L.R.. <br/><br/>
Too many comets :   Astronomer doubts the numbers, not the effects, of cosmic collisions. 

 - Oregon-XXU :   The Leach Publishing Group,   1999. 
 - p. 73 :   il. 
 - Bimestral 
 - Vol. I, no. 4, (Jul./Aug. 1999) 
 - Discovering Archaeology ;   no. 4 .
 - Estados Unidos.   The Leach Publishing Group. .
<br/><br/><br/>Art¡culo en inglés.