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I have in my world a "crystalline desert". The idea is that a major cataclysmic event turned the surrounding area into glass, color irrelevant. Then following the event, major earthquakes and the passage of time broke it up into much smaller pieces, at least on the surface. There could be major chunks of "glass" below the surface I suppose.

The end result is a desert made predominantly of little tiny glass shards (I suppose they would turn into beads over time).

edit: I will add that when I say glass I mean a solid shiny surface, so glass like in appearance, it doesn't have to be chemically identical to glass

edit2: Occurred to me I should mention that the area in question is quite large. Say the size of Texas but circular. 268,581 sq/miles. It can be 'more' glassy in the middle and only partially towards the edges.

edit3: I want to clarify that I do not require an event. The event will be magical in nature, but that doesn't mean that a hellish firestorm couldn't cause problem globally.

  • What kind of temperatures would have to be achieved to do this to a temperate area?
  • Would the event have to take place in an area that was a desert in the first place? Is sand required?
  • What would be the global impact of such temperatures in a localized area?
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  • $\begingroup$ you want to know what cataclysm could have caused this ? $\endgroup$ – Vincent Nov 7 '14 at 16:39
  • $\begingroup$ Not specifically, I can create an event to match, my world has magic. $\endgroup$ – James Nov 7 '14 at 16:50
  • $\begingroup$ There was a Dungeons and Dragons world that had an obsidian sea. Obsidian is a bit harder to justify over glass from sand...interested in an attempted obsidian sea answer? $\endgroup$ – Twelfth Nov 7 '14 at 17:28
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    $\begingroup$ U should notice that glass is notoriously amorphous rather than crystalline. $\endgroup$ – Anixx Nov 8 '14 at 18:22
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    $\begingroup$ I'd like to propose 'Create Glass lake' as a high level magical spell in your world :) $\endgroup$ – Twelfth Nov 10 '14 at 18:30
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As a materials engineer the concept of a crystalline desert full of glass is baffling, as the two terms, crystal and glass, mean essentially opposite things. I'd like to start by making sure we are using the same terminology. I apologize in advance if I come across as lecturing! It is not my intent to bring bad feelings.

Some Terminology:

A crystal is most commonly defined as a periodic lattice with a repeating unit cell. A crystalline material would thus have its atoms arranged periodically on a regular grid in space and thus exhibit long-range order. If you were to move around the crystalline material, you would see the same atoms whenever you move one unit of distance along one of the axes of the lattice. Crystals are highly organized, and in thermodynamic equilibrium are the preferred state of all inorganic matter when in the solid phase.

An amorphous material is a condensed material that does not exhibit long-range order, and both liquids and solids can be amorphous. When a solid material is amorphous, it is commonly called a glassy material, glassy solid, or simply a glass.

Well, why does this matter?

Cooling rates! Allow me to explain:

I did mention that in thermodynamic equilibrium crystals are preferred for inorganic matter in the solid phase. However in practice kinetics can make achieving thermodynamic equilibrium occur over geologic timescales or longer. In the case of pure silica (SiO2) at room temperature, the kinetics of a glass to crystal transformation is very slow, and the timescale is on the order of hundreds of millions of years. It is difficult to measure the rate directly at room temperature because in a lab setting nothing measurable happens within a human lifetime.

The reason silica forms glass is that at an atomic scale, each Si4+ ion shares one electron with each of four O2- ions, forming a tetrahedral ionized molecule. Each O2- ion bonds with two Si4+, linking two silica tetrahedra at a common vertex. Because the oxygen ion bonds are relatively flexible, the tetrahedra have only a vaguely preferred orientation with respect to one another; very little energy is required to knock them out of alignment during cooling. Thus, as a body of silica cools from the liquid phase, it can take a long time for regular, periodic crystals to form and settle in, and instead the vibrating atoms may slow down in whatever arrangement the tetrahedra happen to be in, which may or may not be a periodic lattice.

Therefore, if the cooling rate is slower than the crystal forming rate, a crystalline solid forms. On the other hand, if the cooling rate is faster than the crystal forming rate, an amorphous solid forms: glass.

Now to address your questions:

What kind of temperatures would have to be achieved to do this to a temperate area?

Assuming the entirety of your glass precursor material is pure silica (SiO2), the melting point is approximately 1700 C. Other components in solution with silica such as alumina, magnesia, and iron oxides will generally serve to reduce the melting point, however, alumina and iron oxides will make it much easier to crystallize the material as it cools. Beware, as you would want to maintain a temperature above 1700 C long enough to heat everything beneath the surface above the melting point as well, or you will only get a superficial layer of liquid.

In practice, artificial glass forming techniques take advantage of what are called network modifiers, which are metals with valences of 1 or 2, that disrupt the tetrahedral structure even further than it is in pure silica. This (1) reduces the melting point, requiring less energy to form the glass, (2) baffles the ability of the glass to crystallize, meaning even lower cooling rates are required to form glass instead of crystal, (3) reduce the glass viscosity at every temperature, making it easier to shape. So if you have a lot of Group Ia and IIa elements in your precursor material, e.g. lithium, sodium, calcium, magnesium, etc., then more glass will probably form from the same event.

One thing to worry about is that heating 250K sq. mi. to any significant depth involves a tremendous amount of heat, and the heat in that much volume will take a very long time to dissipate into the rest of the planet, its atmosphere, or out into space. We are talking somewhere in the range of thousands to millions of years depending on depth. As a point of reference, a 50,000 pound steel casting can take a day to completely solidify, and possibly a week or more to cool to shipping temperatures. We are talking about possibly trillions of tons of material heated to the same temperatures. In that time, it is possible for lots of defects to show up in the glass for a variety of reasons, most notably ejecta returning to the surface.

There is also the problem of crack formation from volume changes on cooling. Cooling materials decrease in volume as they lose heat, but the glass crater surface also wants to stay put due to friction from its own weight on whatever material it is sitting on. There is thus a competition between the force of cooling-induced shrinkage, and friction. Something has to give to balance forces, and so the material will fracture, and many cracks will form in a single-piece glass crater. Unfortunately, if allowed to cool under its own devices, in other words an excruciatingly slow cooling rate, most of these cracks are going to be small and spaced on the order of inches apart, effectively breaking up your glass surface into little chunks. However, if you can magically cool it instantly throughout its entire volume, it will form cracks only spaced very widely apart. It will also form a glass to a greater depth into the ground. With magic, you could potentially have what is effectively a crater filled by an ocean of glass.

My recommendation is to have a near-pure silica-sand desert, and a very large, very high-temperature magical effect (above 1700 C). Silica is incredibly common on Earth, so it is plausible if your planet is Earth-like. Very large meteor strikes would satisfy the magical heating effect nicely, as would a firestorm, or a radiant "explosion" of some sort. If you want large contiguous pieces of glass instead of a crunchy thin bed of glass fragments, try following the high-temperature magical effect with a rapid cooling magical effect. Faster cooling will give bigger, deeper chunks of glass.

Would the event have to take place in an area that was a desert in the first place? Is sand required?

Sand is not required, but silica is virtually required for what one might call "practical" methods. With magic, other materials are possible.

So you could possibly get away with silica-based rocks, from which silica-sand would be made. Other oxide materials may form glasses, but are much less common on earth than silica. If your world is Earth-like, you may want to just stick with silica.

In principle, any inorganic solid can form a glass if you cool it fast enough. Unfortunately for us, the materials must be either cooled extremely rapidly (106 Kelvin per second or faster for pure metals), or baffled from forming crystals as with silica. It is possible to get metals to form glasses, but the entire volume of pure metal must be cooled more rapidly than is possible by any method known, with the exception of samples that have ~10 nanometer thicknesses or less.

Specialized, artificial, and often very expensive alloys have been developed which require cooling rates ranging from 105 K/s down to 1 K/s. Current iPhones have a small part (the sim-card ejector) which uses an iron-based alloy called liquidmetal that I would guess requires approximately 10 K/s to form a glass. It is also both incredibly strong and incredibly tough compared with crystalline iron alloys. However, as noted on their (site), production sizes are limited by the cooling rates achievable.

With appropriate magic, and a lot of processed iron metal, you could have a basin full of amorphous iron! What I wouldn't give to be able to make that happen on Earth, admittedly at smaller scales and in a controlled, repeatable and inexpensive fashion.

What would be the global impact of such temperatures in a localized area?

As noted above, all that heat has to go somewhere. A meteor creating a crater the size of Texas would cause global devastation and mass extinctions. The planet's climate would be altered for tens of thousands of years or longer. It is implausible survivors would ever see the glass basin before it is broken up and buried by geological action. It is arguably implausible for there to be human survivors with any notion of civilization without some serious magical intervention anyway.

On the other hand, if it is some sort of radiant heating effect, it would be more locally destructive, but would still create massive weather effects including likely global storms, evaporation of nearby bodies of water causing more overcast conditions and rain elsewhere in the region or world, earthquakes from the sudden change of the shape of the ground as well as the huge expansion of matter from heating. Global storms could create problems on the ocean as well, including larger than normal waves. There would be noticeable effects worldwide even with a radiant heating effect, though to a much less severe degree than with a meteor.

Alternatively, you could, as I've mentioned, use a rapid cooling magical effect to remove a lot of the heat instantly, though I suppose this may not fit into your world. If you choose this option, however, that would be sufficient to explain away a lot of the problems associated with a sudden influx of heat and energy into a large chunk of your world. There would plausibly be mild to no long term climate or weather effects in such a scenario. It's possible people thousands of miles away would hardly notice. However, it should be obvious that no matter how this happens, everyone and everything in your Texas will be vaporized or melted into an unrecognizable and meaningless state.

IN SUMMARY

The way I would do it is using molecular-scale magic effects. I recommend a widespread molecular heating effect sufficient to heat a large grassy region down through much of its bedrock. This would then be followed up immediately by the exact same effect but with cooling instead of heating, and much faster (read: instantaneous). This is effectively the only way to make this result in large contiguous chunks of glass while staying consistent with Earth-like physics and material science.

On a side note, this is starting to sound like a scene in a novel set in the Dragonlance campaign setting circa 2nd edition that I read 15 years or so ago. Unfortunately I don't remember the title of the novel, or any of the character names, so I can't really help you identify it, unfortunately. In the scene, a character was walking through a(n in)famous region where a powerful magic-user had used very large-radius, powerful, elemental magic to create a firestorm and an icestorm (possibly among other effects), to stop an opposing army, with the icestorm last. The freezing effect ended up being permanent, and the magic-user and what was left of the army were frozen in place forever. So, a bit similar to what you're talking about, but with ice instead of silica glass.

Edit: I forgot XKCD What-if? has this article, the latter half of which describes the ancient Chicxulub impact (Wikipedia). The area of the crater is considerably smaller than Texas, at about 5%. Munroe describes ejecta reaching space in a similar explosion.

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  • $\begingroup$ -1 Silica is not required. Although it helps. Please fix so I can +1 you. $\endgroup$ – Black Nov 8 '14 at 19:51
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    $\begingroup$ Edited to fix. Silica is virtually required for practical methods (e.g. a nuke or meteor), but if you have magic just about anything is possible. Also added text about other oxide glasses, but noted that they are less common on Earth than silica. $\endgroup$ – wwarriner Nov 8 '14 at 20:52
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    $\begingroup$ This is a fantastic answer. I am essentially looking for a crater in which the world is turned to glass, then breaks due to quakes and time and forms a desert of teeny glass pieces, great visual effects at sunset in mind. The event will also wreak havoc on civilization around the globe. You gave me everything I need and options to boot. I'd upvote 3 or 4 times if I could. $\endgroup$ – James Nov 10 '14 at 15:00
  • $\begingroup$ What about geothermal vents under a silica desert during an ice age? Then, after the ice age has ended... a glass desert ? Or would annealing from repeated heating and cooling be more likely to form a crystalline desert? Although, if you're willing to use magic, then why not geo-engineering (i.e. controlled use of geo-thermals to produce a glass desert by an ancient race) so each area only experiences one round of heating/cooling? $\endgroup$ – EHR Oct 25 '15 at 18:36
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Well we already have volcanic glass and a specific type Obsidian which occur naturally from volcanoes, this glass

is the amorphous (uncrystallized) product of rapidly cooling magma

So there is one source. The Trinity test left

The desert sand, largely made of silica, melted and became a mildly radioactive light green glass,

It was a relatively small blast, 100-ton and only had a 30 ft. wide hole 5 ft. deep.

So unless someone, or something 'glassed' an area, say with a huge laser or some kind of nuclear explosion, the most likely scenario would be to have a very large volcano or a chain of them to 'create' the glass.

What would be the global impact of such temperatures in a localized area?

Considering the impact of a Super-volcano on the world's ecology, weather and local area (Yellowstone is ~1500 sq. mi.), and it is still significantly smaller than the state of Texas (268,820 sq mi), it would likely be or cause an extinction event. The heat dissipation could take generations to cool.

ETA: one more thing

If you have magic, some kind of clash of powerful being like devils and gods perhaps, could have left this wasteland behind, the glass might even have been caused by their destruction.

The event will be magical in nature, but that doesn't mean that a hellish firestorm couldn't cause problem globally.

In that case it would be a LOT of energy that would need to be dissipated, the heat output alone could disrupt trade wind patterns. Also that is a very large area, and that will be an awful lot of smoke, soot and ash from everything burning that can. It could cause some major weather and season issues until everything falls back out.

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  • $\begingroup$ this doesnt really get to the questions I asked. I am not looking for an event, just what the event must entail and whether it can realistically happen within the laws of physics/chemistry $\endgroup$ – James Nov 7 '14 at 16:52
  • $\begingroup$ @James added a little more. $\endgroup$ – bowlturner Nov 7 '14 at 17:05
  • $\begingroup$ @James added a little more based on your 3rd edit... $\endgroup$ – bowlturner Nov 7 '14 at 18:18
  • $\begingroup$ very nice +1 for the deific conflict note...are you stalking and/or hacking me? $\endgroup$ – James Nov 10 '14 at 15:03
  • $\begingroup$ @James Thank you! Well with the level of destruction you are talking about, anything short of deities fighting would make me wonder what kind of power your mortals had! :) $\endgroup$ – bowlturner Nov 10 '14 at 15:09
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Sand and Glass are both made of silica, sufficient heat can convert sandy desert terrain into glass.

From wikipedia:

Trinitite, also known as atomsite or Alamogordo glass, is the glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico. The glass is primarily composed of arkosic sand composed of quartz grains and feldspar (both microcline and smaller amount of plagioclase with small amount of calcite, hornblende and augite in a matrix of sandy clay) that was melted by the atomic blast. It is usually a light green, although color can vary. It is mildly radioactive, but is safe to handle

This article also says:

In 2005 it was theorized by Los Alamos National Laboratory scientist Robert Hermes and independent investigator William Strickfaden that much of the mineral was formed by sand which was drawn up inside the fireball itself and then rained down in a liquid form.:

So essentially you need to pull the sand up into or expose it to a very hot fireball and then let it rain or flow over the area you want covered in the glass.

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Bowlturner beat me to what was going to be the crux of my answer, so I'll go in a different direction.

Would the event have to take place in an area that was a desert in the first place? Is sand required?

Well, it would be a plus. from Wikipedia:

The most familiar, and historically the oldest, types of glass are based on the chemical compound silica (silicon dioxide), the primary constituent of sand.

Silica ($\text{SiO}_2$) - based glasses are typically one-half to three-quarters silica. The highest listed is oxide glass (90%), and the lowest listed is aluminosilicate glass (57%). So, yes, you would want to have a lot of silica - and thus sand - in the area.


What kind of temperatures would have to be achieved to do this to a temperate area?

Locally, you'd want a forecast of sunny, with a high in the upper 1650's (degrees Celsius). Wikipedia indicates that your scenario involves vitrified sand, which can form at that temperature and become glass-like. The page notes that types of vitrified sand can form from interactions with lightning, nuclear detonations, or meteor strikes (note that it does not cite sources, but these events seem plausbile). I'd aim for a couple thousand degrees Celsius. The page also notes that volcanic glass does not fall into this category.

It can be 'more' glassy in the middle and only partially towards the edges.

I think you'll need the high-temperature meteor strike for that scenario.


What would be the global impact of such temperatures in a localized area?

Well, a meteor strike would be devastating. I'd predict a large crater, as well as other effects, such as an impact winter. A lightning strike wouldn't be on the scale you asked for, so that's out. A nuclear explosion - eh, not really large-scale. So I think your only plausible option is the meteor, which will have severe global effects.

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If you want large chunks of glass, it's not possible.

To create glass, you need to heat a material up above its melting point, and then cool it rapidly enough that it solidifies without being able to form a crystalline microstructure. This pretty much requires a rapid, shallow heating such as you'd get from a lightning strike or an atom bomb detonation, and precludes getting any great thickness of glass.

Material is pretty much irrelevant: effectively any material that melts (instead of sublimating or combusting) can be made into a glass if you cool it fast enough. Some materials (such as silica) are more forgiving of cooling rate than others (such as iron).

If you want a thin layer of glass (no more than an inch or two thick), you can do it through simple magical heating, though you might have trouble cooling the center of your area fast enough. If you want something thicker, you'll need to go with direct magical transmutation.

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  • $\begingroup$ +1 Despite all the definitions flying around you're the only one that pointed out that you don't need silica. Good coverage of the issues as well. $\endgroup$ – Black Nov 8 '14 at 19:50
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This is more an answer towards obsidian rather than sand, although there are several volcanic 'glass' rocks out there...tachylite (I think thats right)...even Pumace is considered a volcanic glass.

To form volcanic glass, you need a lava flow to cool extremely quickly. The lava content can range from high silica content (obsidian) to something with a much lower silica content (tachylite) along with several types in between...so content of the lava doesn't seem to matter as much as the extremely quick cooling. What better way to cool lava than water? Sea volcanoes are quite frequently responsible for volcanic glass.

Try to give a scenario for it:

Somewhere in early planetary history, a volcanic hotspot exists under a significant amount of water. A single eruption occurs and the magma released turns into glass as the water quickly cools it. Over an extended period of time these eruptions leave layer upon layer of volcanic glass deposits. Enter plate tectonics...these layers of volcanic glass exists between two plates and gets pushed up to the surface as the two plates collide (not unlike the Himalya's when the Indian subcontinent merged with Asia). Volcanic glass is hard, but exceedingly brittle...all you would need now is an impact or geological event that shatters the majority of the volcanic glass. I like the idea of a meteor impact at this time, which would break up the glass and leave behind a crater like lake for the glass to collect in afterwards.

Or perhaps more to your want here...the volcanic glass layers have a layer of dirt collect on top of it, leaving it a lush green location (igneous rocks are rich in minerals that plant life thrives on, if you've ever seen Hawaii, the color of these greens are absolutely amazing) and you have a civilization that builds on that location. How you turn this lush green location with a civilization thriving on it into a glass sea is now your call to make, just make whatever happens contain a large enough concussive impact to shatter the volcanic glass below. I get the strange feeling you're thinking magic here

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  • $\begingroup$ I like the idea of an explosive underwater volcanic eruption for making lots of glass, but I suspect that, over geological timescales and subject to the slow heating and mechanical stress involved in plate tectonics, the glass would just revert back to ordinary crystalline rock. You might be better off having the eruption be a recent event, although then, of course, your glass desert would have to be near the sea. (You might be able to have the eruption occur in an area already experiencing orogenic uplift due to a plate collision, which subsequently makes the sea disappear. Or magic.) $\endgroup$ – Ilmari Karonen Nov 8 '14 at 8:35
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Glass fractures easily. If you want a large smooth glassy area, you would need to make sure the glass layer is thick enough to actually form a molten layer that wouldn't turn to shards in an instant. You would need a steady long heat to make sure you permeate the ground enough to get a decently thick pool of liquid. It'd probably also be helpful to cool it slowly so that it has more time to work off stress as it shrinks.

If you try to do a sudden event, remember that sand is reasonably good at insulating from heat (see desert animals burrowing to escape the heat of the sun). You're going to need quite the firecracker to get a sudden burst of heat very deep.

For some real life comparisons, look at the volcanic glass on Kauai, Hawaii. There are areas where the magma cooled with just the right conditions to form a glassy sheen on the surface. (However, they are not flat, because they crystallized into glass while the lava was moving so they had to follow the outside edge of the lava as it cooled).

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    $\begingroup$ The process you are describing here should result in crystalline structures, not glass. Long cooling periods allow the minerals to separate instead $\endgroup$ – Twelfth Nov 7 '14 at 19:38
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Futuristic science is equivalent to magic. So assuming you can have quantum nano-robots that can convert energy into matter and vice versa these answers should be adequate:

What kind of temperatures would have to be achieved to do this to a temperate area?

Pretty high, 1 kg of matter turned into pure energy is equivalent to almost 21.5 megatons of TNT. In comparison the largest nuclear weapon ever tested (according to wikipedia) the Tsar Bomba exploded at a force of about 50 megatons. However this technology (hopefully) would use all the extra energy to form silica atoms and bond them into glass. Hopefully no extra heat would be leftover.

Would the event have to take place in an area that was a desert in the first place? Is sand required?

No. You could even turn air into glass (compressed first) if you wanted to. This would quickly erode the glass into smaller pieces if done at a high enough altitude.

What would be the global impact of such temperatures in a localized area?

If the laws of thermodynamics prevented turning all of the excess energy into glass: Possible side effects could include vaporization of the world. It could quite possibly vaporize much more than the world if the robots malfunctioned and vaporized all of Earth into pure energy.

Note: Forgive me for poor grammar and for any overlooked laws of nature that distinctly forbid this.

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Read this after reading starrise's excellent summation.

Just as a note: Immanuel Velikovsky in his books Worlds in Collision, Earth in Upheaval, and Ages in Chaos postulated cataclysmic evolution. His idea was that our planetary neighbours were at one time wanderers in the solar system and came very close to earth, creating great catastrophy. The next paragraphs are from the wiki listing of him:

Planet Earth has suffered natural catastrophes on a global scale, both before and during humankind's recorded history.

There is evidence for these catastrophes in the geological record (here Velikovsky was advocating Catastrophist ideas as opposed to the prevailing Uniformitarian notions) and archeological record. The extinction of many species had occurred catastrophically, not by gradual Darwinian means. The catastrophes that occurred within the memory of humankind are recorded in the myths, legends and written history of all ancient cultures and civilisations. Velikovsky pointed to alleged concordances in the accounts of many cultures, and proposed that they referred to the same real events. For instance, the memory of a flood is recorded in the Hebrew Bible, in the Greek legend of Deucalion, and in the Manu legend of India.

The causes of these natural catastrophes were close encounters between the Earth and other bodies within the solar system — not least what are now the planets Saturn, Jupiter, Venus, and Mars, these bodies having moved upon different orbits within human memory.

So, just suppose our hypothetical planet had a close encounter with another, it would seem that a sea of molten glass could be created. It at least would result in great volcanic upheaval, and lots of volcanic glass.

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  • $\begingroup$ In other words, magic. Velikovsky was an arch-crackpot, and his stories (they do not deserve to be called "theories") involve violation of the laws of physics on a super-biblical scale. $\endgroup$ – Beta Nov 9 '14 at 18:04

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