Helen Czerski works at the forefront of marine science, and in her new book offers fascinating insights into the defining feature of our planet – its ocean. Join her as she explores the passengers and voyagers who live and travel across the ocean; visits the depths to  encounter active volcanoes and an upside down waterfall; and examines the history of human fascination with the ocean.

3. The Question of Salt. Helen takes a look at how ocean dwellers stay hydrated despite their salty home.