Chalk, limestone, shale, and sandstone are all examples of sedimentary rocks. All these different sedimentary rocks are formed from the broken remains of other rocks that become joined together.

For most organisms on Earth, rocks are objects, not food. But for one oddball microbe, desert limestone seems to have been on ...

Fungi can bore through rocks and leave behind tubes, and some types of cyanobacteria also thrive off limestone or marble. It is unlikely that the mystery organisms were cyanobacteria—they need ...