So we glassed it, now what?

Question

"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.

Answer 1

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).

Answer 2

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).

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

Answer 3

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.