Abstract
A
These issues present a challenge for those who wish to develop a course on astrobiology. Furthermore, the relative importance of the issues waxes and wanes when defining the audience. Hungry first- or second-year undergraduates who want a unique science course and who are inspired by the excitement of the Mars missions, Cassini, and New Horizons' stream of imagery of Pluto. What about graduate students who want to branch beyond their foundations in chemistry, biology, geology, and physics (as well as philosophy!)? In my experience working with both undergraduates in my home department as well as teaching summer courses for PhD students, I quickly realized that the breadth of astrobiology presents truly unique challenges when bringing everyone to a level plane to address bold new questions. At a minimum, it is clear that there needs to be multiple textbooks available to market to these distinctly different demographics.
Undergraduate textbooks in diverse science disciplines like astrobiology tend to be broad but thin. The assumption is that basic principles need to be covered and reintroduced, and the treatment is usually quick; that is, the subject is covered in a few pages with perhaps a pull-out box or examples interspersed in the text. Rich data tables tend to be limited, and subjects seems to end quickly in order to get to the next topic. Still, for a lecture-based classroom, particularly one that incorporates dynamic active learning, a textbook such as this may serve as a good foundation for classroom discussion and inquiry. Joseph Gale's Astrobiology of Earth (Oxford University Press, 2009) does an admirable job of serving as a first text on the subject. The overall coverage is highly slanted toward the more pure biology questions, with more limited treatment of geology (or geobiology) foundations than other textbooks. Critical contributions of chemistry and physics (such as EM radiation and oxygenation) are interspersed appropriately in the text.
The general flow of Gale's book follows a linear development from the origin of the Universe through early Earth conditions to the evolution of complex life. There is an entire chapter on the evolution of humans, though it mostly focuses on contemplating the possibility of what humans (Homo horribilis!) might do to the planet. While this section may not be common in astrobiology courses, Gale positions the textbook to lead to this chapter, and the content would lead to a very valuable discussion in an undergraduate course. The writing is clear, comfortable, and readable to an undergraduate population. My only real criticism is that the figures could be reevaluated, as some of the stock photos could be replaced with more meaningful models and larger illustrations.
In contrast to Gale's contribution, the recent Astrobiology: Understanding Life in the Universe by Charles Cockell (Wiley-Blackwell, 2015) provides a rich and robust treatment that is more suitable to upper-level undergraduates and graduate students. Cockell is no stranger to astrobiology books, most recently being a coeditor of the volume on Astrochemistry and Astrobiology (Smith et al., 2013). Cockell's contribution offers a distinctly different approach to bringing the complex, modern view of astrobiology to a general, but advanced, audience. After a brief but complete chapter defining astrobiology and providing a history of the field, the book spends the next six chapters focusing on life: how it originated, what are the known and modeled limits of life, and how Earth's biosphere serves as a model for extraterrestrial life. Like the rest of the over-400-page textbook, this initial sequence is quite thorough, providing details ranging from Gibbs free energy and chirality to the minutest details of eukaryotic cells. Unlike a typical introductory textbook that may serve as too rudimentary a review for a specialist, this section establishes Cockell's book as a valuable resource for all astrobiologists, including advanced biology majors and graduate students.
With the background of life laid out (all astrobiologists can appreciate that it takes nearly 130 pages to define “life”), the book begins to paint the backdrop for the scene upon which life developed. The origin of the Universe and Solar System are laid out with less of a classic historical theme but rather through the focus of astronomy and astrochemistry. This treatment naturally leads to a review of early Earth. As this chapter is closer to my own background, I felt the chapter covered the main topics (differentiation, theories of moon formation, early crust, etc.), but the treatments were short. Without additional lecture, assigned reading material, or other activities, it would be challenging for a non-geologist to draw a full picture of early Earth evolution. However, as an upper-level textbook, it is more important to cover the swath of the current state of the field, as it would be expected that the students would undertake additional effort to fully realize the material. In that regard, the textbook fulfills its goals.
The next chapters move through the evolution of Earth's biosphere by following the dual paths of the linear trajectory toward the present as well as the oddball events (e.g., Snowball Earth) that have punctuated our planet's history. Beginning with Chapter 16, the focus shifts to the broader Solar System, starting with a general discussion of habitability then looking toward Mars. The text then follows a natural progression through the jovian moons and spreads out to the exoplanets. In summary, the text covers the spectrum of potential astrobiological targets after a thorough picture of the evolution of life on Earth. The final chapters discuss the current paradigms for the search for extraterrestrial life and the impact of humans on our own planet. The treatment is not as detailed as Gale's text and seems as an afterthought on a text that is so rich on developing the scientific underpinnings of astrobiology.
Cockell's textbook is also quite valuable as it incorporates the add-ons that have shown to be useful for organizing chapters for student success. Each chapter begins with a box of Learning Objectives clearly defining the basis of the chapter. The color illustrations are simple but effective and strike a good balance of setting off the text without being overbearing. Interspersed through the text are “Debate Points” that instructors could incorporate in a flipped-classroom setting or at least use to encourage active debate. References at the end of the chapters are up to date and thorough. In addition, the companion Web site hosts lecture slides and other resources. If nothing else, be sure to download the Astrobiology Periodic Table. I was able to use it to have a discussion with my 10-year-old daughter, and she followed it quite well!
Comparing these two textbooks, the question remains, “Is Astrobiology mainstream enough to serve as an undergraduate general science elective, or is it best as a graduate course that could draw in students from multiple disciplines who could serve as peer teachers along with the instructor?” The answer is both. The ongoing excitement and popularity of Solar System—and exoplanet—exploration provides ripe fodder to draw students in, and there is clearly a wealth of topics that can be broached. In fact, most of the chapters in both books could be enhanced by merely following the current news as well as the journals. Cockell's Astrobiology: Understanding Life in the Universe is a high-level but entirely approachable textbook that will likely be used in many universities.