In short · Summary by AI
This Crash Course Geology episode explains how fossil fuels formed from ancient organisms and why they are non-renewable and environmentally harmful. It presents geothermal energy from Earth's internal heat as a renewable, emissions-free alternative that is abundant but hard to access in many places.
- Fossil fuels like oil, coal, and natural gas formed from plankton and plant remains buried over millions of years under specific conditions.
- Oil and natural gas form when organic ooze becomes organic shale, then kerogen, then hydrocarbons and methane under rising heat.
- Coal formed mostly about 350 million years ago during the Carboniferous period from peat compressed by heat and pressure.
- Fossil fuels are non-renewable and extraction methods like fracking and mining cause pollution, habitat damage, and health risks.
- Geothermal energy comes from Earth's internal heat, which is easiest to tap near volcanic regions and tectonic plate boundaries like Iceland.
- Humans have used geothermal heat for thousands of years for cooking and later for electricity, with a plant in Tuscany running for over 100 years and about a quarter of Iceland's electricity coming from it as of 2023.
- Geothermal power produces no emissions or water use and is available constantly, unlike solar or wind.
- Heat pumps in deep boreholes can reach geothermal energy in non-volcanic areas, but the upfront cost and drilling requirements limit wider adoption.
- 0:00St. Patrick's Cathedral Geothermal Wells
- 0:44Our Reliance on Energy
- 1:23How Oil Forms Underground
- 3:16How Coal Forms Over Time
- 4:35Problems with Fossil Fuel Extraction
- 5:16Introducing Geothermal Energy
- 6:32Geothermal Energy Through History
- 7:50Abundance and Access Challenges
- 9:13Geothermal Use Around the World
- 9:54Future of Energy Transition
St. Patrick's Cathedral Geothermal Wells
0:00Ah, New York City. The home of Broadway, the $2 slice, and this, [music] St. Patrick's Cathedral. The nearly 150-year-old church is truly something to behold. With its sky-high spires, stained glass windows, and massive pipe organ, it's a favorite destination for tourists. I guess the shirt gave me away, huh?
0:15Yeah, I'm from California. But I do a great Robert De Niro. Yeah, I'll work on it. All right, Dwayne. But there's something else amazing about the cathedral. Around the church, 10 wells are dug deep within the earth. Some as far down as 670 m. That's more than six times deeper than the height of its spires.
0:31Why? For energy. Piped up straight from the earth. Hi, I'm Sage, and this is Crash Course Geology.
Our Reliance on Energy
0:44When we need energy, where do we turn? When it comes to our bodies, we eat plants and animals. But when it comes to fueling our cars, heating our houses, or powering our studio lights and video cameras, we need more energy, like a lot more. For the past 150-ish years, we've mostly powered our world with fossil fuels, things like oil, coal, and natural gas.
1:04They're compounds made of algae, plant, and animal remains from millions of years ago. That's right, million-year-old dead stuff powers my toothbrush, TV, and motor scooter. Catch me yelling this to everyone as I scoot around Long Beach. But how do we get fossil fuels? Well, when most living things die, they decompose, breaking down into simple compounds.
How Oil Forms Underground
1:23But if they're buried in just the right conditions, amazing things start to go down. Take oil, for example. To start, we've got plankton, those tiny life forms that drift around in bodies of water. In still water without a lot of oxygen, it's hard for them to decompose. So instead, dead plankton accumulate at the bottom, mixing with clay to become organic ooze.
1:46And earth starts to work its magic. As the ooze gets buried deeper and deeper, the pressure squeezes out water, transforming it into a rock known as organic shale. And if that rock is buried deep enough, the rising temperatures transform it again into a waxy, energy-dense substance called kerogen. Under Earth's surface, things can get pretty hot.
2:05If temps down there climb past 90° C, kerogen breaks down into small oil molecules known as hydrocarbons. At even higher temperatures, the oil molecules break down even smaller to form natural gas. The natural gas we use for fuel is mostly made of methane, by the way. Once they're formed, oil and natural gas can percolate up toward the surface.
2:26Some oil might even bubble up in ponds called oil seeps. But other pockets get trapped underground by impermeable layers of rock and settle into reservoirs, which we can tap for fuel. Now, coal, on the other hand, forms a bit differently. Nearly all the coal on Earth right now formed about 350 million years ago.
2:48At that time, Earth was covered in plants. A super rainy climate gave us tons of tropical areas with wet forest floors. Those swampy areas were low in oxygen, which meant that living things didn't decompose as much. At the same time, all the continents were coming together in a geologic mashup that would eventually create the supercontinent Pangea.
3:09As tectonic plates collided, they raised towering peaks and formed plunging basins, the perfect collection point for layers upon layers of dead plant matter. The intense buildup of plants eventually transformed into peat, an energy-rich substance resembling soil. Peat has long been an energy source for humans.
How Coal Forms Over Time
3:28We've used it for cooking and heating for thousands of years. But if peat is buried deep enough, the Earth's heat and pressure concentrate the plant's carbon and hydrogen into an even more energy-dense brittle rock called coal. This coal-creating time was only about 60 million years long, just a small slice of our planet's 4.6 billion year history.
3:48It became known as the Carboniferous period, meaning coal-bearing. Since then, conditions have rarely been exactly right to create more. Once we use up our ancient reserves of coal, it'll be gone, possibly forever. Wow, I think I'd actually be down to get a lump of coal for Christmas this year. You're real?
4:09Dairy-free, right? Oh my god, thank you. This coal conundrum captures one of the big problems with fossil fuels. They're non-renewable, which means it's possible to use them up or for them to become so hard to extract that it's not practical to keep using them. Even though the Earth can make more coal, oil, and natural gas, it can't do it on a human timescale.
4:33It would take millions of years to restore what we've consumed. And even if they were infinite, there are issues with how fossil fuels are extracted, too. When more easily accessible reservoirs of oil and natural gas run dry, we have to resort to tactics like fracking, which uses high-pressure water, chemicals, and sand to break up impermeable rock.
Problems with Fossil Fuel Extraction
4:54This can have a variety of harmful effects from air pollution to habitat degradation and potential health issues for people living nearby. As for coal, mines can cause a whole host of problems, too, like sinkholes, erosion, water contamination, and damage to plant and animal habitats. That's not to mention the human cost of environmentally hazardous processes and the impacts on Earth's climate.
Introducing Geothermal Energy
5:19You can learn much more about the effects of fossil fuels in Crash Course Climate and Energy. So, there are lots of reasons to break up with fossil fuels and find other sources of energy. And Earth might hold one of the keys to powering our future more sustainably. Geothermal energy. Geothermal energy comes from the heat under Earth's surface.
5:38The inside of our planet is super hot. It's still holding onto heat from the collisions that likely formed it. Then there's the decaying radioactive elements in the core and mantle and all the hot magma and volcanic activity in there. There's a lot of energy stored beneath our feet. And no, Dwayne, I'm not saying that the floor is lava.
5:57You're You're good, dude. But, how do we harness it? We can most easily tap into geothermal heat near volcanic regions where pockets of molten rock have risen up into the crust. The magma heats up water that collects in cracks and pores in the crust, creating geothermal reservoirs. The heated water can sometimes rocket through the surface as jets of steam or sizzling geysers like a geologic water park.
6:20Or, it can bubble up like hot tub jets into a hot spring. A lot of volcanic activity happens near the boundaries of tectonic plates or places where the crust is really thin. That lets hot mantle rock and blobs of magma sneak up closer to the surface. Like, Iceland is an island that sits right on the mid-ocean ridge, an underwater mountain range where two tectonic plates are pulling apart.
Geothermal Energy Through History
6:43This makes it a great place to harness geothermal energy. And this kind of energy is nothing new. Humans have been using geothermal energy to power their lives for thousands of years. Early hominins in East Africa might have used hot springs to cook their food. And people in Iceland still do today, like with this traditional hot spring bread.
7:01You're telling me I can experience the wonders of the Earth and eat delicious bread? Sign me up. But, it didn't stop there. We started using geothermal energy to power electricity over 100 years ago. At a power plant in Tuscany that's still operational today. And as of 2023, about a quarter of Iceland's electricity is powered by geothermal energy.
7:21That leads us to one of the greatest points in favor of geothermal. By running geothermal steam or water through pistons and turbines, we can generate electricity without producing any emissions or using up any water. Because of the abundance of heat and volcanic activity under the Earth's surface, geothermal energy is renewable.
7:43And unlike other renewable energies like solar or wind power, geothermal energy is available all the time, rain or shine. And did I mention the abundance factor? I know I did, but I feel like it's worth emphasizing. Some researchers think that just 0.1% of the heat produced by the Earth's core would be enough to meet all of humanity's energy needs for the next 2 million years.
Abundance and Access Challenges
8:062 million years. So, what what what's the hold up? Why aren't we already running the Earth on you know, the Earth? The biggest challenge is tapping into all that energy. We can't exactly dig down to the Earth's core. While geothermal energy can be pretty accessible in volcanic regions, it's a lot tougher in places where you have to dig deep below the surface.
8:30To do it, you have to install heat pumps in deep boreholes in the ground. The heat pumps send water and other substances way down into the crust to capture heat. Then they transport it up to the surface, where we can use it to cook, heat buildings, or power electricity. Even in places as unvolcanic as Ohio or New York City.
8:49In fact, heat pumps can give us access to geothermal energy nearly anywhere. But they're expensive up front, and not every location can accommodate the big drills required to put them in place. Add the fact that most folks don't even know what geothermal energy is, and you can see why there isn't a heat pump on every corner.
9:07So, it'll take a lot more work to make the infrastructure for geothermal energy [music] accessible to everyone. But in places like Italy, Indonesia, and the western US, geothermal energy is growing fast. It's used for air conditioning in Tuscany, mushroom farming in West Java, and melting snow on roads and sidewalks in [music] Oregon.
Geothermal Use Around the World
9:25There are still lots of opportunities to incorporate this form of energy into our daily lives. Maybe someday you'll warm your hot chocolate with geothermal energy. Cheers, Dwayne. Sorting out our relationship with energy is a complex problem. As humanity's energy needs grow, we need to find alternatives to fossil fuels.
9:45And while it's unlikely that geothermal energy is the solution to all our problems, it could become a key part of the wider effort to live within the capacity of our planet. Geologists today are figuring out how to combine geothermal energy with other renewable sources and strategies, so we can say farewell to fossil fuels for good.
Future of Energy Transition
10:08Next time, we'll learn about the minerals that power our modern world. See you then. Thanks for watching this episode of Crash Course Geology, which was filmed in our studio in Indianapolis, Indiana. It was made with the help of all these beautiful bubbly people. If you want to help keep Crash Course free [music] for everyone forever, you can join our community on Patreon.
More Crash Course transcripts
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- How Often do Asteroids Hit the Earth?: Crash Course Geology #20
- Why Does the US Only Have Two Major Parties?: Crash Course US Government #2
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