On the horizon: news from the frontiers of science

Ancient Mayans liked tapioca, too; astronomers are startled by the absence of dark matter; ape ancestors are much older than we thought.

Proof that Mayans enjoyed tapioca

The hunt for the missing tapioca is over. Archaeologists announced this week that they have discovered a 1,400-year-old field of manioc – aka tapioca – at the ancient Mayan farming town of Ceren in El Salvador. The discovery represents the best evidence to date that Mayans grew more than corn and beans to sustain their civilization. Indeed, it's the first conclusive evidence anywhere in the New World for manioc cultivation, the researchers say.

Manioc is a woody plant with starchy roots. Some researchers estimate that it was first domesticated in Brazil 4,000 to 5,000 years ago. Scientists had seen bits of burned manioc at Mayan sites, but they were not able to date it or tell if the tubers were farmed or wild.

At Ceren, a team of US and Salvadoran scientists led by the University of Colorado's Peyton Sheets discovered several large parallel planting beds beneath 10 feet of volcanic ash, deposited during a nearby eruption about AD 600. After carefully excavating part of the garden, the team used dental plaster to fill in hollows that the long-decomposed tubers had left in the hardened ash. The effort yielded plaster replicas of manioc roots. In addition, they found evidence that some of the stalks had been planted shortly before the eruption.

"Manioc's extraordinary productivity may help explain how the Classic Maya at huge sites like Tikal in Guatemala and Copan in Honduras supported such dense populations," Dr. Sheets explains.

A startling absence of dark matter

It's an axiom of astronomy that dark matter and galaxy clusters go hand in hand: No matter how violently these clusters collide, the dark matter sticks with the galaxies.

Until now. Astronomers at the University of Victoria in British Columbia say they've spotted a cluster collision that has a dark-matter core and a puzzling lack of galaxies. Astronomers can't see dark matter: They infer its presence by its effect on the matter they can see – in this case, the galaxies and the vast expanses of hot gas galaxy clusters contain. The cluster in question is Abell 520. And beyond its nearly empty dark-matter core, the scientists say they found a small group of galaxies that yielded no evidence of dark matter nearby. How did this "inseparable" pairing – galaxy clusters and dark matter – come unstuck? And does the explanation merit a footnote or a substantial revision of astrophysics textbooks?

The team speculates that the two types of matter – dark and light – became separated through a complex series of gravitational interactions that tore the two apart. Or maybe dark matter is affected by its own unique set of interactions in addition to gravity. But that would require new ideas in physics to explain it. The results are slated to appear in October in The Astrophysical Journal.

Apes are older than we thought

Gorillas have new great great great great great (etc.) grandparents. A team of scientists in Ethiopia have uncovered what they interpret as fossil evidence for a new species of great ape. The first of the fossils – all teeth – was found in February 2006. Then, last March, researchers found eight more. All were found at a site about 100 miles east of Addis Ababa.

The team says the fossils represent a creature directly related to today's gorillas, chimpanzees, and bonobos. The researchers add that the find also suggests that ancient ancestors of humans and African great apes began to walk their separate evolutionary paths far earlier than genetic studies indicate. Molecular evidence suggests that the lines leading to humans and to gorillas diverged about 8 million years ago; the age of new fossils suggest it occurred at least 2 million years earlier, the team says. The results appear in today's issue of the journal Nature.