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In this world, a planet with very dense vegetation (earth-tropical-forest-like) and silica containing soil was attacked by spaceships which fired very high energy laser beams across the planet's entire surface, effectively vitrifying it.

  • this planet's outer crust was only soil not solid rock or water, life developed thanks to underground water pockets (10 to 50 meters deep)
  • the first 8 to 15 meters of soil (depending on location) were fused into glass
  • all vegetation in this depth range was immediately incinerated
  • some of the plants used to reach down to 20 or 30 meters underground, and a lot of very resilient seeds were disseminated at these levels as well as volatile seeds in the atmosphere
  • all of those plants need sunlight and oxygen to develop, but seeds can stay in cryptobiotic-like stasis for as long as thousands of years

question: Could vegetation plausibly break the surface and grow again, after 1300 years time?

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    $\begingroup$ There's also the possibility that things will grow on the surface of the glass. $\endgroup$ – Daniel Bensen Nov 2 '17 at 7:30
  • $\begingroup$ soybean!!! BTW Welcome ;D $\endgroup$ – user6760 Nov 2 '17 at 7:39
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    $\begingroup$ Welcome to WorldBuilding Unlambder! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Sec SE - clear Monica's name Nov 2 '17 at 8:03
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    $\begingroup$ Note that the atmosphere will be changed by such an event. Lots of combustion byproducts, like CO2 if it was similar to today's Earth, and the massive temperature increase may or may not cause it to partially evaporate to space. Massive quantities of water vapour (or local equivalent) may also have been produced, though much of it should fall back once temperatures drop again. But assuming the surviving plants are a hard, adapting bunch, some of them at least should thrive in the new atmosphere and climate (assuming it didn't go full Snowball or Venus). $\endgroup$ – Eth Nov 2 '17 at 12:09
  • $\begingroup$ Arch-soybeans are part of the plan :D @user6760 $\endgroup$ – user44285 Nov 3 '17 at 11:45
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It's highly likely vitrified surface will start cracking in a very short time due to thermal contraction initially, then thermal cycles and, in the long term, tectonic activity.

Vegetation is likely to spread from there, given characteristics you state (seed resilience and root depth, mainly).

Depending on specifics of soil and irradiation process you can have either large placques with deep canyons (more likely on rocky ground, but possible elsewhere, particularly where vitrification is deeper) or finer fragmentation in (relatively) smaller boulders.

In the former case vitrified soil would be very evident even after millennia, while in the latter I suspect vitrified rubble to be completely colonized in matter of few centuries.

Other things to note:

  • this vitrified soil isn't "lava like" because it's composition isn't mainly silicates, but it's much more varied.
  • "Vitrification" is likely to be covered by a lighter stratus of lighter material, possibly rocky foam containing high quantities of high nutritive substance coming from ecosphere destruction.
  • liquid "glass" is likely to be a very fluid lava-like thing, at least at beginning, unlike "true glass", so it's likely to flow filling valley's leaving mountain tops (almost) bare.
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    $\begingroup$ And existing plant matter was incinerated, not vapourised. The ashes will remain as impurities within the glass and act as faults causing the glass to break that much faster $\endgroup$ – nzaman Nov 2 '17 at 14:14
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    $\begingroup$ @nzaman: Exactly my thoughts. Also add that superficial "glass foam" will contain most of the impurities and thus act as fertilizer for plants managing to break to surface trough cracks. This should reduce considerably regrowth time. Depending on specifics of laser vitrification a huge amount of cinder may be released in the atmosphere and contribute to humus reconstruction. $\endgroup$ – ZioByte Nov 2 '17 at 19:22
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We already have examples of glassy ground on Earth: volcanic eruptions can give as an outcome obsidian ground, which is basically basaltic glass.

Weathering and erosion makes it possible for vegetation to grow back on this soil after a few years, following a well established sequence: first pioneer plants, followed by more diverse flora.

After 1300 years is very likely you will have to dig deep to find traces of the vitrified soil (look at Pompei).

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I think you could work it out in three ways:

  • The water pockets you described, due to the extreme heat, "bubbled" outside throught the melted glass, alongside the dormant seeds, and created craters around which vegetation can easily grow because of deeper soil emerging alongside water.
  • Such a violent event is unlikely to result in a smooth and perfectly integer glass surface: there will be cracks in it, cracks that can be widened by regrowing plants.

  • You can suppose that the ashes of the previously existing plants gathered in valleys and lower grounds, creading an highly alkaline soil, allowing only specific flora to install on it.

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  • $\begingroup$ And airborne seeds will be among the ashes too. $\endgroup$ – Tonny Nov 2 '17 at 14:25
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If you ignore the fact (or at least the highly likely possibility) that heat which is sufficient to vitrify 15 meters of soil -- bummer is that hot -- will destroy all life in a depth 30 meters as well (it might not incinerate everything, but that's not necessary, some 50-60°C over a period of several hours or days are entirely sufficient to kill everything except thermophile bacteria)... then yes.

Even without the assumption that the glass will crack naturally (or will be cracked by the expanding heated water), this is quite possible. Nature is a tough and unforgiving bastard with eternal patience.

You can reword your question into one that can be immediately answered: "Could vegetation plausibly dig through 70 meters of massive rock?". The answer to that is: Yes of course, that's what you can observe in the underground caves below St. Emillion. The city as well as its vineyards is located on top of one huge, huge rock. There exist man-made (well, man-extended) caves below that rock. And sure enough... roots from the above wineyards come through the ceiling. It takes a vine a mere 80-100 years to achieve that, so 1,200 years for something half the distance should be plenty.

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