The ratio of carbon dioxide reached 400 parts per million Sunday in readings taken by the two top monitors of greenhouse gases.

The National Oceanic and Atmospheric Administration revised its Sunday reading to 400.06, following a Sunday reading of 400.15 by the Scripps Institution of Oceanography.

Both measures came from the top of Mauna Loa volcano in Hawaii, and are considered an important bellwether for the status of Earth's atmosphere. Readings have exceeded that milestone in the Arctic but had not reached the level in the temperate latitudes in the middle of the Pacific Ocean, far from...

A schoolmate's suicide is associated with thinking about or trying suicide among teenagers, researchers report.

There has long been a theory that suicide is "contagious," meaning exposure to it can increase the risk, but there have been few studies that delve into the possibility. In a study published Monday in the Canadian Medical Assn. Journal, researchers surveyed thousands of teenagers about the effects of suicide by someone they knew or attended school with.

"Adolescents may be particularly susceptible to this contagion effect," wrote researchers from the Harvard School of Public Health...

All psychotherapists -- and most criminal attorneys -- know that memories are fragile things. Once a seemingly well-entrenched memory for a given event -- what psychologists call a declarative memory -- is taken out for inspection, it is subject to being frayed, recolored, reinterpreted and altered. The result is that when that when a memory is returned to long-term storage, it can bear little resemblance to the memory that was laid down initially, or which has been brought out before and subject to change.

A new studyfinds there is one more thing a bystander can do when someone pulls out a...

A coalition of environmental groups has filed a lawsuit in federal court accusing transportation agencies of violating migratory bird laws by installing protective netting across two bridges in the Petaluma, Calif., area that has injured and killed dozens of migrating cliff swallows.

A Caltrans contractor draped the nylon netting over the Petaluma River and Lakeville Overpass bridges along Highway 101, about 30 miles north of San Francisco, as part of an effort to deter cliff swallows from nesting under them, according to the lawsuit.

Each spring, cliff swallows migrate 6,000 miles from...

The aggressive red fire ant Solenopsis invicta has become a scourge of the southern United States, spreading like wildfire and delivering burning stings to unfortunate victims. Now, researchers spying on the ants' underground chambers have learned that their tunnel-building follows a simple, perhaps universal, rule.

The discovery, published Monday by Proceedings of the National Academy of Sciences, could provide insight for engineers building search-and-rescue robots.

Native to the Pantana wetlands of South America, the ants somehow hitched a ride to Mobile, Alabama about 80 years ago. From...

Having childhood attention deficit hyperactivity disorder could lead to a life of obesity, even if ADHD symptoms disappear in adulthood, a new study shows.

The study, which followed up on 207 middle-class men who had been diagnosed with ADHD as children, found that some 33 years after their diagnosis, their body mass index was significantly higher than those without ADHD. Their propensity to become obese was twice that of adults who were never diagnosed with ADHD, according to the study published Monday in the journal Pediatrics.

Even those who did not have the disorder as an adult were...

How did we go from a lifeless Earth with no oxygen to a planet teeming with life and that essential element? Scientists at the Georgia Institute of Technology have found one crucial clue: iron and RNA.

The team managed to re-create conditions of life on Earth 3 billion years ago and"revived" a function of RNA that may have subsided after the rise of DNA.

Life as we know it depends on the precise interplay of DNA, the double-helix molecular structure that safeguards genetic code, with RNA and proteins. But many scientists -- among them Francis Crick, who, with James Watson, discovered DNA --...

Finally. After many contentious years, the American Psychiatric Assn. has unleashed DSM-5, the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders.

If you know one thing about the DSM, it’s probably that this book is considered “the bible of psychiatry.” According to the APA, it “contains a listing of diagnostic criteria for every psychiatric disorder recognized by the U.S. health care system.” Psychiatrists rely on it, as do other doctors, psychologists, nurses, social workers, folks at insurance companies who figure out which conditions...

The sun has a distant twin, but it’s 2 billion years older. And if the star at the center of our solar system evolves like its relative out in the Unicorn constellation, all the water on Earth will boil away.

The newly discovered star is the farthest of the so-called solar twins in the Milky Way galaxy. Twins get their name because they have nearly identical mass and chemical composition, not because of any shared birthday. In fact, the differences in age are one reason solar twins are so important to astronomers – one star may be a snapshot of the other’s future.

The...

The biggest explosion ever recorded on the moon was caused by a space rock roughly the size of a beach ball.

It weighed 80 pounds and was just over 1 foot wide, but it was going incredibly fast, traveling through space at speeds of 56,000 mph.

And when it collided with the moon, it exploded with the force of 5 tons of TNT, sending off a flash of light bright enough to see from here on Earth.

It was the largest explosion that scientists monitoring lunar impacts had ever witnessed, and it likely made a 65-foot wide hole in the already pock marked lunar surface.

PHOTOS: Stunning views of the Sun

After nine years on the job, NASA’s Mars rover Opportunity has finally broken a 40-year-old record for the longest distance driven on another world.

The Mars rover Opportunity has been exploring the Red Planet’s surface since landing in January 2004. The last record for any NASA vehicle was set by Apollo 17 astronauts in December 1972 when they drove a lunar rover 22.21 miles over the moon’s surface over three days. Opportunity finally inched past that mark Thursday, tacking on 263 more feet for a total distance traveled of 22.22 miles.

Why did it take the Mars rover nine...