What do iron deposits, fossils, and radioactive meteorites have in common? They’re all keeping records of our geologic history, the unimaginably long period of time that our Earth has been swinging around the sun. In this episode, we’ll look back into geologic time, discovering what we know, how we know it, and what it all means. Introduction: Michigan's Upper Peninsula 00:00 What is geologic time? 0:39 How do we study geologic time? 3:06 How old is Earth, and how do we know? 7:43 Review and Credits 10:34 Sources: https://docs.google.com/document/d/1RpwM8ZQPFk_DkzMJjMdtRrNGrJSNJ7FbgmQybSZ2Cqo/edit?tab=t.0 Check out our CC Geology Extracurricular Playlist here: https://www.youtube.com/playlist?list=PL8dPuuaLjXtOmqnkvEtNVOrm0eaIjFjJ7 *** Support us for $5/month on Patreon to keep Crash Course free for everyone forever! https://www.patreon.com/crashcourse Or support us directly: https://complexly.com/support Join our Crash Course email list to get the latest news and highlights: https://mailchi.mp/crashcourse/email Get our special Crash Course Educators newsletter: http://eepurl.com/iBgMhY Thanks to the following patrons for their generous monthly contributions that help keep Crash Course free for everyone forever: b.sav, Martin G. Diller, Scezumin, Johnathan Williams, Mike Cumings, Jr., Allison Wood, NassauLinda, Chuck Smith, Katrix , Jason Terpstra, Jennifer Wiggins-Lyndall, Dalton Williams, DexcilaDou, Chelsea S, Matthew Fredericksen, AThirstyPhilosopher ., Scezumin, AThirstyPhilosopher ., Emily Beazley, Andrew Woods, DexcilaDou, Roger Harms, UwU, Johnathan Williams, Kyle & Katherine Callahan, Stephen Akuffo, Jennifer Wiggins-Lyndall, Shruti S, Barbara Pettersen, Gina Mancuso, Dalton Williams, Toni Miles, Mike Cumings, Jr., Quinn Harden, Michael Maher, Jason Terpstra, Matthew Fredericksen, Rie Ohta, Chuck Smith, Allison Wood, David Fanska, Katrix , Chelsea S, b.sav, Brandon Thomas, Steve Segreto, Elizabeth LaBelle, Reed Spilmann, Leah H., NassauLinda, Kevin Knupp, Martin G. Diller, Ken Davidian, oranjeez, Laurel Stevens, Jason Buster, Alan Bridgeman, Samantha, Jason Rostoker, Breanna Bosso, Caleb Weeks, Joseph Ruf, Ken Penttinen, Luke Sluder, Wai Jack Sin, Siobhán, Krystle Young, Matt Curls, Stephen McCandless, Eric Koslow, John Lee, Tandy Ratliff, Perry Joyce, Sarah & Nathan Catchings, Rizwan Kassim, Katie Dean, Ian Dundore, team dorsey, Erminio Di Lodovico, Barrett, Trevin Beattie, Bernardo Garza, Kristina D Knight, Nathan Taylor, Emily T, Constance Urist, Jennifer Killen, Thomas, Alex Hackman, Triad Terrace, Indija-ka, Evol Hong, Scott Harrison, Pietro Gagliardi, Les Aker, Tanner Hedrick __ Want to find Crash Course elsewhere on the internet? Instagram - https://www.instagram.com/thecrashcourse/ Facebook - http://www.facebook.com/YouTubeCrashCourse Bluesky - https://bsky.app/profile/thecrashcourse.bsky.social CC Kids: http://www.youtube.com/crashcoursekids