------------------------ Soup or Sandwich IN THE VERY BEGINNING, about 4.6 billion years ago (give or take a few years), a small ball of rock, water and gas had come to be and immedi- ately set about the process of combining its atoms into more and more complex arrangements. Thus began that most wondrous story, the evolu- tion of life on Earth. For the first 2.1 billion years of the Earth's existence, the Archeo- zoic Era, life very slowly evolved. The Earth's crust was still in flux and covered for the most part by shallow seas. ....