected in the sun and heat were wrapped in toilet paper, placed in cardboard boxes and taken back to the museum for study.

source

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Blobrana


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Posts: 131433
Date:
Dinosaur extinction
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A spider relative called a harvestman trapped in amber could shed light on how arachnids were affected by the extinction that wiped out dinosaurs.
The 100 million-year-old arachnid, which looks like it might have died last year, wandered though a dinosaur-dominated world.
Though older fossils exist, hardly any are known from the Mesozoic Era (245 million-65 million years ago).
Details appear in Proceedings of the Royal Society B journal.



"This specimen came from the Mesozoic Era, so basically the same time as the dinosaurs and generally there are very few fossil arachnids from this period. If you go back to the period of about 300 million-400 million years ago you actually have more arachnid fossils. So the fact that we have any harvestmen from this time period is really quite unusual." - Jason Dunlop, co-author, Museum für Naturkunde in Berlin.
Harvestmen are small arachnids related to spiders with very long, thin legs and a small body.
One of the reasons this specimen is causing excitement is that it might help tackle the question of how many arachnids groups managed to survive the great extinction of around 65m years ago.
This is thought to have been caused by an asteroid strike at the end of the Cretaceous Period, throwing up dust that blocked sunlight and dragged down temperatures globally.
If a fossil from the Mesozoic Era belongs to a family that existed in more modern times, its lineage must have made it through the extinction.
Although this particular harvestman cannot be included in modern groups it is pretty similar to later, post-extinction, specimens. This could mean that its lineage survived the catastrophe - and if it did, then it is likely that others did too.
"You have a fossil of 100 million years ago and at the end of the Cretaceous Period, about 65 million years ago, you have the end of the dinosaurs and the supposed mass extinction of all these animals…So this amber specimen gives us the first chance to really ask, did this effect creepy crawlies as well? …We can't put this in exactly a modern group but if you look at much younger ambers from maybe 40 million years ago, those are even more like modern ones." - Jason Dunlop.
"Whenever you find an arachnid from the Mesozoic Era, you can nearly always place it in a modern family. This means there may well have been extinctions of species, but overall the arachnids seem to have sailed through." - Paul Seldon, an arachnid expert from the University of Manchester, agrees the harvestamn adds another brick in the wall of evidence.



The leggy creature probably led life in quite a similar way to its modern successors.
Unlike true spiders, which are predators, harvestmen have broader tastes. They eat vegetable matter, dead insects and reportedly even enjoy dining on the odd bird dropping.
The harvestman hit on a successful evolutionary "design" fairly early on and has changed rather little over the past few hundred million years.
"We think they would have lived a similar life to modern harvestmen. If you go back to a very, very ancient fossil and look at the internal organs you see it actually has reproductive organs just the same as a living one, it has a breathing system the same as a living one - so it looks like there hasn't been any major change in the body plan." - Dr Dunlop.


-- Edited by Blobrana at 14:38, 2005-05-18

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