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ENVIRONMENT Silver lining in air pollution LEIPZIG, GERMANY - High levels of pollution have been found 30,000 feet above the earth's surface, according to Jost Heintzenberg, director of the troposphere research institute here.

He said aerosol particles at this altitude originated mainly from dirt on the earth's surface and not from aircraft.

Aerosol particles are small, insoluble liquid or solid particles suspended in a gas. Scientists say the particles have as much influence upon climate changes as greenhouse gases. Mr. Heintzenberg said the level of particles increased at high altitudes when clouds built up.

But pollution might not be all that bad, say other researchers. Scientists from Italy and the US found that organic compounds from some pollutants can increase the number of water droplets in clouds. With more droplets, the clouds are brighter and reflect more sunlight. This results in less light reaching the earth below, making it cooler. This may deter some of the effects of global warming. Clouds in Italy's Po Valley were found to have organic compounds in the water, from sources like the burning of agricultural waste. If 1 percent more sunlight is reflected away from the earth, a change to local temperatures could take place.

SCIENCE Alas, Lucy meets Yorick RIO DE JANEIRO, BRAZIL - Anthropologists here unveiled the oldest known human fossil in the Americas, a woman's skull with African features that could revolutionize theories on the continent's early inhabitants. Scientists dubbed the woman - who lived 11,500 years ago - "Luiza." Before Luiza's appearance, paleontologists had been working on the theory that the earliest Americans were Asian ancestors of the Native Americans that European colonizers encountered when they arrived on the American continent 500 years ago.

The fossil - found in Brazil in 1975 - shows there were humans on the continent long before Asians came.

- Compiled from news wires by Lane Hartill

(c) Copyright 1999. The Christian Science Publishing Society