1.   A steady fall of cometary ice, some scientists say, also helped to inundate the world and perhaps sowed organic molecules associated with life.

2.   It is in the shadow of these deep walls that the cometary ice has apparently accumulated as a mixture of dirt and rock.

3.   It suggests that cometary ices are identical to those of deep interstellar space and that both bear in their crystals the precursors of life.

4.   Moreover, astronomers increasingly see cometary ices as bearing the chemical precursors of life.

5.   Instruments on telescopes are able to determine the composition of cometary ice by analyzing the clouds formed when the ice turns to gas, he said.