Book excerpt: Mars Geological Enigmas: From the Late Noachian Epoch to the Present Day presents outstanding questions on the geology of Mars and divergent viewpoints based on varying interpretations and analyses. The result is a robust and comprehensive discussion that provides opportunities for planetary scientists to develop their own opinions and ways forward. Each theme opens with an introduction that includes background on the topic and lays out questions to be addressed. Alternate perspectives are covered for each topic, including methods, observations, analyses, and in-depth discussion of the conclusions. Chapters within each theme reference each other to facilitate comparison and deeper understanding of divergent opinions. - Offers a transchronological view of the geological history of Mars, addressing thematic questions from a broad temporal perspective - Discusses outstanding questions on Mars from diverging perspectives - Includes key questions and answers, as well as a look ahead to which puzzles remain to be solved