Assume it is the year one billion

[james_davis_nicoll]

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

Comments

[(Anonymous)]

To start: "Beware the beast Man, for he is the Devil's pawn. Alone among God's primates, he kills for sport or lust or greed. Yea, he will murder his brother to possess his brother's land. Let him not breed in great numbers, for he will make a desert of his home and yours. Shun him; drive him back into his jungle lair, for he is the harbinger of death."

[james_davis_nicoll]

I was thinking part of the vast, cool, and unsympathetic world-mind's programming was to also ensure humans are around, which it does by tweaking tetrapod lineages to produce bipeds with hands every few million years.

[jreynolds197]

"Alone among God's primates, he kills for sport or lust or greed."

ALICE: "That's like having a D&D campaign in which all orcs are evil, all dwarves are greedy, and all humans are willing to f*ck anything."

BOB: "Uh, that last one is kinda true."

ALICE: "Shut up," she explained.

[elusis]

"Alone among God's primates, he kills for sport or lust or greed" - not actually true, apparently.

https://www.bbc.com/news/science-environment-29237276

[(Anonymous)]

Presumably becoming sapient improved their character.

[roseembolism]

I blame that black obelisk.

[dsrtao]

Going to assume that's "one billion years from now".

The Sun should be about 10% brighter than it is now. It might be a good idea to put a nice big station out at the L1 Lagrangian point with adjustable sunshading. On those timescales, moving a nice big asteroid there is feasible. It's about 3-4x the distance to Luna.

A billion years is a substantial time for evolution. Multicellular life is only about half that old. There will probably be several die-offs and superspeciation events in that time period.

[kithrup]

Charlie covered this, in Palimpsest.

[dwight_benjamin_thieme]

How actively do you want to maintain your remediation? Putting a bunch of junk into Earth-equatorial orbit would help a lot, I would think. But the lighter the junk, the quicker it de-orbits, while stuff heavy enough to stay there for 1,000+ years might be too large to completely burn up on reentry.

[armiphlage]

If you're starting from the surface, perhaps it might be more energy-efficient to float reflective junk in the oceans? Better yet, self-replicating junk?

Diatoms have long-lasting transparent silica frustules, that sink to the bottom of the ocean when they die. What if you genetically engineered diatoms to grow opaque, pore-free frustules? Entrapped air would let them float, covering the ocean with a reflective scum. This would counteract increased solar flux, while also reducing evaporation of the oceans.

[armiphlage]

What if we sprayed reflective dust in the plane of the ecliptic between the Earth and Sun, stationary with respect to the sun, just inside the entire orbital path of the Earth? Light pressure would counteract the force of gravity. No worries about the upper atmosphere deorbiting it that way.

[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)]

UN-altered REPRODUCTION and DISSEMINATION of this IMPORTANT information is ENCOURAGED.

[mikeda]

A society wth really advanced tech might be able to somehow drop the sun’s brightness back down enough to keep the earth from overheating. Although any society capable of doing that eould probably also have the alternative (suggested above) of moving the Esrth to a more distant orbit.

[(Anonymous)]

Reducing the sun's mass would reduce the brightness (and extend the sun's main sequence lifetime). But I don't have a proposal to offer as to how that could be achieved.

[(Anonymous)]

Move it farther away from the sun. It'll take a while, but we have a while.

Riderius

[ariaflame]

At least moving it away is easier than moving it towards.

[dwight_benjamin_thieme]

Mount rockets on the Moon and you get to keep it (possibly?) when you go.

[ba_munronoe]

THUNDERING WORLDS!!!

(Sorry.)

[ba_munronoe]

Roof over the planet with nice shiny new tin roofs.

[voidampersand]

Planetary tinfoil hat protects from damaging radiation!

[(Anonymous)]

Would going underground be in any way feasible?

Drain the ocean to make a colossal refrigerant system, and put giant heat radiator fins to dump excess heat from the refrigerant. Could you have a colossal system of underground tunnels that are kept at a comfy 24C/75F (with cooler and warmer areas for those who like or need that sort of thing)?

[zxhrue]

a billion years?

that's a rilly rilly rilly long time

sol III is forgotten? purposely obscured as a luxury resort ala tetiaroa? obliterated in a long forgotten war? racoons?

or you know, planet in flight perhaps