The film Jurassic Park, based on Michael Crighton’s extraordinary 1990 novel, gave us accessible dinosaurs and spawned an industry in cuddly T-Rexs, Dino Babies and fierce plastic models essential to every toybox. While the name Jurassic has remained in everyone’s verbal toolkit ever after, few knew what it meant other than some time very long ago. In truth, it’s still a puzzle. Try asking anyone who knows their geological timescale and you’ll soon be confounded by Eras, Periods, Epochs, a blizzard of strange names ending in -zoic, -cene, -ian or worse, and mind-numbing depths of time. I had the timescale on my wall for years and never managed to master it.