The Planet Inside: Scientists are probing the secrets of the inner core | Hacker News Reader

The Planet Inside: Scientists are probing the secrets of the inner core

science.org

40 pointsHooke5 comments

This got me thinking about the earth's heat flux to the surface. It comes from primordial heat and radioisotope decay of thorium and uranium. Wild that geothermal energy is really just nuclear decay energy, just like the mars RTGs. But disappointing that it ain't all that much at just 47 TW, compared to the sun's 200,000 TW on the Earth's surface. And of those 47 TW, only 14 TW are on land. Not even close to enough to power mankind and our 20-40TW of primary energy today, and hopefully much much more in the future.

Be sure to scroll the article down to the responses, for an excellent comment of an actual seismologist who appears to be mildly irritated by the usual scientific news cycle.

That's more of a "you didn't mention my recent research on this" than frustration with the "usual scientific news cycle".

(The commenter does have a good point, though -- the writeup is on "Hey, these observations conflict. That's weird!", and the commenter is saying: "Hey, we published a paper on that conflict several years back that we think explains it well, you missed that hypothesis when going over papers that discuss that conflict". It's kinda their pet theory, and pretty wild, but it was still a Science paper/very prestigious/respected.)

This is actually a _really_ excellent general audience summary. It's hard to beat Science's non-technical sections like this for scientific reporting.

For a little more context on the "pet theory" part, Wen (2006) (The commenter) looks at waves that reflected off the same spot at the surface of the inner core 10 years apart and proposes that the differences in reflections are because the core itself grew by ~1km in 10 years at that location. You can also explain these differences by spin (the boundary is moving) or a few other mechanisms, but you can't rule out "the radial location of the boundary changed".

That's basically the point - spin can explain it, but we've measured inconsistent spins. The inner core boundary moving around vertically by a few km can explain it, but that is a little hard to stomach for geologic reasons.

The issue is that it's _really_ hard to come up with a geologically plausible mechanism that would allow 1km of vertical solidification over a significant area in only 10 years that's also compatible with the liquid outer core existing at all. The paper proposes that it's constantly growing and eroding so the net gain/loss is essentially 0, but again, how do you explain that rate of 1km of solidification in 10 years geologically?

That's what moves it into the "pet theory" camp. It's not crazy, but no one's been able to come up with a convincing mechanism for the proposed very rapid growth+erosion of the inner/outer core boundary and there are other explanations (like spin of the inner core relative to the rest of the Earth) that have gained broader acceptance. The comment of "Hey, we have an alternate explanation for this that wasn't mentioned" is also pretty fair, though.

The part about the dynamo being 10x lower 500 m.y.a. compared to today suggests that the background radiation was 10x higher. They point out that lower dynamo leads to more atmospheric loss to space, thus limiting biological activity. Butthe the great reduction in radiation could be similarly impactful, allowing for more manageable genetic mutation.

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