Preface	GHOSTLY APPARITIONS IN THE NIGHT    11
One	FROM DUST TO DUST    17
Two	FOUR BILLION YEARS AGO    37
Three	COMETS AND THE ORIGIN OF LIFE    57
Four	THREE BILLION YEARS AGO    71
Five	SIXTY-FIVE MILLION YEARS AGO    87
Six	COMETS ARE DOUBLE-EDGED SWORDS    103
Seven	EARTH'S FIRST COLD WAR    115
Eight	A TIME FOR COMETS    125
Nine	A FIELD OF DREAMS    139
Ten	TARGET EARTH    153
Eleven	THREE LITTLE WORLDS    173
Twelve	PROBING FOR LIFE IN OUR GALAXY    185
Thirteen	YES, VIRGINIA, COMETS DO HIT PLANETS    197
Fourteen	PRESCRIPTION FOR DOOMSDAY    215
Fifteen	AN EPILOGUE    231
	NOTES    239
	INDEX    245