Assume it is the year one billion

[james_davis_nicoll]

How can one maintain the Earth's ability to support complex life?

Comments

[graydon]

If you're supposing planning on this time scale, you gravity tractor the earth into a more distant orbit rather than messing about with sunshades.

[(Anonymous)]

Can't do that. President's wife's astrologer says that'll fuck up his charts.

[graydon]

More than the billion years?

[(Anonymous)]

As long as Thuban is still the pole star, everything's OK.

William Hyde

[jsburbidge]

At that time scale you could allow for more room by building some more planet-sized bodies and adding them to the more-distant earth orbit in a Klemperer rosette

[graydon]

How long does it take an accreted planet-sized body to cool? It seems awfully long term, even for this project. The Culture take -- orbitals are easier, faster, and more portable than planets -- might well apply.

[(Anonymous)]

If the life has to be carbon-based waterbags then yes, the hotter sun evaporating all the water is a problem. But are we allowed to go to nanotechnology? Then losing the water might be better, avoids rust. We might drop the oxygen as well. When I say "we"...

From the personal computer of

Robert Carnegie

[graydon]

Adding water is not that hard; lots of water in the outer system.

It's getting more uranium into the core to keep plate tectonics going that seems rather intractable, at least if you want to continuously maintain the habitability of Earth's surface.

[jbwoodford]

AIUI radioactive decay isn't the major driver of plate tectonics; most of the heat in the core is primordial, but the cooling mechanism is very different from what Kelvin assumed.

[graydon]

Might just be the magnetic field, then.

Also, "adding heat to the core" does not immediately seem easier than adding uranium.

[ba_munronoe]

Do we have a reliable estimate on how long it will take to cool down enough for plate tectonics to stop? A billion years is only increasing the age of the planet by 22%: do we have indications that plate tectonics have become much less active in the last billion?

(I'd bet money on this being a problem if we're trying to go for the full five billion years till the sun becomes a red giant, but one billion? The magic 8-ball says answer unclear, ask again later).

[graydon]

Seem to recall some discussion that plate tectonics are already slowing down significantly; the error bars from trying to graph eroded orogeny volumes and what that does to atmospheric chemistry aren't small, though. The implications for life involve mineral recycling; how much bio-available calcium, potassium, iron, etc. is there? (there's the continued controversy over what the particulate plumes from East Asian industrialization have done to Antarctic marine production; it can be really small absolute amounts controlling biosphere productivity.)

The other thing is that we're getting increasing consensus that Venus went from wet with an active surface to its present state in less than a billion years, but just what or how remains an entirely open question. So the time frame is plausible for "plate tectonics stops".

[ba_munronoe]

Well, thank you for expanding my ignorance. :)

Any suggestions for reading re what's new in plate tectonics?

[graydon]

Alas, no; the above is random clicking leading to trying to find the actual article. NOT a field where I can claim it would even nod back to acknowledge the acquaintance.

[roseembolism]

I would say that's simply a matter for a Sufficient Large and Powerful enough laser.

Any environmental remediation issues are the problem for a different department.

[izeinwinter]

Make a singularity small enough to decay in 3/4ths the time it would take it to fall through the earth. Drop it. Repeat as required

[(Anonymous)]

The canonical papers on radioactives not being the main source of mantle heat:

  http://cires1.colorado.edu/science/groups/molnar/pubs/2007GSAT.England.PerryKelvinBlownOpportunity.pdf
  https://physics.ucf.edu/~britt/Geophysics/Readings/R6England.pdf

There's also this review of the geology of the mantle:

  https://people.earth.yale.edu/sites/default/files/files/Karato/23_190%20Karato%20(2010%20GR).pdf

On page 23 of the PDF, there's Fig 17, which depicts how the specific regime of viscosity contrast of the mantle and the near surface layer allow for plate tectonics, which will otherwise not occur. I confess that the paper is way over my head, so if any geophysicists can explain that section, I would appreciate it.

I don't understand the reasoning behind the claim that plate tectonics is necessary for habitability. What happens to the surface that reduces/ends habitability if plate tectonics stops?

[(Anonymous)]

I believe that the notion is: things naturally sink to the deep basins of the oceans, & there are large areas of them. Once there, they are unavailable to almost all life, especially surface life. But with plate tectonics, the basin gets subducted & melted, and all the sunken goodness can be released like Godzilla & Cthulhu, but in this case via volcanoes. The carbon dioxide can keep plants going. Minerals are spit into lava and become bioavailable too after erosion. Or if the ocean basin rises instead, it's more directly available. - Tim

[armiphlage]

Paging Alexander Abian ...

[(Anonymous)]

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