Previous: The 10 Oldest Fossils, and What They Say About Evolution
Next: Why Do My Ears Pop?



View count:264,720
Last sync:2023-01-23 05:15
Rocks are more than just rocks, they're the key to Earth's history!

Hosted by: Hank Green
Support SciShow by becoming a patron on Patreon:
Dooblydoo thanks go to the following Patreon supporters -- we couldn't make SciShow without them! Shout out to Justin Ove, Andreas Heydeck, Justin Lentz, Will and Sonja Marple, Benny, Chris Peters, Tim Curwick, Philippe von Bergen, Patrick, Fatima Iqbal, Lucy McGlasson, Mark Terrio-Cameron, Accalia Elementia, Kathy & Tim Philip, charles george, Kevin Bealer, Thomas J., and Patrick D. Ashmore.
Like SciShow? Want to help support us, and also get things to put on your walls, cover your torso and hold your liquids? Check out our awesome products over at DFTBA Records:
Looking for SciShow elsewhere on the internet?
[SciShow intro plays]

Hank: When you look at a rock, what do you see? Well you probably see what I see... a rock: grey, brown, maybe a few sparkles. Nothing too exciting. But to 18th-century geologist James Hutton, rocks were more than just rocks. Instead, they were the keys to Earth’s history -- billions of years of stone, shifting, melting, crunching, twisting, and re-forming. A history that he discovered in a time when most people believed that the world was 6,000 years old.

James Hutton was born in Edinburgh, Scotland on June 3, 1726. He was a bit of a floater, studying at several universities throughout his youth. This wasn’t that big a deal -- he had a pretty large inheritance and several farms, and was able to live comfortably without finding a specific trade. According to his teachers, he didn’t like math very much, but he did have a strong interest in chemistry. He qualified as a doctor, and wrote his medical dissertation on the circulation of blood, which he believed -- correctly, but for the wrong reasons -- was constantly being destroyed and renewed.

Eventually, Hutton decided that he didn’t really want to pursue medicine. He spent some time on his farms, then moved back to Edinburgh in 1768, and began to develop his ideas about geology -- which also involved renewal and recirculation.

In Hutton’s time, a lot of people believed that Earth was shaped by catastrophes like the ones in the Bible. But Hutton thought Earth actually went through a constant cycle of destruction and renewal. He proposed that rocks and soil are eroded and swept into the sea, then compacted into bedrock before being twisted and turned by enormous pressure A few years after he first came up with this theory, Hutton discovered evidence for it in a few different rock formations. The most famous of these discoveries was at Siccar Point, a cliff on the eastern coast of Scotland that features layers of red sandstone and greywacke -- a darker type of sandstone.

The layers were sitting on each other, but they were also running in layers perpendicular to one another, in what we now call an angular unconformity. He hypothesized that only great amounts of time and great pressure could have offset the rocks -- much longer than 6,000 years. And, as we know now of course, he was right. This feature at Siccar Point -- and several others around Scotland -- are called Hutton’s Unconformity in his honor.

He also discovered that granite was an igneous rock, by observing tendrils of granite that had made their way into rock like sandstone -- which he realized could only have happened at very high temperatures. Hutton believed that this was strong evidence that there was molten rock below the surface of the Earth, and that this molten rock was constantly pushing outward and then melting again. He published his findings in a paper in 1788, but his theories didn’t always gain traction because they often contradicted the idea that Earth was 6,000 years old. Plus, a lot of other scientists’ geological theories incorporated the great flood described in the Bible. Hutton’s ideas did not.

But a lot of his work turned out to be accurate, even though he didn’t have access to technologies like carbon dating, which would have put actual numbers on the ages of rocks. Hutton also paved the way for future scientists, like 19th-century British geologist Charles Lyell, to develop a theory called uniformitarianism.

Uniformitarianism is the idea that the processes that shape the world now, also shaped it in the past. So, scientists can work backward and figure out what happened in the past. By assuming that natural laws function in the same way across space and time, we don’t need major catastrophes to explain how Earth formed. Instead, we can show that it’s the result of slow processes over enormous spans of time.

Thanks to Hutton, the picture of our world got a lot more complex. He was wrong about some stuff, but many of his ideas helped shaped geological concepts that we still use today. Not too bad for a guy who’s famous for saying that the Lord should pity the backside that is -- and I quote -- “clagged to a head that will hunt stones.”

Thanks for watching this episode of SciShow, which was brought to you by our patrons on Patreon. If you want to help support this show, just go to, and don’t forget to go to and subscribe!