A new genetic analysis indicates that only about 200 to 300 people crossed the ice age land bridge from Asia to become the founding population of North America. (p. 339)

Sudden venting of hydrogen sulfide from the deep sea could have caused the largest extinction in Earth's history by poisoning land animals and destroying atmospheric ozone that protects Earth from ultraviolet light. (p. 339)

New simulations suggest that the solar system's four biggest planets were once bunched together, setting up a planetary bowling game that rapidly and violently rearranged the structure of the outer solar system and tossed chunks of debris inward. (p. 340)

The sense of smell may have its own brain atlas. (p. 340)

Biomedical engineers aim to repair damaged nerves with a chemically modified conducting polymer that stimulates the growth of nerve cells. (p. 341)

People with depression have high concentrations of norepinephrine, a brain hormone, but electroshock treatment lowers these levels to the normal range. (p. 341)

Carbon nanotubes serve as the electron emitters that light up the screen of a new experimental, high-definition television display. (p. 342)

Scientists review the discoveries made by the Mars rovers after nearly 18 months on the Red Planet. (p. 344)

New antibiotics may be valuable weapons in the fight against tougher bacteria. (p. 347)

Making new fat from food intake, as opposed to using stored fat, regulates genes important for blood sugar, fatty acid, and cholesterol concentrations. (p. 349)

The Cassini spacecraft has spotted a new moon of Saturn, only the second known to lie within the planet's main rings. (p. 349)

An experimental drug combination that inhibits an enzyme that's abundant in tumor cells shows promise against several cancers. (p. 349)

X-ray scanners based on carbon nanotubes could make airport luggage screening and high-tech medical imaging more efficient. (p. 349)

A mystifying case of lead poisoning, which may have lasted more than a decade, turned out to have been caused by a swallowed shotgun pellet. (p. 350)

Nuclear batteries that will last for decades may have moved closer to reality with the demonstration of a silicon chip riddled with radioactive, tritium-filled pits where radiation is efficiently converted to electricity. (p. 350)

A new bike design for kids morphs from tricycle into bicycle as the rider gets moving, possibly easing the often-fearful starts at riding two-wheelers. (p. 350)

The pesticide spinosad, previously thought safe for bees, may damage their ability to forage for nectar. (p. 350)

(p. 351)