91av

Why we can't announce life on Mars (yet); The Romans' impact on the British economy; Link between exercise and your microbiome

12 September 2025

About this episode

Episode 320

Was Mars once home to alien life? The evidence is stronger than ever, since NASA’s discovery of rocks marked by patterns similar to those made by microbes on Earth. Found in an area now named Bright Angel, these rocks give us a tantalising insight into Mars’ ancient past - but just how definitive is this finding?

It’s long been thought that when the Roman Empire withdrew from Britain in the early 400s, the result was chaos and economic collapse. But a new archaeological discovery suggests that’s not the case. Signs show a boom in the ancient metalworking trade around that time. Do we need to rethink this period of our history entirely?

We’re constantly discovering more and more ways to boost our microbiome and improve our health – everything from eating more fibre and fermented foods to having pets and embracing dirt. And now there’s something else to add to the list: weight lifting. After being put on a weight training programme, a group of sedentary adults showed a surprising uptick in beneficial gut bugs. But how are the two things connected?

Chapters:

(00:00) Intro

(01:19) Strongest evidence for past life on Mars

(14:55) The Romans impact on the British economy

(23:19) Link between exercise and your microbiome

Hosted by Rowan Hooper and Penny Sarchet, with guests Mike Marshall, Mike Tice and Sanjeev Gupta.

To read more about these stories, visit /
Get your ticket for 91av Live here:

Learn more about your ad choices. Visit

Sign up to our weekly newsletter

Receive a weekly dose of discovery in your inbox. We'll also keep you up to date with 91av events and special offers.

Sign up
Piano Exit Overlay Banner Mobile Piano Exit Overlay Banner Desktop