Montgomery: Environmental Geology Answers to End of Chapter Review Questions CHAPTER 1 1. Describe the process by which the solar system formed and explain why it led to planets of different compositions, even though the planets formed simultaneously. The solar system formed by collapse and condensation of a rotating cloud, or nebula, of dust and gas. Most of the mass coalesced to form the Sun, and most of the remaining condensed into protoplanets and then planets. Because the planets formed in the presence of a temperature gradient created by the young Sun, different planets have different compositions: those forming closest to the Sun consisting predominantly of minerals with high melting temperatures and very little water and gas; those farther away, of minerals with lower melting temperatures; and farthest away, of condensed gases. 2. Compare the age of Earth with the length of time humans have both inhabited the planet and come to influence their geologic environment. Earth is 4.5 billion years old. The earliest remains from the Homo genus are 1.5 to 2.5 million years old. Only within the last few centuries has the human population grown to the point that human impacts are significant on a global scale. 3. Explain how the newly formed Earth differed from the Earth we know today. The newly formed Earth was solid and likely not differentiated internally as it is now. The internal layers developed with time as Earth cooled and materials segregated by density. Early Earth also lacked oceans and an atmosphere. 4. List the kinds of information that are used to determine Earth's internal composition. Scientists determine Earth’s internal composition by studying a variety of indirect evidence which includes Earth’s density and mass, the composition of both meteorites and of the solar nebula from which Earth formed, and geophysical evidence of Earth’s internal layering. 5. Outline the processes by which Earth’s atmosphe