On the horizon

News from the frontiers of science.

Better mercury scrubbers

It's tough trying to scrub mercury pollution from the mud at the bottom of streams, rivers, and lakes. Now, scientists say they have devised an approach - for the time being, in the beaker - that may provide an efficient solution.

They used ultrasound to shake mercury loose from contaminated mud. Then they used genetically altered microbes to break down the mercury once it entered the water. Other techniques can absorb mercury, says the team from Ohio State University, but a wide range of metals is also absorbed at the same time. By using microbes genetically tuned for specific metals, the ultrasound-microbe approach could remove toxins more efficiently, researchers say.

In the lab, the microbes munched as much as 60 percent of the mercury freed from the soils within a few seconds of its release. The system removed 30 percent of the mercury from the soil a few minutes after it was activated.

The team described its experiments this week at the annual meeting of the American Chemical Society in Atlanta.

A new class of comets

Astronomers say they have discovered a new class of comets that ramble among asteroids that orbit the sun between Mars and Jupiter. The discovery, the astronomers say, supports the notion that some of Earth's water came from ice-rich objects in the main asteroid belt.

Typically, comets come from two regions of the solar system: the Kuiper Belt, which lies between 30 and 50 astronomical units (AU) from the sun; and the Oort Cloud, which ranges from 3,000 to 50,000 AU. One astronomical unit is equal to the distance between the Earth and the sun - roughly 93 million miles.

Two astronomers from the University of Hawaii have studied three objects in the asteroid belt that have tails, a feature comets display when they approach the sun and warm up. Typically, the ices in comets vaporize as the objects approach the sun and warm, generating luminous tails of gas and dust. In this case, the astronomers suspect that collisions with other asteroids exposed the icy contents of these new objects, whose orbits closely match those of their asteroid cousins.

So far, the scientists have three "main-belt comet" candidates. They estimate that the asteroid belt could host 15 to 150 more of these comets that are currently active. The results appear in Sciencexpress, an online publication of the journal Science.

Another 'missing link'

Scientists working in Ethiopia say they have unearthed the fossilized remains of a human ancestor they estimate to have lived between 500,000 and 200,000 years ago. The researchers say the specimen could help fill a gap in the fossil record tracking the evolution of modern humans from Homo erectus.

Scientists came across the remains last month as they surveyed a gully that feeds the Gawis River. The team found significant portions of the human's skull, including its upper face, upper jaw, and cranium. The features are clearly more primitive than those of today's humans, the researchers say. But, they add, the features also clearly identify the creature as an ancestor to modern humans. Nearby, in the same layer of silt and sand, scientists also have found stone tools and fossilized remains of pigs, zebras, elephants, and other animals.

The research team, from the Stone Age Institute in Bloomington, Ind., and Indiana University, says that more precise dates will have to come from analyzing layers of volcanic ash above and below the layer in which they found the skull pieces.

Once those measurements are made, however, the team says it expects the fossil to be one of the best-dated human ancestors found yet.

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