Reason of dinosaur extinction

The dinosaurs died gradually from climate change caused by a series of severe volcanic eruptions in India at the end of the Cretaceous period, says Gerta Keller, professor of geosciences at Princeton University. This theory contradicts the long-held notion that the dinosaurs died due to climate change when a giant meteor hit the Yucatan region of Mexico.

Keller's theory has not yet been adopted by the broader scientific community, but it is rapidly gaining traction as she and her colleagues, funded by the National Science Foundation, report findings from their field work in India and Mexico. The most significant finding is geologic evidence that the mass extinction and the impact of the giant meteor occurred at two different times.

"The Chicxulub impact hit the Yucatan about 300,000 years before the mass extinction that included the dinosaurs and therefore could not have caused it," Keller says. "We know the age of impact because my team discovered a layer of tiny glass melt-rock spherules in Mexico and Texas." The spherules formed when the rocks were vaporized by the impact and blown into the stratosphere--and then rained down over North and Central America. "This glass spherule layer marks the precise time of the impact 300,000 years ago," she notes.

The sediments and fossils in the older sediments below the spherule layer and younger sediments above it reveal how life was affected by the impact.

"We see no change, not a single species died out, so the mass extinction 300,000 years later must have been caused by another catastrophe," Keller says. She's firm in her belief that the other catastrophe was a series of volcanic eruptions in the Deccan Traps, a volcanic mountain range that covers much of India today. The mountains, which today are 12,000 feet high, were much higher in prehistoric times.

"Volcanic eruptions poured out lava flows after lava flows, stacking them like a layer cake," she says. "The total volume in cubic miles was greater than the Rockies and the Sierras combined."

Related research by volcanologists Vincent Courtillot, Steve Self, Mike Widdowson, and Anne Lise Chenet shows the lava eruptions were not continuous but occurred in pulses, with each pulse lasting about 10--to at most 100--years, and the pulses were separated by short time periods of quiescence. New results from eight subsurface cores drilled by the Oil and Gas Corporation of India in the Krishna-Godavari Basin of eastern India reveal that at least nine lava flows mark the critical volcanic phase that ended in the mass extinction. This ending phase may have occurred over as little as 10,000 to 100,000 years. For each lava eruption, fire shot in tall columns from fissures in the Earth's surface and lofted gases into the stratosphere while the oozing lava spread sheet-like, or in rivers, up to 650 miles across India, and formed the longest lava flows on Earth.

"Their destructive nature is evident in the marine life record, which decreased by about 50 percent after the first of these long lava flows," Keller said. "By the time of the last lava flow, the mass extinction was complete."

The sulfur dioxide gas injected into the stratosphere converted to sulfate aerosols that caused climate cooling. The cooling lasted until the sulfate aerosols washed out as acid rain and caused the ocean to acidify in the process.

Research on smaller and more recent eruptions, such as the Laki eruption of Iceland in 1783-1784, clarified for scientists the extreme climate effects of volcanic eruptions and the resulting death and destruction of humans, animals, plants and marine life. In spite of the widespread devastation caused by Laki, mass extinction did not occur. The more recent example of Mt. St. Helen's in Washington State has shown just how quickly a local ecosystem can come back after a volcanic eruption.

Then why did it take Earth's ecosystem half a million years to fully recover after the mass extinction that killed the dinosaurs?

"The answer seems to be the occurrence of at least four additional massive Deccan eruptions about 280,000 years after the mass extinction," Keller says. "After those final eruptions, Earth began a full recovery leading to the evolution of life as we know it."

Keller doesn't disagree with scientists who believe the Chicxulub impact affected climate. The event would certainly have caused earthquakes, tsunamis, regional fires and injected huge quantities of sulfur dioxide into the stratosphere, causing cooling and acidification of the land and oceans. "The difference is that the quantity of gas injection from the main phase of Deccan eruptions was 30 to 100 times larger than the Chicxulub impact and occurred over as little as 10,000 to 100,000 years, with each pulse lasting about 10 years or more."

Up until now, skeptics have doubted whether gas from Deccan-like eruptions reaches the stratosphere, but the relatively small 1783-1784 Laki eruption in Iceland revealed that even rather small eruptions loft gases into the stratosphere.

Until recently, it was also believed that the last phase of Deccan volcanic eruptions occurred over a million-year period, which would have been long enough for the environment to recover between eruptions, thus preventing a runaway extinction effect. Vincent Courtillot and collaborators from the Institut de Physique du Globe de Paris have recently discovered that the main phase of Deccan eruptions was much shorter and culminated near the Cretaceous-Tertiary boundary. Known as the "K-T boundary" to scientists, it marks the end of the Mesozoic Era and is associated with the mass extinction.

Most importantly, field work by Keller and her collaborators revealed that the mass extinction coincided with the end of the main phase of Deccan eruptions suggesting that volcanism is the "smoking gun" that killed the dinosaurs.

"These new discoveries have made the volcanism-mass extinction theory a very viable cause for the end-Cretaceous mass extinction," Keller says.

According to NSF Program Director Harold Lane: "Dr. Keller's recent NSF-supported research stokes continued debate about the cause of the near extinction of earth's biota at the end of the Cretaceous--a major event in the history of life on earth."

Keller and her collaborators will present talks and papers about their findings at the December 2008 AGU meeting in San Francisco. Their work will also be included in an upcoming History Channel feature titled What Really Killed the Dinosaurs.

Secrets and power of brain

The human brain is a three-pound paradox: We use it every moment of our lives, yet so much about our brains remains a mystery to us. How do our brains make decisions? Why is it so easy to remember the words to our favorite childhood song, but we forget important passwords? Can someone really read your thoughts?

Four leading neuroscientists and psychologists discussed these and other brain research questions at a forum held at the Franklin Institute in Philadelphia, Pa., last winter. More than 15 video clips from that event and other interviews with these experts are now available online. They describe how recent advances in science and technology are making it possible to unravel some of these mysteries while showing us just how complex our brains really are.

Award-winning author, blogger and Discover magazine columnist Carl Zimmer moderated the panel discussion which featured:

• Daniel J. Levitin, James McGill Professor of Psychology at McGill University and author of the bestselling book "Your Brain on Music";
• Michael Gazzaniga, director of the Sage Center for the Study of Mind at the University of California and author of the new book "Human: The Science Behind What Makes Us Unique";
• Rebecca Saxe, Carole Middleton Career Development Professor in the department of brain and cognitive sciences at MIT; and
• Samuel Wang, associate professor of neuroscience at Princeton University and author of "Welcome to Your Brain."

In addition to presenting insights from their work, the experts also provided a unique perspective on the advances being made in the field of neuroscience and the many exciting and challenging implications they hold. For example, if brain scans can tell whether a person is lying, or if types of violence and criminal behavior can be traced to specific abnormalities in the brain, what does that mean for our justice system? As Gazzaniga puts it in one of the videos, "Is neuroscience painting a picture of the nature of the human condition in such a way that concepts of punishment take on new meaning?"

Saxe takes this thought further by exploring what cutting-edge neuroscience can tell us about why ordinary people can participate in extraordinarily cruel behavior, like that put on display at the Abu Ghraib prison in Iraq.

The experts also challenge our common perceptions about how our brains work. Have a hard time making up your mind before you weigh all your options? It turns out, according to Wang, that your brain may have already made a decision without you knowing it, and all your deliberations are for naught. Wang also dispels the common myth that we only use 10 percent of our brains--we use almost all of it at some point.

Diet decides shape of teeth

Researchers at Johns Hopkins found that use over time and not just genetics informs the structure of jaw bones in human populations. The researchers say these findings may be used to predict the diet of an ancient population, even if little evidence exists in the fossil record. It can also make it easier for scientists to pinpoint the genetic relationship between fossils.

heir results were published online June 23 in the American Journal of Physical Anthropology.

"Our research aimed to see how much of the mandible's—or jaw bone's—shape is plastic, a response to environmental influences, such as diet, and how much is genetic. We used archaeological jaw bones from two different regions to answer that question," explains Megan Holmes, graduate student at the Johns Hopkins Center for Functional Anatomy and Evolution, and lead author of the paper. "Before we can make inferences about what the shape of a bone tells us, like what environment the individual lived in, who it's related to or what it ate, we have to understand what creates that shape. The idea that function influences the shape of jaw bones is great for the archeological record in terms of discovering the diet of a population, and it's also really useful for reconstructing the fossil record—finding which fossils are related to which, and how."

The group chose to study the Arikara and Point Hope American Indian populations, since they were genetically isolated from other groups and ate different diets. They investigated bones from the regions dating back to the 1600s and 1700s, times for which the diets are known from other records. The Point Hope population in Alaska ate a "hard" diet that included tough dried meat. They also used their teeth for a variety of nonfood-related tasks, such as stripping leather. The Arikara, from the Dakota area of the United States, ate a softer diet, which consisted of farming supplemented with light hunting.

The researchers precisely measured jaw bones from 63 members of the Point Hope population and 42 individuals from the Arikara population using an X-ray gun as well as calipers, and they used those measurements to extrapolate the proportions of the entire jaw. "The jaw bones were similar in children before they were old enough to start chewing, but different in adulthood, which implies that this divergence is likely a functional result of their diet and the use of their jaw, rather than genetics," says Holmes.

The changes to the jaw bones were explained using a theory drawn from engineering, which directly relates the geometry of a bone to the stresses put on it during use. The team was able to investigate very specific parts of the jaw bones and relate them to specific dietary habits. In the Point Hope population, for example, they found round, wide jaw bones—a result of having to exert more force to chew a harder diet. The Arikara, on the other hand, did not show this expansion, which they attributed to the lighter chewing requirement of a softer diet.

"Genetics creates a blueprint of the bone, but a lot of things influence the bone's construction," says Holmes. "Mechanical pressure from muscle stress and strain from day-to-day activities can remodel the bone's surface and internal structure. Knowing how much the shape of a mandible we find is related to diet and how much genetically connects it to fossils found elsewhere can really help us parse out the family tree."

Source : Johns Hopkins Medical Institutions