People often talk about being descended from apes. But go back a bit further and we have a more unlikely ancestor – fish. Improbable as it may sound, the creature that gave rise to every bird, reptile and mammal on Earth today lived a fully aquatic life. So how did it switch to life on land? And how hard was it to swap swimming for walking and breathing fresh air? That’s what CrowdScience listener Pierre in France wants to know, and what Marnie Chesterton is in Scotland to find out. She goes fossil hunting with members of the TW:eed Project team, as they try to uncover remains of creatures that are crucial in helping solve the puzzle of terrestrial life. She also discovers the landscape these early ancestors walked into – an alien and relatively empty world completely different to what we see today - where grass and flowers were yet to evolve. But not everything in this story is preserved in rock. Marnie goes to see a living relic of this period of evolution, and finds out what it can tell us about possibly the most important event in the history of our species. Do you have a question we can turn into a programme? Email us at crowdscience@bbc.co.uk Presenter: Marnie Chesterton Producer: Anna Lacey (Image: Artists impression of underwater environment of Carboniferous swamp depicting a rhizodont; a large predatory fish. Credit: Mark Witton)