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"Glassing" a planet is a common ultimate tactic in Science Fiction, basically it consists in using high power energy weapons to destroy all life on the planet and reducing the soil and rock of the surface of the world to several centimeters of a fused material, not dissimilar to this glass though generally it is described as being somewhat thicker than the deposits at Trinity.

Now this would appear to be a method one does not use if one wants to use the planet in question ever again but just how long would it take for a world to recover (recovery being measured as a return to widespread plant growth) from a glassing grade attack due to natural processes, without any technological intervention?

The answer to this question will vary greatly based upon the geology and climate of the world in question so assume an Earthlike world and assume that the oceans and atmosphere are, for all intents and purposes, completely intact. Life on the continents is destroyed and the ground fused to a depth of 3-4 centimetres and the edges of the ocean basins suffer some damage but otherwise ocean and purely atmosphere living organisms are intact.

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    $\begingroup$ Fun question. I suspect that the (now superheated) atmosphere and oceans would speed up recovery time, but that’s mostly a guess.. $\endgroup$ – Joe Bloggs Oct 8 '17 at 11:37
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    $\begingroup$ 3-4 centimeters seems rather shallow. I'd be able to survive in my basement if that's that case. $\endgroup$ – sphennings Oct 8 '17 at 11:51
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    $\begingroup$ @sphennings Not with a house over you you wouldn't, houses are not rocky substrate, neither are basements. $\endgroup$ – Ash Oct 8 '17 at 11:52
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    $\begingroup$ @sphennings You're right that a sufficiently hardened bunker might be used to survive the attack but I think you're badly under estimating the energy needed to create that glass layer. You're also right that it isn't that deep, this is deliberate. $\endgroup$ – Ash Oct 8 '17 at 11:55
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    $\begingroup$ @sphennings No it's not; in order for soil and rock to be fused in that manor requires temperatures at depth of 1470 Celsius, the hardiest construction in current usage is reinforced concrete which will largely evaporate at about 900-1000 degrees due to thermal decomposition anything else will be melted or burn at much lower temperatures. That's without taking into account thermal shock effects or the pressure/temperature effects on air in contact with materials at those temperatures. $\endgroup$ – Ash Oct 8 '17 at 12:46
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Let us take the process as per "face value", I've strong doubts it could really be performed as-specified (i.e.: very high ground temperature is bound to affect both atmosphere and cauterize to a much deeper depth), but that's another story.

Let us assume really just a few topsoil centimeters are heated instantaneously to something like 1500°C. This takes a huge amount of heat and would have several side effects:

  • Sudden increase of air pressure with consequent shock wave.
  • Melting of most superficial structures.
  • Collapse of "small" concrete/metal constructions.
  • Instantaneous fire of anything burnable.
  • Larger artificial structures (e.g.: concrete dams) would survive.
  • Relatively large underground installations would survive (e.g.: Carlsbad caves or Laboratori Nazionali del Gran Sasso).
  • A huge amount of oceanic water would evaporate from heated surface.

Note: I see no way to confine effects to a few centimeters of ground while destroying all military underground facilities, but that's (again) beyond the point).

Effects in the mean/long period are:

  • Huge amounts of dust/smoke/particles would be released in the atmosphere.
  • Huge amounts of CO2 would be released in the atmosphere.
  • Water evaporated would produce heavy rains.
  • Cool-down, especially in zones where there's little to burn, would be fast (hours/days).
  • Glass cover would crack, due to contraction, in relatively small pieces because thickness isn't enough to give structural strength.
  • "Nuclear winter" would settle for (at least) a few years.
  • Any seed not cooked by heat would start to germinate through cracks.
  • There would be a huge mass-extinction, but many amphibious species (real amphibians, but also tortoises, seals and similar animals, as long with birds "lucky enough" to be in flight) would survive, some to die of hunger because of missing food (e.g.: seed eating birds).
  • There would be a rapid decrease of Oxygen content in atmosphere due to globalized fires.
  • At the end of "Nuclear Winter" flora would thrive in the CO2-rich environment; in the first period the "glassy ground" would hamper it a bit, but a few centimeters are not enough to hold for long.
  • It is unsure what would happen to climate; most likely there would be an initial extension of deserts (all the planet would be a desert, in the beginning, but that wouldn't last a year) because many areas have high rain because of the forests they host (not vice versa).
  • Cooler climate and high CO2 do not mix, so a complete meltdown of icecaps is likely, with Antarctic back to rainforest (if seeds can reach it).

I would guess most of planet would have at least some "widespread plant growth" in relatively short period (<100years).

Terrestrial animal life would fare much worse and evolution will have to start again with a huge setback. It is possible there would be a "jump-start" fed by pinnipeds instead of fishes. Anyhow to have real terrestrial animals (without intervention) would take million years (unless some animal managed to escape destruction).

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  • $\begingroup$ You really think a wet concrete structure would survive that kind of heating event? I realise the kill depth will be pretty severe, I imagine it would probably sterilise a metre or so of depth to fuse the top few centimetres of material on the other hand soil and rock are pretty good insulators. $\endgroup$ – Ash Oct 8 '17 at 14:59
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    $\begingroup$ "wet" is not the point. If you want to confine the vitrification to a few centimeters the amount of heat needs to remain pretty confined. Any big structure would suffer only in the external strata, so a dam would lose a few centimeters of superficial concrete, a small percentage of its many meters thickness (for reference: Hover Dam base is 200m thick and its rim is "only" 14m thick). Real effects would heavily depend on how and for how long you deliver heating. As said I see no way to produce an effect as you describe. $\endgroup$ – ZioByte Oct 8 '17 at 15:39
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    $\begingroup$ Sorry question didn't quite say what I thought it did, kill everything, fuse the ground to 3-4 centimeters down. Not just kill everything to 3-4 centimeters depth, I doubt you'd have to fuse much of anything to sterile the top few centimeters of the ground. Trinity fused a maximum of 2 centimetres with 4.3x10^12 Joules of heat, on that basis I thought 4 centimetres was going to be too much. $\endgroup$ – Ash Oct 8 '17 at 16:09
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    $\begingroup$ I didn't manage to make my point (sorry, English is not my mother tongue). What I wanted to say is there's no way you can vitrify with something like a bomb without affecting (a lot!) the atmosphere above ground. If you want to preserve aeroplancton you need to (somehow) concentrate energy release at ground level; in this case total amount of energy is much less and, probably, not enough to severely damage big structures (and probably leaving underground facilities intact). Any other mean would have deeper (in all meanings!) impact than you seem to imply. $\endgroup$ – ZioByte Oct 8 '17 at 17:00
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    $\begingroup$ @AnoE: sorry, I fail to understand your comment. in the actual Answer I expressed a passing doubt and then I proceeded to answer exactly the question ("... most of planet would have at least some "widespread plant growth" in relatively short period (<100years)"). OTOH Comments focus on actual feasibility of "starting conditions". $\endgroup$ – ZioByte Oct 9 '17 at 6:30
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We could take a real-life (well, real-death) approach here and focus on the most dramatic biological catastrophe on Earth, called the end-Permian crisis. At this point an abundance of life forms existed, which was nearly wiped out around 250 million years ago (250 Ma), with only 10 per cent of plants and animals surviving.

The end-Permian crisis is believed to have been triggered by a number of physical environmental causes, including global warming, acid rain, ocean acidification and ocean anoxia. Vulcanic eruptions may have accompanied it, or perhaps a meteor impact.

It is currently much debated how life recovered from this cataclysm, and whether quickly or slowly. However, it is is generally thought that living, breathing organisms didn't truly recover until 10 million years later (source: Live Science).

You specifically ask about recovery of plant life - Grauvogel-Stamma & Ash (2015) report that the Triassic floras began with the proliferation of the lycopsid Pleuromeia (an extinct genus of spore plants) during the Early Triassic (250 to 247.2 Ma) and that it proceeded with the resurgence of the coniferae (conifers) in the early Middle Triassic (Early Anisian: around 247.2 Ma), the return of the cycadophytes (a genus of ancient seed plants still around today) and the pteridosperms (several groups of extinct 'seed-ferns') in the Late Anisian (around 242 Ma).

Reference
- Grauvogel-Stamma & Ash, Comptes Rendus Palevol (2015); 4(6–7): 593-608

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    $\begingroup$ That is one hell of a citation. I learnt some words from the abstract I didn’t even know were things! $\endgroup$ – Joe Bloggs Oct 9 '17 at 5:52
  • $\begingroup$ That's a nice answer! Imho, it would benefit from some fleshing out, though. $\endgroup$ – Burki Oct 9 '17 at 6:53
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    $\begingroup$ @AliceD: it’s not strictly necessary, but more resilience to dead links is no bad thing. $\endgroup$ – Joe Bloggs Oct 9 '17 at 8:52
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    $\begingroup$ global warming, acid raid, ocean acidification and ocean anoxia....sounds like what manmade climate change is doing.... $\endgroup$ – Marshall Tigerus Oct 9 '17 at 15:29
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    $\begingroup$ @MarshallTigerus Glassing a planet is the ultimate in climate change. $\endgroup$ – a4android Oct 10 '17 at 4:13
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The amount of energy required to fuse the soil of the planet to glass in a matter of seconds is comparable to the energy release of a nuclear weapon (after all, the nuclear glass in the Trinity site was created by a nuclear weapon).

When extrapolated over a planet, this would probably remove the atmosphere and a large portion of the oceans as well. Just based on those observations, the proper answer is going to be "never".

You can work this problem in the other direction; if your civilization were to find an airless planet with an unweathered rock surface and no atmosphere (think of the Moon), what steps would they need to terraform it? Resupplying an atmosphere, covering the surface with liquid water and providing enough energy to "till" the surface in order to make a sand substrate for soil building will all be needed to start the process.

If you take these steps (similar to some of the proposed ideas to terraform Mars), and then simply rely on biological processes, you would probably have to wait several thousand years for mosses, lichen and so on to build the soil and for plants to take root and spread.

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    $\begingroup$ I don't understand how superheating would remove the atmosphere? The gravity that holds the atmsphere is still present, the same goes for the magnetosphere, and the fire from the heat will create a lot of gas (CO2 and many more). While some of the atmosphere might be blasted away, i don't think a complete loss of atmosphere is plausible. $\endgroup$ – Burki Oct 9 '17 at 6:50
  • $\begingroup$ @Burki: the basic idea is that extra energy increases the chance any one particle will be bumped upwards at escape velocity by any other particle, but you’re quite right: this won’t remove the whole atmosphere. At worst it will speed up the rate some lighter gases are lost. Certainly not worth worrying about unless you can keep the planet superheated for a long time. $\endgroup$ – Joe Bloggs Oct 9 '17 at 11:26

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