On the horizon: news from the frontiers of science

Man's first seafood meal 200,000 years ago, Titan's liquid-methane clouds, and an invasive reed's poisonous tactics.

Humanity's first seafood epicures

Surf and turf is a popular choice at many local bistros. It apparently was also a hot combo 164,000 years ago.

Scientists sifting through remains in a South African coastal cave say they have uncovered some of the earliest evidence yet for seafood consumption by Middle Stone Age Homo sapiens. For millions of years, ancestors of the first anatomically modern humans lived off of plants and land animals. For Homo sapiens, who started to emerge in Africa some 200,000 years ago, seafood represented one of the last major food sources humans learned to exploit before they figured out how to domesticate plants and animals. Previous studies had indicated that early humans began developing a taste for seafood some 125,000 years ago.

The remains indicate that the cave's inhabitants ate whelks, barnacles, mussels, and limpets. The international team of researchers, led by Curt Marean and Peter Nilssen of Arizona State University, notes that shellfish may have been crucial to early human survival. At the time, the ice-age climate had dried out southern Africa. This development would have reduced the land-based food supply for bands of early humans, forcing them to exploit easy-to-reach food resources in tide pools. The results appear in today's issue of the journal Nature.

Strange rain on Titan

Astronomers tracking weather on Saturn's moon Titan say they have spotted a vast, high-altitude patch of clouds that drizzle liquid methane onto the moon's surface. The cloud, which lies beneath higher-altitude clouds of frozen methane, appears in the predawn period over the western foothills of a continent scientists have named Xanadu.

Because of Titan's frigid temperatures, any water would be frozen solid. But hydrocarbons such as methane liquefy and go through similar processes of evaporation, condensation, and precipitation.

Astronomers trained the 10-meter Keck telescope in Hawaii and the European Southern Observatory's Very Large Telescope in Chile on the moon and used infrared imaging to tease out the liquid-methane cloud, which appears at an altitude of about 19 miles above Titan's surface. Modeling results indicate that the drizzle droplets are about one millimeter across.

Because the cloud appears as dawn breaks – Titan's "day" is 16 Earth days long – and dissipates after the moon's lengthy "midmorning," the drizzle events could be analogous to conditions on Earth in which on-shore winds drive moist air toward coastal mountains. There, the air rises and moisture falls out as rain, notes Imke de Pater, a University of California at Berkeley astronomer and a member of the team reporting the discovery. The results appear in the current issue of Science Express, the online companion to the journal Science.

Pesky reed has a deadly weapon

US wetlands have come under increasing pressure from an invasive reed, and scientists have traced its success to a vile criminal act – it poisons surrounding plants.

The perpetrator in this case is an imported form of Phragmites australis, a reed found throughout the world. While a less-aggressive strain existed in the US before the more aggressive form was imported, the import has been expanding its turf at the expense of a range of native wetlands plants, researchers say. Until now, however, the key to its success was unknown.

A team led by biologist Harsh Bais found that P. australis's roots emit a toxin acidic enough to destroy cells in the roots of neighboring plants. Many plants are known to release toxins that discourage other species from growing nearby – a bit like setting up biochemical No Trespassing signs. But P. australis's toxins actively destroy its neighbors.

Armed with this information, researchers say they hope to develop strategies to counter the invasion. The results appear in the current issue of the Journal of Chemical Ecology.

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