Asteroid Killed Off the Dinosaurs, Says International Scientific Panel

The Cretaceous-Tertiary mass extinction, which wiped out the dinosaurs and more than half of species on Earth, was caused by an asteroid colliding with Earth and not massive volcanic activity, according to a comprehensive review of all the available evidence, published in the journal Science.

A panel of 41 international experts, including UK researchers from Imperial College London, the University of Cambridge, University College London and the Open University, reviewed 20 years' worth of research to determine the cause of the Cretaceous-Tertiary (KT) extinction, which happened around 65 million years ago. The extinction wiped out more than half of all species on the planet, including the dinosaurs, bird-like pterosaurs and large marine reptiles, clearing the way for mammals to become the dominant species on Earth.

The new review of the evidence shows that the extinction was caused by a massive asteroid slamming into Earth at Chicxulub (pronounced chick-shoo-loob) in Mexico. The asteroid, which was around 15 kilometres wide, is believed to have hit Earth with a force one billion times more powerful than the atomic bomb at Hiroshima. It would have blasted material at high velocity into the atmosphere, triggering a chain of events that caused a global winter, wiping out much of life on Earth in a matter of days.

Scientists have previously argued about whether the extinction was caused by the asteroid or by volcanic activity in the Deccan Traps in India, where there were a series of super volcanic eruptions that lasted approximately 1.5 million years. These eruptions spewed 1,100,000 km3 of basalt lava across the Deccan Traps, which would have been enough to fill the Black Sea twice, and were thought to have caused a cooling of the atmosphere and acid rain on a global scale.

In the new study, scientists analysed the work of palaeontologists, geochemists, climate modellers, geophysicists and sedimentologists who have been collecting evidence about the KT extinction over the last 20 years. Geological records show that the event that triggered the extinction destroyed marine and land ecosystems rapidly, according to the researchers, who conclude that the Chicxulub asteroid impact is the only plausible explanation for this.

Despite evidence for relatively active volcanism in Deccan Traps at the time, marine and land ecosystems showed only minor changes within the 500,000 years before the time of the KT extinction. Furthermore, computer models and observational data suggest that the release of gases such as sulphur into the atmosphere after each volcanic eruption in the Deccan Traps would have had a short lived effect on the planet. These would not cause enough damage to create a rapid mass extinction of land and marine species.

Dr Joanna Morgan, co-author of the review from the Department of Earth Science and Engineering at Imperial College London, said: "We now have great confidence that an asteroid was the cause of the KT extinction. This triggered large-scale fires, earthquakes measuring more than 10 on the Richter scale, and continental landslides, which created tsunamis. However, the final nail in the coffin for the dinosaurs happened when blasted material was ejected at high velocity into the atmosphere. This shrouded the planet in darkness and caused a global winter, killing off many species that couldn't adapt to this hellish environment."

Dr Gareth Collins, Natural Environment Research Council Fellow and another co-author from the Department of Earth Science and Engineering at Imperial College London, added: "The asteroid was about the size of the Isle of Wight and hit Earth 20 times faster than a speeding bullet. The explosion of hot rock and gas would have looked like a huge ball of fire on the horizon, grilling any living creature in the immediate vicinity that couldn't find shelter. Ironically, while this hellish day signalled the end of the 160 million year reign of the dinosaurs, it turned out to be a great day for mammals, who had lived in the shadow of the dinosaurs prior to this event. The KT extinction was a pivotal moment in Earth's history, which ultimately paved the way for humans to become the dominant species on Earth."

In the review, the panel sifted through past studies to analyse the evidence that linked the asteroid impact and volcanic activity with the KT extinction. One key piece of evidence was the abundance of iridium in geological samples around the world from the time of the extinction. Iridium is very rare in Earth's crust and very common in asteroids. Immediately after the iridium layer, there is a dramatic decline in fossil abundance and species, indicating that the KT extinction followed very soon after the asteroid hit.

Another direct link between the asteroid impact and the extinction is evidence of 'shocked' quartz in geological records. Quartz is shocked when hit very quickly by a massive force and these minerals are only found at nuclear explosion sites and at meteorite impacts sites. The team say that an abundance of shocked quartz in rock layers all around the world at the KT boundary lends further weight to their conclusions that a massive meteorite impact happened at the time of the mass extinction.

The panel was able to discount previous studies that suggested that the Chicxulub impact occurred 300,000 years prior to the KT extinction. The researchers say that these studies had misinterpreted geological data that was gathered close to the Chicxulub impact site. This is because the rocks close to the impact zone underwent complex geological processes after the initial asteroid collision, which made it difficult to interpret the data correctly.

Choking Is a Leading Cause of Injury and Death Among Children

 

Choking is a leading cause of injury and death among children, especially those younger than 4 years of age. The majority of choking-related incidents among children are associated with food, coins and toys. A new policy statement from the American Academy of Pediatrics (AAP), led by a doctor at Nationwide Children’s Hospital and published in the February 22 online issue of Pediatrics, takes a closer look at preventing choking among children.

On average, a child will die every 5 days in the United States from choking on food. However, too little attention is paid by government agencies and food manufacturers to minimizing choking risks. Although some food manufacturers voluntarily place warning labels on high risk products, more work needs to be done to implement safety standards for all high risk foods in regard to choking.

“We have laws and regulations in this country that require warning labels to be placed on toys that pose choking hazards, and we have systems that monitor and recall consumer products that pose a risk,” said the policy’s lead author Gary Smith, MD, DrPH, director of the Center for Injury Research and Policy at Nationwide Children’s Hospital. “However, there are no such regulations on high risk foods - and children are much more likely to put food in their mouths than a toy.”

According to the policy statement, the AAP recommends:

• Warning labels on foods that pose a high choking risk
• A recall of food products that pose a significant choking hazard
• The establishment of a nationwide food-related choking-incident surveillance and reporting system
• A commitment from food manufacturers to design new food and redesign existing food to minimize choking risk, to the extent possible

Parents and caregivers should also be made aware of foods that could be choking hazards. The risk of choking depends on the shape, size and consistency of the item, along with the developmental and behavioral capabilities of the child. Many foods that are thought to be “kid friendly” are actually dangerous. Foods like grapes, popcorn and nuts can easily become lodged in a young child’s throat or lungs. Hot dogs pose the greatest risk, as they cause more choking deaths than any other food.

“If you were to design the perfect plug for a child’s airway, you couldn’t do much better than a hot dog,” said Dr. Smith, also a Professor of Pediatrics at The Ohio State University College of Medicine. “It will wedge itself in tightly and completely block the airway, causing the child to die within minutes because of lack of oxygen.”

In order to reduce the risk of choking, parents and caregivers can do their part by following these safety tips:

• Do not give children younger than 4 any round, firm foods unless they have been cut into very small pieces. Cut hot dogs lengthwise and cut grapes into quarters. This changes the dangerous round shape that can block a young child’s throat.
• Do not give toddlers other high risk foods, such as hard candy, nuts, seeds and raw carrots.
• Never let small children run, play or lie down while eating.
• Keep coins and other small items out of reach of young children at all times.
• Carefully read warning labels on toys before giving them to young children.
• To check if a part of a toy is too small, use a small parts test device, which is available at many toy stores.
• Additionally, parents and caregivers should learn first aid for choking and cardiopulmonary resuscitation (CPR) in the event a choking episode occurs.

Internal and Environmental Factors Trigger Unique Brain Activity in Teens

 

While the otherworldly behavior of teenagers is well documented, University of Pittsburgh researchers have taken a significant step toward finally unraveling the actual brain activity that can drive adolescents to engage in impulsive, self-indulgent, or self-destructive behavior. Published in the current edition of Behavioral Neuroscience, the Pitt study demonstrates that adolescent brains are more sensitive to internal and environmental factors than adult brains and suggests that the teenage tendency to experiment with drugs and develop psychological disorders could stem from this susceptibility.

Lead researcher Bita Moghaddam, a professor in the Department of Neuroscience in Pitt's School of Arts and Sciences, said that although the exact mechanics of the adolescent brain's reaction need further investigation, the current study is a starting point in mapping the neural path from stimuli to behavior in the adolescent brain. Pitt neuroscience doctoral student David Sturman was the Behavioral Neuroscience report's lead author, conducting the study with Moghaddam and Pitt research assistant Daniel Mandell. The project was supported by the National Institute of Mental Health.

"Adolescence is a period of volatility and vulnerability with tendencies toward interpersonal conflict, emotional reactivity, and risk behavior, but we know very little about the brain mechanisms that promote this state," Moghaddam said. "We want to know how the adolescent brain interacts with the environment at the brain-cell level, when the neural signals are firing. Once we identify how certain factors trigger teenage behavior, we might better understand-and possibly address-the origin of the risk taking and psychological disorders such as depression and schizophrenia that occur during this period."

The researchers trained adolescent and adult rats to respond to a visual light cue by rewarding them with sugar pellets. Previous research has shown that adolescent rats and mice exhibit behavioral differences from adults similar to those of adolescent humans, including greater impulsiveness, impatience, and vulnerability to psychological problems, the authors wrote. The rats were placed in front of three holes with the light behind the middle hole. If a rat poked its nose into the center hole when the light was activated, it received a pellet; if it explored the right or left hole, it got nothing. The researchers found that the adolescents responded to the light cue at least as readily as adult rats, suggesting a similar or slightly better capacity for learning.

After six days, the rats no longer received a reward for choosing the center hole. They were divided into four test groups, each with an equal number of adults and adolescents: rats that were given 20 percent less food between sessions and received the light cue; rats that received the light cue but could eat as much as they liked between sessions; a group that received less food and no light cue; and a group that could eat between sessions but was not shown the light cue during the experiments.

Moghaddam and her team found that adolescents tended to return to the center hole far more often than the adults although they received no reward and continued going to the hole long after the adult rats stopped altogether. Such doggedness was even more prominent in adolescents who received the light cue and had a restricted diet before the experiment. This group nosed the center hole 30 times, twice as often as adults under the same circumstances and as adolescents with less food and no light cue. Adolescents that received the cue and had free access to food made for the center hole only a third as often.

Thus, rats experiencing internal and external stimuli-hunger and the light cue-compulsively sought the earlier reward long after the other rats realized it no longer existed. These results suggest that human teenagers can similarly behave irrationally and compulsively when faced with certain feelings and settings, Moghaddam said. "A scenario could range from the relatively mundane, such as hungry teenagers being more likely than adults to buy fast food immediately after seeing an advertisement, to despair and relationship problems eliciting thoughts of suicide," she said.

For the project's next phase, the Pitt group will repeat the experiments while monitoring activity in the emotion and cognition centers of the adolescent and adult rats' brains, Moghaddam said. This information will help Moghaddam and her colleagues grasp how brain cells encode the behavioral signals sent in response to stimuli.