But comets may have helped create life, too. Earth was hot and possibly sterile for its first half billion years, yet the fossil record shows that life began soon after that about 3.8 billion years ago. Comets were more plentiful back then and they collided with our planet frequently. Well, among other things, comets contain hydrogen, oxygen, and water. These celestial icebergs may have delivered the raw materials needed to build up Earth's oceans and atmosphere.
Speculation abounds as to just how much organic material fell to Earth long ago.
More observations are needed to solve this intriguing mystery. New clues should arrive soon. The probe will veer to within 150 km of Comet Wild in 2004 and collect dust shed by the comet's head. Then it will return the material to Earth for study. Feeling right at home in the Milky Way.