Tracking seal dives off Antarctica reveals seafloor troughs that affect ocean circulation. (p. 12)

The verdict is in on this year’s Arctic sea-ice melt: third worst since satellites began keeping track of the northern polar cap in 1979. Satellites and scientists continually monitor the Arctic Ocean’s skin of ice, which melts back in the summer and expands again in the winter. Researchers have been watching the ice’s decline with increasing alarm, especially after the summer of 2007 brought a record-breaking minimum. Ice extent recovered a bit in the summers of 2008 and 2009, but the long-term trend is unmistakable: The ice is shrinking in extent as well as thinning. Thinner ice is mo... (p. 10)

The verdict is in on this year’s Arctic sea-ice melt: third worst since satellites began keeping track of the northern polar cap in 1979. Satellites and scientists continually monitor the Arctic Ocean’s skin of ice, which melts back in the summer and expands again in the winter. Researchers have been watching the ice’s decline with increasing alarm, especially after the summer of 2007 brought a record-breaking minimum. Ice extent recovered a bit in the summers of 2008 and 2009, but the long-term trend is unmistakable: The ice is shrinking in extent as well as thinning. Thinner ice is mo...

View the slide show SVEIFLUHÁLS, Iceland — High atop an Icelandic mountain one magnificent summer day, with blankets of soft moss underfoot and a translucent lake shimmering in the valley below, geologist Emily Constantine Mercurio is conjuring up an image of hell. Tens of thousands of years ago, says Mercurio, a graduate student at the University of Pittsburgh, this place was the heart of a roiling volcanic eruption. Molten rock bubbled up from a fissure in the Earth’s crust. On top of that lay hundreds of meters of ice. Lava met ice, and the result was an inferno. Heat from t... (p. 16)

Rocks in Nevada preserve evidence of superfast changes in Earth’s magnetic polarity. (p. 10)

A classic Canadian fossil trove extends to thinner deposits, geologists find. (p. 10)

Solids are supposed to be the reliable state of matter. Gases are flighty and flitting and expand to fill any available space. Liquids will also mold themselves to whatever shape they occupy, from soda bottle to swimming pool. Solids, though, are steadfast and unyielding, stable and dependable, like the rise and fall of tides, the guidance of the North Star or the love of a dog. But that truism may turn out not to be so true. In the past few years, physicists have learned of a solid that doesn’t adhere to fixed rules. Within this solid — helium at very low temperatures — some a... (p. 22)

Ancient DNA experts say they are analyzing a lock of Sitting Bull's hair.

The moon’s interior contains far less water than Earth’s, new studies of rocks collected by Apollo astronauts suggest. (p. 12)