On the horizon

Advanced culture in Uruguay

The discovery of a 4,000-year-old farming village in Uruguay is challenging current theories of how complex cultures developed in South America.

The Los Ajos site, located on the Atlantic coast near Uruguay's border with Brazil, includes 15 mound complexes. They contain evidence that residents farmed maize, squash, and beans. In addition, over the years, Los Ajos was altered in ways that suggest that the region was more densely populated at the time than previously believed.

The find is startling because the region traditionally has been written off as archaeologically marginal, say the archaeologists from the United States and Uruguay who uncovered the site. The work, other researchers say, adds to a growing body of evidence that is confounding long-held notions that complex cultures in South America emerged from a central region on the Pacific coast and in nearby Andean highland valleys, then spread to the rest of the continent.

Beyond its assault on conventional wisdom, Los Ajos also suggests that evidence for complex prehistoric cultures also may emerge from other parts of the continent thought "marginal," notes University of Binghamton anthropologist Peter Stahl.

The team from the Smithsonian Tropical Research Institute, the Florida Institute of Technology, and three Uruguayan institutes reported their results in Thursday's edition of the journal Nature.

They came by the billions to the eastern US in May and June - small, cacophonous, winged bugs called "periodic" cicadas. Every 17 years they emerge from underground in landscape- shrouding droves, reproduce, then die.

For humans, the cicada party is annoying. But new research suggests North American forests love it.

Other researchers already had observed a curious increase in forest wood growth in years following cicada infestations. So, in field tests during three successive years when the bugs emerged in different parts of the East, Louie Yang, with the Center for Population Biology at the University of California at Davis, looked at the effects of deceased cicadas.

Perhaps not surprisingly, he found that the cicadas enriched the soil. They added nitrogen, stimulated the growth of plant-friendly soil microbes, and ultimately triggered a growth spurt among key forest plants.

The results, he writes in the current issue of the journal Science, point to a profound effect a single insect genus can have on entire ecosystems, particularly in "pulses" - sudden, unusual increases in nutrients or other basics that organisms in an ecosystem need.

Cicadas, it turns out, could affect changes in forest ecosystems across wide swaths of territory, and with lasting effect.

For several years, climate scientists have puzzled over a set of contradictory evidence on global warming. Global average temperatures at ground level have been rising, but satellite readings of temperatures in the lower atmosphere as a whole have not shown the same trend. If the climate is warming, both sets of temperatures should show it.

Now, a team from the University of Washington led by atmospheric scientist Qiang Fu appears to have solved the conundrum - concluding that temperatures in the lower atmosphere, or troposphere, have in fact been rising.

The work, set for publication later this month in the Journal of Climate, indicates that the satellites have been fooled by cooling trends in the layer just above the troposphere. The idea isn't new; the same team published work earlier this year that reached the same conclusion. But critics took aim at the team's method, which in essence subtracted satellite measurements of stratospheric temperatures from those taken in the troposphere. The critics argued that that technique overcompensated for stratospheric cooling.

This time, the team used direct measurements of stratospheric temperatures to correct the satellite measurements. The results closely match its previous findings. Combined with the team's earlier work, this new, independent approach constitutes "quite powerful evidence" that the troposphere is warming, along with surface temperatures, Dr. Fu notes.