Bacteria are in, around and all over us. They thrive in almost every corner of the planet, from deep-sea hydrothermal vents to high up in the clouds, to the crevices of your ears, mouth, nose and gut.

The CT-scanned skull of a 319-million-year-old fossilized fish, pulled from a coal mine in England more than a century ago, has revealed the oldest example of a well-preserved vertebrate brain. The ...