Scientists have known for some time that most major groups of complex animals appeared in the fossils record during the Cambrian Explosion, a seemingly rapid evolutionary event that occurred 542 million years ago. Now paleontologists, using rigorous analytical methods, have identified another explosive evolutionary event that occurred about 33 million years earlier among macroscopic life forms unrelated to the Cambrian animals.

  Asteroid impacts or massive volcanic flows might have occurred around the time dinosaurs became extinct, but a new argument is that the mightiest creatures the world has ever known may have been brought down by a tiny, much less dramatic force -- biting, disease-carrying insects.

  Heart attack patients in the U.S. are far more likely to receive a blood transfusion than patients in other countries with the very same condition, but the outcome of their treatment is no better. Increasing evidence suggests transfusions may not only be unnecessary but may actually be harmful to some patients.

  Right now, one in four hospitalized Americans has a urinary catheter. But despite the fact that catheter-related urinary tract infections are the most common hospital-acquired infection, and can lead to dangerous complications, a new study shows hospitals aren't using proven tactics to prevent such problems.

  Children with cancer have a higher prevalence of body abnormalities, such as asymmetric lower limbs and curvature of the spine, suggesting that the genetic defect responsible for the abnormality may play a role in the development of cancer, according to a new study.

  Hydrogen peroxide, the same mild acid that many people use to disinfectant their kitchens or treat cuts and abrasions, is also produced by the body to keep cells healthy. Now, researchers have solved how part of this complex process works.

  Phantom noises, that mimic ringing in the ears associated with tinnitus, can be experienced by people with normal hearing in quiet situations, according to new research. Tinnitus, an auditory perception that cannot be attributed to an external source, affects at least36 million Americans on some level, with at least seven million experiencing it so severely that it interferes with daily activities.

  Researchers, using machine learning and brain imaging, have found a way to identify where people's thoughts and perceptions of familiar objects originate in the brain by identifying the patterns of brain activity associated with the objects. Scientists were also able to accurately determine which of the 10 drawings a participant was viewing based on their characteristic whole-brain neural activation patterns.

  In the first study examining American physicians'use of placebos in clinical practice in the 21st century, 45 percent of Chicago internists report they have used a placebo at some time during their clinical practice.

  Soccer teams from high altitude countries have a significant advantage when playing at both low and high altitudes, finds a new study. In contrast, lowland teams are unable to acclimatise to high altitude, reducing physiological performance.

  Two large-scale studies report that the chances of surviving cardiac arrest are no better -- and may be worse -- when bystanders perform mouth-to-mouth breathing than if they press on the chest without interruption. The results are in line with experimental findings showing that neurologically normal survival was better with continuous chest compressions than when following the standard CPR protocol of 30 compressions and 2 ventilations.

  Hospitalized patients who suffer a cardiac arrest are more likely to survive if their hearts are shocked back into rhythm within two minutes, but 30 percent of such patients aren't getting help fast enough.

  Obese people are less likely to use their seatbelts than the rest of the population, adding to the public health risks associated with this rapidly growing problem. Seatbelt use declined as BMI increased, with approximately 55 percent of extremely obese individuals reporting they did not use a seatbelt.

  Fifty years after the Nobel-prize winning explanation of how superconductors work, scientists are suggesting another mechanism for the still-mysterious phenomenon and exploring new superconductor candidates. Among the classes of materials that appear capable of superconductivity without phonons are the so-called heavy electron superconductors, certain organic materials, and the copper oxide materials that superconduct at up to twice the temperature at which nitrogen liquefies.