While some Earth-like worlds can generate significant O2 only by biology, “waterworlds” and “desert worlds” can build up O2 even without life because of chemical changes from atmosphere loss to space.
Interiors
Posted inEditors' Highlights
What Happened When the Lithosphere of Venus Broke?
Although Venus does not have plate tectonics today, previous episodes of intense tectonic activity could have resulted in a distribution of crustal thickness and age resembling the plate we see today.
Posted inNews
Freezing Mars's Core—in the Lab
Mars's core, widely thought to be at least partially molten, may eventually solidify completely, and researchers have turned to lab experiments to find out how.