How might the incompleteness of the fossil record play a role in such theories as the Cambrian explosion of life? Of what are comets made? And asteroids? What is Earth's mantle? What elements make up the Earth's mantle? How are comets different from...
in the asteroid belt (the velocity of apparent motion of neighbor asteroids can ach ieve several k ilometers p er second). 2.2 C omets C o mets are lo ng—distance trav elers .A phelions of th eir o rbits lie far beyond t he giant p lanet s.W hen ap pro aching the...