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Comment by rdtsc | Hacker News Reader

> For a time, the mantle would get hotter, since the shell around it would trap heat generated by radioactively decaying compounds inside it. As heat accumulates in the interior, the Earth in Kane’s simulations would experience an uptick in volcanism lasting for about 15 million years.

That totally surprised to me. I had no idea radioactive decay played such a role for earth. It turns out I must have fallen sleep in one of the classes when that was explained.

https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget

> The radioactive decay of elements in the Earth's mantle and crust results in production of daughter isotopes and release of geoneutrinos and heat energy, or radiogenic heat. About 50% of the Earth's internal heat originates from radioactive decay

View on HN

Dually: geothermal energy installations (& volcanism) release much more than simply energy into the biosphere

https://www.ntanet.net/hot-rocks-radioactive-waste-radon-fro...

You are welcome to consider that as a matter of hormesis and resources, of course

The only context in which I heard it mentioned is the idea of trying to date the earth by its temperature. Assume it was a hot molten mess in the past and has been cooling down ever since. Factor in the rate at which it would radiate heat and all of the energy coming from the sun and... you conclude that the planet is very young. Because you didn't account for radioactive material within the planet, keeping it warm.

Thermal decay dating was also used to estimate the age of the Sun, most famously / notoriously by William Thompson, a/k/a Lord Kelvin. Without knowledge of radioactivity, nuclear chemistry, or nuclear fusion, Thompson presumed latent heat of gravitational collapse for both the Earth and Sun, and came up with an age of "a moderate number of millions of years" for the former, and no more than 500 million years for the Sun.

Rutherford's discovery of the atomic nucleus, and subsequent discoveries of radioactive decay (providing both mechanism and clock for Earth's heat and age) and fusion and helium (the Sun's thermodynamic equation and age) provided a refutation of Thompson's estimates, empirical basis for the current age estimates of the Earth and Sun (about 4.5 billion years), and ultimately of a lifespan for the Sun (about 10--12 billion years) as well as how long habitable conditions on Earth may persist (as little as another 800 million years for some conditions, another 2--3 billion on the outside).

<https://www.teachastronomy.com/textbook/Our-Sun-The-Nearest-...>

<https://en.wikipedia.org/wiki/Lord_Kelvin#Age_of_Earth> citing Burchfield, Joe D. (1990). Lord Kelvin and the Age of the Earth. University of Chicago Press. p. 43. ISBN 978-0-226-08043-7. <https://en.wikipedia.org/wiki/Special:BookSources/978-0-226-...>

> It turns out I must have fallen sleep in one of the classes when that was explained.

Unless you've studied this at a post-secondary level, I'm afraid that it's quite likely that you've never had it explained to you. My highschool discussed at length the role that the sun, the greenhouse effect, oceans, forests, agriculture, mountain ranges, etc, play on weather and climate, but never actually went through the exercise of energy accounting to determine what keeps the Earth warm.

Which is understandable, because that exercise is non-trivial, and will not actually be convincing to anyone who doesn't have a calculus education.

Proving the equilibrium requires calculus but simply writing it down doesn't? It's not different from these "water flows into and out of the pool" exercises.

Radiogenic heating as a primary factor in Earth's heat budget and geologic processes might very well not have even been firmly established when the OP was in school. Alot of what is now confidently taught about Earth's geology and geological history is surprisingly recent compared to other scientific fields. Plate tectonics wasn't firmly established until the 1960s. The Chicxulub impact was highly contentious until the 1990s and not conclusively proven until the 2000s, and AFAIU even today there's still some debate about its role in the Cretaceous extinction, e.g. the interaction with other concurrent events. I wouldn't be surprised if the importance of radiogenic heating wasn't canonical until 1980s, 1990s, or even later and therefore not mentioned in a standard curriculum until Millennials reached high school. I don't remember it being mentioned at all in the 1990s, though re other facts my high school geology and biology textbooks were often many years out of date in some areas--an important and useful coming of age lesson for me, that even academic text books can be and often are sorely antiquated and even outright wrong; and a lesson I might not have learned so early if I hadn't had the advantage of the early Internet.

While radioactive decay plays a significant role in the internal temperature of the Earth, the internal temperature of the Earth plays only a tiny role in the temperature of the surface and atmosphere of the Earth—about 0.03% of the climate energy budget. So for high school geoscience, it’s not worth more than a mention.

If i remember right, according to one of Asimov's Foundation sequels, the Earth was unique due to its high level natural radioactivity, which allowed it to develop an ecosystem more vibrant than any other planet in the galaxy.

Was just rereading - it was the radioactivity and the large natural satellite that was unique in his universe. Tides are interesting because once you have life in the oceans, it's a kind of forcing function to adapt to land conditions

Forcing function + making a stretch of land which is neither dry nor enterily wet. A gradient. If there are no tides the leap life has to make is much bigger.

Fascinating

And perhaps the advantages of this gradient extend up as far as aquatic apes.

Not sure what this means.

I assume they are referencing the long-debunked theory that man evolved from a line of apes that became semi-aquatic for a while.

Yup that's where I was aiming. Is it thoroughly debunked ? It's a cool idea.

Why are tides a forcing function? Marine life has been perfectly content just not going near a beach.

> Why are tides a forcing function?

"Nucleotide formation and polymerization are both more favored thermodynamically when subunit and nucleotide concentrations increase and the water concentration decreases (i.e., at low water activity)" [1].

Tide pools provide a regularly-cycling low-water and high-water environment. (And you get thermocycling, nutrient refreshment, and a path to the oceans, too.)

They're not a forcing function, generally, because we don't know how life formed. But I believe they're close to one in a RNA-first or metabolism-first origin-of-life universe.

[1] https://www.nature.com/articles/s41467-018-07389-2

Very interesting, thank you!

I was thinking more on the lines of "if marine life never found itself stranded on land, it wouldn't need to evolve to survive on the land"

Wasn't Asimov a science fiction writer?

He was a popular writer of both fiction and nonfiction, had a PhD in chemistry, and wrote on numerous topics, including science, history, Shakespeare, and the Bible.

He and Arthur C. Clarke had a (tongue-in-cheek) agreement:

The feelings of friendship and respect between Asimov and Arthur C. Clarke were demonstrated by the so-called "Clarke–Asimov Treaty of Park Avenue", negotiated as they shared a cab in New York. This stated that Asimov was required to insist that Clarke was the best science fiction writer in the world (reserving second-best for himself), while Clarke was required to insist that Asimov was the best science writer in the world (reserving second-best for himself). Thus, the dedication in Clarke's book Report on Planet Three (1972) reads: "In accordance with the terms of the Clarke–Asimov treaty, the second-best science writer dedicates this book to the second-best science-fiction writer."

<https://en.wikipedia.org/wiki/Isaac_Asimov#Other_authors>

He was both a science and science fiction writer. Check out "View From a Height" for example. An excellent book.

https://en.wikipedia.org/wiki/View_from_a_Height

He wrote a book about jokes and how to tell them. Quite good.

There was a mention of something like that in Starship Troopers as well.

Heinlein describes life on an earth-like planet with low radiation as being "like a kid who takes ten years to learn to wave bye-bye and never does manage to master patty-cake".

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