On The Edge Of The World - James Jackson's 1995 Christmas Lectures 1/5

In his first lecture, James Jackson explores how we found out what Earth is made of and where we come from. Watch all the lectures in this series here: https://youtube.com/playlist?list=PLbnrZHfNEDZzN4JcqnWDW02rO0gJU7qBx&si=lmo1ZuOBkecGK5Rq Watch our newest Christmas lectures here: https://www.youtube.com/playlist?list=PLbnrZHfNEDZyQJZLPMjwEoOLdkFBLU2m1 This was recorded on 1 Dec 1995. -- 2025 and 2026 mark 200 years of the Royal Institution Christmas Lectures — a world famous series showcasing science, curiosity, and mind-blowing demos, and started by the legendary Michael Faraday himself. To celebrate, we're unlocking the archive. Every week, we’ll upload a classic lecture to our YouTube channel — some not seen since they aired on TV. Sign up as a Science Supporter and get early access here: https://www.youtube.com/channel/UCYeF244yNGuFefuFKqxIAXw/join -- From the 1995 programme notes: It is a daunting task: the centre of the Earth is more than 6,000 km away and we can't dig a hole that deep! We have to look for clues: and they may be unexpected ones. What can we learn from a large earthquake in Bolivia that was felt in Canada, and made the Earth wobble for months? What can we see in volcanoes, which bring material from deep underground to the surface? The early navigators knew that the Earth's magnetic field changed with time, but how does that help us to know that the Earth has a core made of liquid iron? What clues are provided by our neighbours in the solar system? We have visited or flown past some of them, and some of them visit us in the form of meteorites. Such clues tell us what the Earth is made of, that it is layered, and that it is very old – it formed about 4,500 million years ago. But that is not all. As we go deeper into the Earth it gets hotter and this encourages all crystalline materials, including rocks, to flow. The flow happens in the solid state and is called creep: the rocks do not have to melt to do this. The same rocks which deep down are hot and weak can be very strong at the surface, where they are colder. So the Earth has a strong outer lid above a weak, creepy inside. This dual behaviour is the key to how the Earth can be so mobile. -- About the 1995 CHRISTMAS LECTURES Catastrophes such as volcanic eruptions, earthquakes, climate change and sea level rise are starting to have a huge impact on our lives as our population increases and we colonise every available corner of the world, particularly the coastlines. Yet at the same time these phenomena, which are disasters to us, are a natural part of the way the Earth behaves. We can use them as tools to see deep inside the Earth, to see how the planet is put together, and how it changes with time. Our understanding of how the Earth works has just undergone its biggest change since we realised that the Earth orbited the Sun. Scientists used to see the Earth as a planet whose surface had been the victim of random and unexplained events, such as mountain building and changing climate. Now we know that what we see at the surface is caused by vigorous motions deep inside the Earth — motions that are slow compared with our lifetimes, but are very fast compared with the life of the Earth itself. Far from living on a dead lump of rock in Space, we are living on jelly, but didn't realise it! These lectures trace the story of how and why our views changed — from a fumbling suspicion that continents had moved around, through a detailed reconstruction of how the pieces fit together, to the present, where we can measure the motions directly and see them going on. It is a story in which chasing a clue to one puzzle has often produced unexpected results and paradoxes. Find out more about the CHRISTMAS LECTURES here: https://www.rigb.org/christmas-lectures --- Join this channel to get access to perks: https://www.youtube.com/channel/UCYeF244yNGuFefuFKqxIAXw/join Subscribe for regular science videos: http://bit.ly/RiSubscRibe The Ri is on Twitter: http://twitter.com/ri_science and Facebook: http://www.facebook.com/royalinstitution and TikTok: https://www.tiktok.com/@ri_science Listen to the Ri podcast: https://podcasters.spotify.com/pod/show/ri-science-podcast Donate to the RI and help us bring you more lectures: https://www.rigb.org/support-us/donate-ri Our editorial policy: https://www.rigb.org/editing-ri-talks-and-moderating-comments Subscribe for the latest science videos: http://bit.ly/RiNewsletter Product links on this page may be affiliate links which means it won't cost you any extra but we may earn a small commission if you decide to purchase through the link.