New Planetary Geology Chapter
On the advice of our reviewers, we have added a chapter on planetary geology (chapter 22), whose material is entirely new to the book. This chapter was written by Tom Arny, Emeritus of the University of Massachusetts, author of the successful McGraw-Hill Explorations astronomy textbooks.

Exceptional Illustrations
Every illustration and photo has been evaluated for accuracy, currency, and visual appeal, and has either been replaced, updated, or otherwise revised where necessary. This sixth edition features more than 80 new illustrations and 45 new photos. In addition, over 200 illustrations have been revised and redrawn. The new illustrations were created in consultation with Dr. Abhijit Basu of Indiana University, and thoroughly reviewed by a panel of nine advisors to contribute to a visually spectacular and pedagogically sound art program.

Content Changes
Some of the significant content changes include:

• An integration of the Earth systems approach to geology is introduced in Chapter 1 and subsequent chapters include a section relating chapter material to Earth systems. The hydrologic cycle in chapter 16 has been rewritten to reflect Earth systems.
  

• Earth systems are discussed in new boxed readings. For example, in chapter 3, we discuss the effect of tides on shallow earthquakes along the Juan de Fuca Ridge. In chapter 9, we explain what we've learned about past climate changes from studying oxygen isotopes.

• Astrogeology boxes have been retitled as Planetary Geology. There are fewer boxes throughout as many topics are now covered in the new planetary geology chapter. We have retained those boxes that are particularly appropriate to the topic at hand. We have also added a box on wind features on Mars.

• The importance and use of stable isotopes in geology is described in chapter 9 and includes a new Earth systems box on oxygen isotopes and global climate change.

• A section has been added to the chapter on volcanism (chapter 10) on the influence of volcanoes on religious or supernatural beliefs in cultures that live with volcanoes.

• In the chapter on geologic time we introduce the new technique of cosmogenic exposure dating which uses isotopes to determine how long a surface has been exposed to bombardment from solar radiation.

• A section on underwater landslides has been added to the mass wasting chapter.

• In the earthquake chapter we have a discussion and photo of the November, 2002 Denali earthquake in Alaska. We have added new information on how an earthquake triggered submarine landslide may have increased the size of the 1998 Papua, New Guinea tsunami. The earthquake prediction section was substantially rewritten.

• Some of the descriptions of the geologic occurrence of geologic resources have been moved from chapter 21 (geologic resources) to appropriate chapters. For instance, the portion on ore deposits associated with hydrothermal activity has been moved to chapter 15. This is in response to many instructors who don't have time to cover chapter 21, but nevertheless want important resources to be part of their courses.