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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.

Ash
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    Fun question. I suspect that the (now superheated) atmosphere and oceans would speed up recovery time, but that’s mostly a guess.. – Joe Bloggs Oct 08 '17 at 11:37
  • @JoeBloggs Hmm I hadn't thought of that. – Ash Oct 08 '17 at 11:38
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    3-4 centimeters seems rather shallow. I'd be able to survive in my basement if that's that case. – sphennings Oct 08 '17 at 11:51
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    @sphennings Not with a house over you you wouldn't, houses are not rocky substrate, neither are basements. – Ash Oct 08 '17 at 11:52
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    @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. – Ash Oct 08 '17 at 11:55
  • @Ash there is more than 3-4 centimeters of buildings material above me. Per your definition 3-4 centimeters of dirt and rock would be enough to protect me. Structurally my building is sturdier than that. – sphennings Oct 08 '17 at 12:16
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    @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. – Ash Oct 08 '17 at 12:46
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    What kind of glassing is this? If you glass a cornfield, do you burn it to the bedrock? Or just until there's enough molten silica to form a crust? If it's instant you will get a steam explosion and a plume of molten glass not unlike a volcanic eruption, but not necessarily a glassy crust. There's a world of difference between 'high powered laser until it's shiny' and 'instant heat burst' in terms of what happens to the soil. – Resonating Oct 08 '17 at 16:59
  • @Resonating Given the final effect has been described your question as stated has been answered yes? What else needs to be stated from your point of view? – Ash Oct 08 '17 at 17:09
  • Recovery time is also likely to be dependent on whether the planet is just getting a heat treatment (a melted, but inert shell) or a radiation-based one (a melted and radioactive shell). – Dave Sherohman Oct 09 '17 at 07:42
  • Some ideas on another answer https://worldbuilding.stackexchange.com/questions/54681/how-much-heat-energy-would-be-needed-to-turn-a-large-section-of-desert-sand-into – KalleMP Oct 09 '17 at 16:13

3 Answers3

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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).

ZioByte
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  • 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. – Ash Oct 08 '17 at 14:59
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    "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. – ZioByte Oct 08 '17 at 15:39
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    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. – Ash Oct 08 '17 at 16:09
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    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. – ZioByte Oct 08 '17 at 17:00
  • Right so it's more up that's a problem than down is that what your saying? I.e. the atmospheric, and possibly oceanic, effects are going to have to be much greater to do that much surface melting with known technology, the starting scenario will be far more sterile than I have posited then? The energy figure is the estimate for the ground absorbed heat to create 2 centimetres of Trinitite. – Ash Oct 08 '17 at 17:10
  • Note that nuclear winter on this scale is likely to do a number on marine flora, which will cause big problems for recovery. However, since Snowball Earth apparently did recover, the long-term effect should be workable. Where "long-term" indicates 600 million years, or so. – WhatRoughBeast Oct 08 '17 at 17:23
  • You need to decide (more or less, of course) what means you want to use to deliver required heat. The "normal" means (i.e.: a set of about one H-bomb/km2) would thoroughly sterilize the planet, not to speak about fallout. Other means (e.g.: a gigantic lens in L1 concentrating Sun light on a single meridian line while Earth rotates under it) would leave most of underground facilities untouched. Anything like Death Star would leave a planet as a scorched molten ball with little atmosphere and no water. "Glassing" is not for half-measures ;) – ZioByte Oct 08 '17 at 17:24
  • @WhatRoughBeast: I assume nuclear winter would rebound quite violently in a very short time (few years), given the amount of CO2 a global fire would release in the atmosphere. – ZioByte Oct 08 '17 at 17:27
  • @ZioByte Nuclear winter calculations generally hang on the particulate count, how much ash and dust go up and how fast do they settle afterward, the main factor in settling that material out is probably water vapour. – Ash Oct 08 '17 at 17:38
  • @ZioByte - Yes, but the question is, how long can aquatic flora survive without light? Days? Weeks? Years? – WhatRoughBeast Oct 08 '17 at 20:43
  • @WhatRoughBeast: that's "nuclear winter", not "nuclear night"! It is supposed to reflect back enough sunlight to lower noticeably temperatures for a few years at most. Light is still coming through and you wouldn't notice the difference. Many plants would be hampered and some wouldn't sprout at all for the whole period, but seeds are known to resist many years waiting for the right conditions. Aquatic flora would fare much better as water temperature would not swing wildly and they would get light enough. Everything depends on what really is the trigger cause. – ZioByte Oct 08 '17 at 21:32
  • While this answer is very inventive, it focuses on everything but the actual question. The OP stated that aquatic and air life is not perturbed, and made it pretty clear that it's not about how the process works. Poof, the planet is glassy and all surface life is gone. How would evolution start out from there? – AnoE Oct 09 '17 at 05:39
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    @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". – ZioByte Oct 09 '17 at 06:30
  • @AnoE It isn't as simple as just "poof" though, because the side-effects of the "glassing" process (most notably evaporated water, dust, CO2 and nuclear winter) will affect how the planet recovers. – Graham Oct 09 '17 at 14:08
  • @ZioByte CO2 would probably have little effect to a rebound after a nuclear winter of that scale. Its impact would probably be negligible compared to the far more powerful water vapour as a greenhouse gas, but even then it would probably not be enough to counter a runaway snowball Earth: after years of light reflected by the clouds, everything is frozen and covered in ice. At this point, most of the energy from the Sun is reflected back, even after the clouds are gone. It seems that only extremely long-lasting and massive volcanism broke Earth free from it. – Eth Oct 09 '17 at 16:14
  • @Graham, the point is that he specified what he is asking about in his question, and specifically said that he is not concerned about side effects. It's like a question "if a human could fly, what would happen in situation XYZ" and someone answers "humans can't fly." And ZioByte, you are right, some way down you start answering the question. Sorry. I somehow got lost in the first 20 sentences (at my screen resolution). ;) – AnoE Oct 09 '17 at 19:51
  • @AnoE: The first sentences are there to set the framework for the answer. I'm unable to give a meaningful answer without stating some "boundary conditions" that deeply influence the answer itself. If OP doesn't think what I wrote in the first part is relevant for his world then all remaining bears little relevance also. – ZioByte Oct 09 '17 at 20:04
  • @AnoE Where you you think you read that? I can't see anything in the question or any earlier edit which even slightly suggests what you say. He simply asks what would happen, and the answers will vary depending on how you got there. From your "if humans could fly" analogy, it is not saying "humans can't fly", it is saying "if humans have wings then this happens, but if humans have the power to manipulate gravity then this happens instead". This is 100% valid, and failing to mention it would be failing to answer the question properly. – Graham Oct 10 '17 at 11:42
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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

AliceD
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    That is one hell of a citation. I learnt some words from the abstract I didn’t even know were things! – Joe Bloggs Oct 09 '17 at 05:52
  • That's a nice answer! Imho, it would benefit from some fleshing out, though. – Burki Oct 09 '17 at 06:53
  • @JoeBloggs, thanks! Do you guys care about a reference list, as URLs may disappear over time? The current link is likely going to stay up, but a more formal citation will exist indefinitely. Barred any cataclysmic events that is ;-> – AliceD Oct 09 '17 at 07:39
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    @AliceD: it’s not strictly necessary, but more resilience to dead links is no bad thing. – Joe Bloggs Oct 09 '17 at 08:52
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    global warming, acid raid, ocean acidification and ocean anoxia....sounds like what manmade climate change is doing.... – Marshall Tigerus Oct 09 '17 at 15:29
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    @MarshallTigerus Glassing a planet is the ultimate in climate change. – a4android Oct 10 '17 at 04:13
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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.

Thucydides
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    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. – Burki Oct 09 '17 at 06:50
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    @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. – Joe Bloggs Oct 09 '17 at 11:26