In
trying to understand the formation of the early Earth, some researchers have suggested that the planet was dry and inhospitable to life until
icy comets pelted Earth and deposited
water on the surface.
Jim Green: The Snowball Earth era reminds me of several objects in the Solar System now that we're
trying to study, one of which is Europa, [which has] got this fabulous
icy crust over the whole moon and underneath it perhaps as much as twice the volume of
water than exists here on Earth.