This page contains updates/revisions to the text, and reflects changes made after August 2023. The most recent changes appear at the top of the page.
August 2023: Section 3.2: clarified the reasons for density differences in granite and basalt. Section 5.2: corrected mistake reversing the proportions of ice vs. groundwater on Earth; added text regarding the comet/meteorite hypothesis for the origin of the oceans. (Thanks to Emily Wright for those suggestions.)