NEW YORK, NOV. 7 -- The chemical "seeds" for life on Earth may have arrived on dust that fell from disintegrating comets, a new analysis has suggested.

That would have occurred as Earth orbited through huge dust clouds rich in organic molecules, scientists said. The suggestion has been made before, but the new analysis found evidence for it in a recent discovery in Denmark. Kevin Zahnle and David Grinspoon of the National Aeronautics and Space Administration's Ames Research Center discussed the hypothesis in today's issue of the British journal Nature.

The Danish discovery, reported last year, was that some ancient soil contained concentrations of amino acids that apparently came from outer space. Amino acids are crucial to life. The amino acids appeared in strata above and below a layer rich in the element iridium, which some scientist say stemmed from the impact of a huge meteorite that led to the dinosaurs' extinction 65 million years ago. The scientists who found the amino acids suggested that they had arrived on the meteorite, an idea that met with some skepticism.

Zahnle and Grinspoon suggested that the meteorite was a chunk of a large comet that created a dust cloud lasting thousands of years. Dust from this cloud deposited the amino acids in the soil before and after the meteorite's impact, they proposed. Such a process could have provided raw materials for life if it also occurred far earlier in the planet's history, Grinspoon said in an interview.