"Earth Science" is a combination of various scientific disciplines that deal with the planet earth in the most general macroscopic level. Different branches of earth science encompass geology, oceanography, climatology, meteorology, and even for the purposes of understanding the position of the Earth in the Universe, astronomy.
This is by and large a very approachable and well presented introductory earth science textbook, and it is written with a high school student or beginning college student in mind. Topics covered include earthquakes, volcanoes, plate tectonics and the continental drift, mineralogy, erosion, oceans, atmosphere, climate, the impact of humans on earth, and many others. The book concludes with a few chapters that take us beyond Earth, and aim to describe Earth's place in the Universe as a whole.
Each chapter ends with a several questions, most of which are not quantitative. In fact, this is not a very quantitatively oriented textbook, and it stresses critical and scientific thinking over quantitative skills. However, it is a very interesting and well organized textbook and provides an excellent introduction to earth science. In addition to questions, there are also numerous vocabulary terms listed at the end of each chapter. These provide the student with an opportunity to systematize the knowledge gained in the preceding chapter.
There are many illustrations and photographs throughout the textbook, and they are generally of high quality and on the average much better than in most other CK-12 textbooks.
This book is available under the Creative Commons License through the CK-12 foundation, which means it can be reprinted, modified and resold if necessary. It is also a fairly large file, pdf version being about 1500 pages long, so be prepared for a longish download.
The Kindle formatting of this textbook leaves something to be desired. The book was originally typeset in LaTeX, and this did not translate all that smoothly into the Kindle format. I've found that getting this textbook on other e-readers or computers in the epub format rendered it much more satisfactorily.
This is probably one of the best presented and formatted of all CK-12 textbooks, and comes closest to being a completely viable alternative to a traditional textbook.