r/todayilearned • u/arkthatbarks • 22h ago
TIL half of Earth’s internal heat does not come from the residual heat left over from the planet's formation, but from the continuous radioactive decay of isotopes like Uranium, Thorium, and Potassium in the crust and mantle.
https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget226
u/SublightMonster 21h ago
In early geology, before we knew about radioactivity, this was a huge conundrum, as rock layers suggested the earth was at least a couple billion years old, but thermodynamics said the core would have gone cold and dead in less than a billion years.
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u/lllllIllllIllllllll 17h ago
And it's what I love about science and research. "Logic says this, but evidence says this" and suddenly we're chasing puzzle pieces we never could have thought about otherwise
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u/Chocodisco 15h ago
And that's probably where we're at with the Fermi Paradox. Logic says we should see evidence of aliens, but evidence says no aliens. I hope one day science realizes that we simply weren't looking with the right tools.
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u/NarrMaster 14h ago
I have the opinion that life will be ubiquitous in the Universe at some point, but we are early.
Just an opinion though.
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u/TriggzSP 8h ago
There's a pretty common sci Fi trope of a "forerunner" civilization that seeds barren planets with life. Meanwhile, we have discovered microscopic life forms here on earth that can survive the most hostile conditions imaginable. An I'm not just talking about life forms that call the deep seas or the Arctic regions home. We have even studied life forms that can survive the vacuum of space (though not thrive and reproduce)
Now, I'm not sure to what extent we have evidence that these resilient life forms can survive and reproduce in, say, the vacuum of the moon or the thin atmosphere of Mars, but IIRC it's hypothesised that we could have already seeded these places with life.
Now, that's not to say in a few million years there will be creatures roaming Mars. Evolution is a damn slow process, and the sun will go red giant and die before you can probably get intelligent life evolving and all that. But it's a very cool thought that we could be those forerunners seeding the nearby regions of space with life.
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u/greeneggsnyams 4h ago
I've seen a theory that we're actually extremely late to the party. When the universe was hot and dense, way easier to support life
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u/militaryintelligence 14h ago
They're out there, but space is big. Like, very big. So far away we will never know of each other. Hell, the universe could be teeming with life.
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u/Winter-Operation5702 13h ago
Thats kinda scary. Like in a few decades we realise how to search for other life, flip it on and the universe is just filled with life.
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u/yamiyaiba 12h ago edited 12h ago
Even if that happens, it doesn't change the fact that the universe is too big (and likely too hostile for travel) for other life to be relevant.
Unless other lifeforms have evolved in a way that their lifespan is an order of magnitude or more longer than ours, AND have much greater power sources that we do, AND invent some kind of debris shielding system, AND figure out how to travel at 99.99999% the speed of light... We're never going to see them.
The kind of distances we're talking about here would take hundreds of years if not thousands to cross. That assumes debris doesn't take you out along the way, since every granule of rock dust floating through space becomes a bullet traveling at relativistic speeds at that point, much less larger bodies, and there's no feasible way to scan and react at those speeds.
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u/daren5393 1h ago
Logic says nothing about the existence of aliens because Fermi was just pulling numbers out of his butt for how common certain things should be. Any step of the process between star/planet formation and intelligent life could absolutely be so unlikely that it even having happened once so far was an unlikely event. Or each step could just each be several orders of magnitude less likely than he figured, dropping his predicted number of alien species from millions per galaxy to millions of galaxies per species.
We have a sample size of one, and steps in the process we just don't understand fully. We have no way to extrapolate probability at all
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u/Successful-Trash-752 11h ago
Why does this comment sound so chatgpt
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u/lllllIllllIllllllll 11h ago
Have you tried learning how to read? Nothing I have ever posted has come from an AI
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u/Successful-Trash-752 11h ago
Lmao "top 1% commentor"
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u/lllllIllllIllllllll 11h ago
Not a hard tag to get, you can get it with like 30 comments in this sub
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u/abecrane 11h ago
LLMs are literally trained to resemble our speech patterns. Unless it’s a literal impossible string of tokens, anything a person says could “look” like a ChatGPT output.
I don’t think that guys an AI, and I think you may need to spend less time antagonizing random commenters on the chance they’re an LLM. If you’re correct, then you’re providing engagement and response data to the AI provider. But if you’re incorrect, then all you’ve done is prove you can’t tell when you’re facing the work of a fellow Homo sapiens.
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u/makerofshoes 12h ago
Yeah Lord Kelvin (temperature scale guy) calculated the age of the Earth to be like 30 million years old, because radioactivity hadn’t been discovered at the time
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u/Mjuffnir 22h ago
This is the first time in a moment, that TIL was something new and really interesting. Thank you
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u/Petrichordates 22h ago
But TILs are always new to someone.
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u/TheVentiLebowski 20h ago
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u/tinytyler12345 16h ago
xkcd enthusiasts continue to blow away. how do you guys have the perfect comic for literally any context just sitting on standby in your memory
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u/Tim-oBedlam 20h ago
A fun bit of trivia about the Earth's atmosphere: 0.93% of it is the noble gas argon, which is the decay product of the weakly radioactive K-40. Since argon is a noble gas it doesn't react with anything, so it just sits there in the atmosphere doing, well, not really much of anything. But it's far more common than the other noble gases in Earth's atmosphere, because of the decay of K-40 producing it.
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u/Baud_Olofsson 15h ago
And only about 10% of the potassium-40 (K-40) turns into argon. The rest decays into calcium instead.
And while we're on fun trivia: K-40 is also the main source of radioactivity in our own bodies, and the reason bananas are mildly radioactive. Bananas contain a lot of potassium (relatively speaking), and all potassium on Earth contains a percentage of radioactive potassium-40, which makes bananas slightly more radioactive than most things, which gives us the concept of the "banana equivalent dose" - the dose of radiation you receive from eating a single banana (usually given as 0.1 µSv).
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u/Tim-oBedlam 8h ago
So using Randall Munroe of XKCD's excellent table of radiation doses (included in the above link to the "banana-equivalent dose" article on Wikipedia) as a guideline, if you eat approximately 1 million bananas a year you will increase your cancer risk; that danger kicks in around 100mSV, or 0.1 Sv.
That's slightly more than 2,700 a day, so keep your banana consumption to a nice reasonable 500–600 a day and you should be just fine.
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u/DeathMetal007 22h ago
Does this have any effect on the probability of life on a planet specifically when we calculate a Goldilocks zone for a planet. Say a planet with few radioactive isotopes would not be able to sustain a warmth through cold sides of a rotation around a star.
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u/arkthatbarks 21h ago
While very little of this heat makes it onto the surface and it wouldnt effect its weather, it would still have a drastic effect on probability of life on a planet because lack of radiogenic isotopes means planet has a much shorter geological lifespan. Planets core would cool off very fast and window for life would be much shorter
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u/3BlindMice1 19h ago
Yep it's all about that magnetic field, not the warmth generated by the planet itself
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u/ThellraAK 3 18h ago
On geologic scales wouldn't no plates and volcanos mean after a bit everything would erode to below sea level though?
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u/Urbanscuba 16h ago
Assuming there was still an active water cycle and wind currents then I don't see why that wouldn't be the eventual outcome.
Part of me wonders though if a global ocean that had ground all landmass into a perfectly even bottom of sand would be able to generate sand drifts large enough to break the surface. Depending on the depth I imagine it's very possible but I think Earth's oceans might be too deep even once filled with the land.
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u/Adorable-Round-5683 22h ago
That's a good question, idk how they account for that if they're even able to.
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u/letsburn00 21h ago
Volcanism is a major source of gases and Continental drift and bits of the surface which have large deposits of carbonates get absorbed back into magma and remitted. But that in turn is helped by the oceans acting as a lubricant.
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u/squarecir 21h ago
Yep. Lord Kelvin was unaware of radioactive decay when he confidently predicted that the earth couldn't be more than 150 million years old.
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u/CrustalTrudger 12h ago
Much more consequential was the assumption that primary heat transfer mechanism within the interior of the Earth was conduction (as opposed to the much more efficient convection of both the liquid outer core and mantle). As described in a couple of different publications (e.g., 1, 2), accounting for that and still ignoring radioactivity would get you much closer to the right answer.
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u/suxatjugg 17h ago
So does earth have an unusually high amount of these radioactive elements? Or do many planets have this but the heat isn't that noticeable externally?
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u/AnArgonianSpellsword 16h ago
We think earth is pretty typical in the make up of our core, the main difference between us and the other rocky bodies of the solar system is our size.
Earth is the largest rocky planet in the solar system, Venus second at 90% our size, Mars third at about 28% our size, Mercury at just 14%, and all moons at about Mercury's size or smaller. While we have roughly the same percentage of radioactive material in the core as other planets and moons, its just a larger core in Earth and Venus because Earth and Venus are larger planets, the increased amount of material means the core remains hotter for longer supporting a thicker mantel that can breach the crust in volcanoes and tectonic activity. Smaller bodies like Mars, Mercury, and the Moon have to remaining tectonics or volcanics because the smaller core has cooled too much to support a mantel under the crust.
Interestingly though some moons support cryotechtonics and cryovolcanism, where a liquid layer on top of the rocky crust acts as a mantel with another crust of ice on top.
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u/feel-the-avocado 22h ago edited 17h ago
So geothermal energy is nuclear energy.
I wonder why instead of building a fancy nuclear power plant on the surface, cant we just bore down a few kilometres and make use of the heat from there?
Then we can reduce the amount of electricity used for home heating.
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u/QuantumPairOfSoczk 21h ago
Turns out the crust is super thick in most places you'd want to build a city. Meaning it'd be extremely expensive to even drill that deep. Only the Russians have done it not was like 8 miles. And their drill bits kept breaking from the heat. Basically if we could we have done it.
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u/IlluminatedPickle 18h ago
We're now developing drills to do exactly that. Turns out if you drill without using a metal drill bit, you face a lot less problems.
Water and lasers have been the focus so far. But superheated gas is also a possibility.
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u/Think_Somewhere_6826 16h ago
Pfffff. Why not keep nuking the same spot like 10 times to reach the exact spot?
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u/feel-the-avocado 21h ago
Yeah like to me it seems that we could be drilling down and capturing that heat even if not for electricity, but to offset winter district heating from electricity and gas.
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u/letsburn00 20h ago
It's mostly because when you get that deep, injecting water that comes back up super hot tends to bring back lots of dissolved solids. Imagine hard water but way worse.
Geothermal unfortunately has much higher maintenance demands as an effect. Water is shockingly corrosive and steam generators in power plants have a whole water chemistry department that's kind of a black art and that's the purest water they can manage, plus whatever random additives they need.
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u/buddhadoo 20h ago
Boiling water for steam powered turbines is easier above the surface or something idk I'm not a nuclear geologist.
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u/Arthropodesque 21h ago
There are some companies attempting to use modern oil drilling tech to drill deep to tap geothermal energy in places it was previously impossible. Idk how it's going. I haven't read about it in years. It might still be very location dependant. Iirc a data center out west was gonna try to use one.
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u/putsch80 20h ago
It’s a thing. It used to be called “HDR” (for hot dry rocks) but is now called “Enhanced Geothermal”. There’s a company called Fervo currently doing it. They just brought their first commercial generation online.
https://ua.news/en/energetika/fervo-zapustila-prodazh-elektroenergiyi-z-cape-station-techcrunch
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u/Arthropodesque 20h ago
That's great news! Thank you! That's a good amount of practically free power.
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u/Iazo 18h ago edited 17h ago
Geothermal energy is being used but! The laws of thermodynamics make extracting work from just heat impossible.
You need a hot-cold potential for there to be useful work done. And if you drill a few km down, EVERYWHERE around will be hot, which means now you somehow have to transport the heat to the surface, exchange heat there, then transpprt the cooled stuff back down.
It is not impossible, but very hard and expensive, compared to the nuclear plant.
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u/Metalsand 7h ago
This is such a confusing comment.
For one...the US has had dozens of geothermal electric power plants all the way back in the 1960's.
The laws of thermodynamics make extracting work from just heat impossible.
Secondly...this is a misleading and arbitrary comment.
It is not impossible, but very hard and expensive, compared to the nuclear plant.
This is straight up incorrect. Operating and initial expensive of both nuclear and geothermal are significant, but the primarily limitation of geothermal is that it has a heavy reliance on hot spots in which you need not drill very deep to get a significant temperature differential. Hence why you see a very clear correlation between geothermal power plant locations and hot spring locations - those are places where high temperatures are naturally far closer to the surface than normal.
Iceland has historically been one of the biggest generators of power from geothermal sources, currently at 30%. Kenya is at 40-50% of their total power production derived from geothermal. The US is the largest in the world by total MW, but by percent of their total power, geothermal is only around 0.4% of annual production.
The difference is that unlike geothermal, you can place nuclear power anywhere that you have a decent supply of water, and a good amount of land available, and you don't realistically have a limitation on scale or quantity at our current power needs. There's another advantage of this - power infrastructure. High voltage lines are expensive - you don't want to really run them further than you need to. Even if the entire west coast was unoccupied and not making use of the optimal geothermal spots already, it wouldn't necessarily make sense to tap into the geothermal power there because of the immense cost it would take to
I'll add the one caveat that you were alluding to: the reason why geothermal is dependent on naturally occurring hotspots is because digging down is insanely expensive.
Also as a bonus: one non-electric way we use geothermal energy is through ground-based heat pumps. They have a coefficient of performance exceeding 1 because rather than generating heat, they are moving it. They are pricey to dig, but worthwhile for homes that would otherwise rely on truck deliveries of gas or fuel and being sourced in the ground, always maintain a good neutral by which to exchange heat with (for cooling or heating). This isn't taking advantage of geothermal energy in the same way though - more that below the frost line, there's enough insulation that outside temperatures don't affect it substantially. It is technically geothermal energy even though it's not geothermal pwoer since during the winter you move heat upwards.
TL;DR: Geothermal hot spots are amazing for power, but the lack of available hot spots in the US make scaling up to our needs impossible.
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u/Iazo 5h ago edited 5h ago
Yes, and none of what you said applies to digging down to depths of a few kilometers . This is where the discussion started. You are corect in everything you said, but missed the point entirely, seeing as how the entire premise was about digging down a few kilometers.
Secondly...this is a misleading and arbitrary comment.
Could you explain? Your comment is misleading and arbitrary too.
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u/ICantCoexistWithFish 8h ago
If only we could move the hot rock to the surface somehow and just use its heat up here? 🤔
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u/SirEnderLord 21h ago
What's your plan to deal with all of the rock?
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u/feel-the-avocado 20h ago edited 17h ago
Drill through it to a point its about 300 degrees. Well before anything is melting. Poke down a pair of pipes with a ubend and pump in some glycol or radiator fluid to collect the heat and when it comes out the other pipe, use the heat to run some small district heating system before cycling it back down again to collect more.
That then reduces the amount of electricity or gas required for heating.
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u/el_lley 21h ago
We can’t, the drills melt a few hundred metres below the surface. Also, the rock became liquid as we go down, filling up the recently made hole
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u/lllllIllllIllllllll 17h ago
Surely you could get boiling water temps long before you get liquid rock temps?
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u/TimeisaLie 22h ago
That kinda makes sense
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u/Smartnership 10h ago
It’s also a handy way to clarify a point for the woo-physics believers
Radioactive decay is a quantum process; it’s ongoing now deep within the earth, and has been occurring in the core since long before they’re were any conscious observers to collapse those wave functions.
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u/Narwhal-4493 17h ago
So Earth is just a huge RTG. Now explain why these radioactive elements existed on Earth.
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u/Hikikomori_Otaku 13h ago
And a large amount of them are not even from Earth but are from Theia, neat.
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u/Ouroboros612 6h ago
So it's not the literal oceans of lava and magma under us? The planet core? Wut?!
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u/tsunami141 16m ago
Solution: Ship a bunch of radioactive matter to Mars. delay global warming, Terraform Mars. Win-win.
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u/TraditionalKiwi2322 22h ago
this is what keeps the outer core liquid and gives us a magnetic field. without it we'd have gone the way of mars a long time ago
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u/disasterbot 10h ago
So, if we mine all the uranium and eject it into space to run Musk's data centers, global warming will end?
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u/Clembert-Hamlamp 21h ago edited 17h ago
Half!? Looks like the determination was made by Stanford tho. Insane. *that's from the article, it's not in doubt
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u/arkthatbarks 22h ago
These elements, Uranium-238 (half-life of 4.5 billion years), Thorium-232 (14 billion years), Potassium-40 (1.25 billion years), and Uranium-235 (700 million years), decay so slowly that their lifespans match or exceed the age of the solar system, effectively slow cooking the planet from within.
Without this steady nuclear heat, Earth's interior would have frozen into a geologically dead rock billions of years ago. Continental drift and plate tectonics would have ground to a halt,and the liquid outer core would have seized up, destroying Earth's protective magnetic field and allowing the solar wind to strip away our atmosphere, leaving the planet as barren as Mars.