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This is a work of fiction. All the characters and events portrayed in this book are fictional, and any resemblance to real people or incidents is purely coincidental.

Recycling—From Stars to Starships © 2021 by Jim Beall

When Is An Hypothesis Not An Hypothesis? When it’s the Solutrean Hypothesis © 2021 by Michael Z. Williamson

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Recycling—From Stars to Starships
by Jim Beall

Stars recycle and so must we if we are to travel between them.

Supernova Remnant Cassiopeia A	Nauvoo Generational Starship	
Image credit: NASA/CXC/SAO	Image credit: expanse.wikia.com	

Stars have practiced recycling from near the beginning
The ordinary matter of the early universe was mostly hydrogen with some helium. Population III stars formed out of that primordial mix (with trace amounts of lithium and beryllium) and fused more hydrogen into helium. Those stars had comparatively short lifespans ending in supernovas (or other stellar events such as becoming black holes) and spreading heavier elements into space where they—along with hydrogen—became part of Population II stars. (NOTE 1)
Science fiction author Larry Niven introduced an alien species ("Outsiders") in his short story "Flatlander" (1967) who were helium II beings, perhaps dating back to those first populations of stars.
When that next generation of stars ended with supernovas (or other stellar events) of their own, still heavier elements were ejected into space. The Sun is a Population I star. That is, based on spectral analysis, some of the elements contained within its mass have been recycled from at least two previous stars.
Novas and supernovas have long been a staple of science fiction, especially weapons that can cause them, whether it be nova bombs (Andromeda), trilithium torpedoes (Star Trek), or even weaponized gravitational drives (The Armageddon Inheritance, 1993, by David Weber). Sometimes the solar event is inadvertent, such as in "Time Fuze" (1954, by Randall Garret) where Earth's first starship learns to their dismay that their FTL drive causes nearby stars to nova (including the Sun, as they discover at story end). In another short story, "The Fourth Profession" (1971, by Larry Niven), a visiting merchant race needs humans to build space laser cannons to propel their light sails to let them to proceed to their next stop but, if deals cannot be reached, they have a nova device to use instead.

The Armageddon Inheritance, by David Weber
The Earth has apparently always recycled its crust
Recycling is not limited to stars. The Earth recycles its crust, and apparently always has. The ratios of certain elements (e.g., germanium and silicon) in samples taken from the basalt deposits of mid-oceanic ridges all over the world indicate that crust material remelted by subduction spreads evenly throughout the mantle and must have been doing so throughout most of the planet's history. (NOTE 2)

Mantle Recycling
Source: United States Geological Service—Public Domain
The recycling mechanism—subduction—is part of plate tectonics (originally called "continental drift"), which was itself considered fiction or even fantasy by most authorities. Abraham Ortelius (NOTE 3) and other early cartographers, as well as explorers such as Magellan, had noted that sections of continents appeared to line up with others. The edge geologies appeared to match, and paleontologists also identified similarities in the fossil records. Nonetheless, when Alfred Wegener formally proposed continental drift in his 1915 paper, Die Entstehung der Kontinente und Ozeane (The Origin of Continents and Oceans), many authorities summarily rejected it due to the absence of any known "force that could move continents." (NOTE 4)
By the mid 1960s, the discovery and validation of seafloor spreading led to widespread acceptance of plate tectonics by the geoscientific community.
Science fiction and fantasy stories have long featured plots and characters with vulcanism and earthquake elements and abilities, respectively. Plate tectonics soon became another such world-building and plot element. Hardly a decade after the official recognition of plate tectonics, Larry Niven's Protector (1974) had the last "protectors" on their abandoned homeworld induce plate tectonic and other planetary disturbances to make their planet's interior metals accessible for the construction of their space fleet.

Protector, by Larry Niven
Image credit: Wikipedia
In David Brin's Startide Rising and Uplift War (1983 and 1987), planets are allowed to "go fallow" and renew their entire ecosystems and surfaces (via tectonic plate subduction and other mechanisms) to facilitate the possible rise of new species that could be uplifted to sentience. More recently, the Broken Earth trilogy by N. K. Jemisin used "geoscience fiction" and plate tectonics throughout as a central theme of the entire series. The world is subject to periods of geologic instability, and the central characters are those with genetically-engineered abilities to affect those forces.

Humans have always recycled
Whether fashioning huts with reeds or crafting tools out of stone or bone, humans have always practiced recycling. This practice included reusing the building materials of the great majority of the structures of antiquity. Those exceptions that did survive did so for a variety of reasons. The Pantheon (Rome), for example, has been in continuous use since construction nearly two millennia ago. (NOTE 5) Some, such as Machu Picchu (Peru), were in locations sufficiently inconvenient or remote as to discourage efforts to reuse their materials. Others, like Palenque (also called "Lakamha," Mexico) were abandoned and their sites largely reclaimed by nature.

Palenque, Mexico
Image Credit: G. Mannaerts—Wikimedia Commons
Many such ancient sites were "rediscovered" by Western adventurers and archaeologists within the last century or so (NOTE 6). Science fiction has long had as a meme the discovery and exploration of the ruins of ancient, advanced civilizations. Perhaps the earliest example was the 1827 novel by Jane Wells Webb, The Mummy! (NOTE 7) The fictional adventures of "Indiana Jones" and "Lara Croft" ("Tomb Raider") have continued that practice.
One of the author's science fiction favorites that features exploring a long dead civilization is Galactic Derelict (1959, by Andre Norton), in which characters inadvertently activate a spaceship that takes them on an involuntary grand tour of ancient sites. Another particularly notable example that involves exploring a long-abandoned site of a still existing and advanced race is Frederick Pohl's Gateway (1977). (NOTE 8)
    
Image Credits: Wikipedia
More recently, the movie and television series "Star Gate" featured current day characters who activate ancient abandoned technology only to find that the builders are still quite active.
Other buildings from antiquity have survived only in part. That is, what remains today are the materials least valuable, accessible, or portable. The most prominent examples of this are the pyramids of Giza (Egypt). It is instructive to note that they were originally smoothly surfaced with huge, incredibly engineered, hand-polished casing stones of white limestone. The number of man hours required for this one sub-task has been estimated to be in the millions. (NOTE 9). As originally constructed, they must have seemed to glow as they dominated the horizon for miles in all directions.

The Great Pyramid of Giza
Image Credit: Budget Direct (NOTE 10)
The Great Pyramid of Giza (aka, the Pyramid of Khufu or the Pyramid of Cheops) remained essentially externally intact until the great 1303 Crete earthquake shook some casing stones free and opened cracks allowing tools easier prying access. By 1356, many of the casing stones had already been recycled into structures in nearby Cairo. See the image below of one of the surviving casing stones.

Jon Bodsworth, Copyrighted free use	Same casing stone, circa 1912	
Wikimedia Commons	Public Domain	

High quality stone was also a valuable resource for more than reuse in new buildings. For example, consider the anchor below:

3,400-year-old Egyptian anchor on display at the Israel Museum
(Photograph credit: Laura Lachman)
The decoration on the anchor depicts a woman writing on a tablet. The symbol above her head identifies her as the goddess Seshat, the ancient Egyptian deity of writing, and the hieroglyphs contain the traditional divine attribute: “Mistress of the house of books.” The style and hieroglyphs indicate that the beautiful, polished limestone slab would have adorned the wall of a major Egyptian shrine during the Late Bronze Age, roughly 3,400 years ago, before it began its "second career" as a boat anchor. (NOTE 11)
Most of the pyramids' structures remain available for viewing and study, but the recycling of buildings has long posed challenges for archaeologists because the process makes historic sites effectively "vanish." Overhead photographs from aircraft and, more recently, drones have proved immensely helpful in finding such "lost" structures. The soil in fields is shallower over residual foundations than normal, but deeper than normal over trenches, pits, and dug out buildings. These differences are plainly visible, especially during periods of drought.
The resulting variations in vegetation growth produce ghostly blueprints of the buildings themselves, complete with interior wall lines. Below is an overhead photograph from a typical location, and a sketch depicting the process.
 
Images source: Wikipedia
In effect, the markings on the ground reveal the extent of the recycling. If the stones or bricks in the wall (or road) were removed but the foundation or bottom courses left in place, then the shallow soil yields lower growth of vegetation (pale strips or lines). If all the stones were dug out, then greater soil depth allows greener or thicker plant growth than normal. In the first image above, the light stretch on the left marks the road, whose rocky subsurface remains under the grass. The thinner pale lines on the right show were walls once stood but their foundations remain, revealing in the shorter grass a virtual blueprint of the building that was there.
Finding and investigating these patterns have led to numerous archaeological finds over the last few decades. In some cases, onsite investigations have revised the understanding of local history. Many other excavations have revealed that sites were reused period after period, such as a known Iron Age site having been previously occupied in the Bronze Age, and perhaps even in the Neolithic. The long running British Time Team television program (NOTE 12) documented hundreds of such cases during their real-time digs. (NOTE 13) In each such case, it is the site itself that was recycled.
As noted previously, humans have generally recycled everything that they conveniently or profitably could. (NOTE 14) In fact, declining to recycle has been a luxury, including deliberately preserving sites on cultural or historical grounds. A new motivation has emerged to encourage preservation: tourism. Ecotourism is a rising revenue source world-wide, but archaeological tourism is centuries old (NOTE 15) and continues to grow strongly. Greece, with all its preserved temples and monuments, derives about one-fourth of its annual gross domestic product (GDP) from tourism. Egypt gained about eleven percent GDP from archaeological tourism while employing about fourteen percent of its population from tourism, until terrorist attacks on foreigners began greatly reducing the numbers of visitors.
Perhaps an even better indicator of the expansion of archaeological tourism—and its associated economic boons—is that remote and difficult to access Machu Picchu drew over one and a half million visitors in 2018. In that same year, partially cleared Palenque had nearly three-quarters of a million visitors, and the total for all archaeological sites administered by Mexico's Instituto Nacional de Antropología e Historia was nearly seventeen million. Meanwhile, the number for Angkor Wat was over two and a half million.
The process of recycling large blocks of stone includes demolishing, digging, and transporting. Re-users would only choose to do it if they did not have a better option. This was usually an easy economic decision when a new structure replaced the old on the same site, but many times this was not the case yet recycling was done anyway. Quarrying hard rock with only hand tools simply required so much labor that suitable existing stones were still worth the effort even if their next intended use was a considerable distance away.
Quarrying is also slow and, even with recycling, would be challenged to support a prosperous growing civilization. The need for structural materials naturally increases with human population and their standard of living. Thus, successful and expanding human polities have always consumed progressively greater amounts of whatever was used for buildings, with higher status portions of their societies demanding more and better prestigious construction elements.
This brings us to Rome, and concrete.
Romans were not the first to invent concrete (NOTE 16) but their empire grew to such a large size in area, population, and urbanization that neither harvesting wood nor simply quarrying stone would have sufficed to meet their needs. Roman engineers turned to concrete as the key building material, including for elite structures like the Pantheon, the Coliseum, and major aqueducts.
Recovering large stones allows their reuse in high quality structures, but attempts to recycle concrete (especially with lower tech tools) generally result in rubble adequate only for prosaic applications such as fill or road beds. This, perhaps serendipitously, is one of the major reasons why many historic Roman structures have survived into the present day. That is, they would have been expensive to demolish and would have yielded little in the way of valuable material.
Two of the key elements were recycling volcanic ash (e.g., Pompey and Vesuvius) and high temperature kilns (~1700 degrees Fahrenheit). (NOTE 17) When Rome fell, the making of concrete was among the many scientific and engineering "secrets" that were lost. (NOTE 18) Over a millennium would pass before a process to make satisfactory concrete would be rediscovered. (NOTE 19)
If science fiction authors want an easy way to create a major alternate history, all they need do is postulate an earlier rediscovery of how to make concrete. Historically, manuscripts by the Roman Pollio Vitruvius (who died circa 15 AD) that contained a section on Roman cement manufacturing were rediscovered in 1414. They would be translated and republished around 1450, and gradually spread across Europe. This revived the interest in concrete and Fra Giocondo would use Roman style cement to build the pier of the Pont de Notre Dame in Paris in 1499, the first modern use of concrete. Those same Roman manuscripts could easily have been retranslated centuries earlier than historical, as several dozens of other copies survived the fall of Rome and still existed throughout the Dark Ages.
One more aspect of concrete is worth noting. Where Romans used volcanic ash, modern concrete makers have commonly used coal power plant fly ash. This allows coal plants to harmlessly recycle that waste product in an environmentally safe and useful way. The decreasing number of operating coal plants has posed a problem for the concrete industry.
Before turning to modern recycling, glass merits a special mention. Glass has a long history but is much easier to recycle (with low technology) than make from raw materials. For example, glass appears not to have been domestically produced in Britain until at least two centuries after the Romans left. (NOTE 20) However, archaeologists have found considerable amounts of Roman glass in Britain, along with sites where shards of Roman glass were remelted to make new objects. Given the relative fragility of the material, it appears likely that a significant fraction of all the glassware used in Roman Britain were made from recycled material.

Recycling is even more important today
Recycling remains an easy decision when there is profit to be made, with aluminum a leading example. Despite being the most common metal in the Earth's crust (eight percent), refining costs made it so rare that it was used as jewelry as late as the end of the 19th Century. Bulk use of aluminum appeared fantastical and, indeed, Jules Verne had an aluminum rocket in his 1865 Journey to the Moon.
When the U.S. Army Corp of Engineers needed a "perfect" material for the apex of the Washington Monument, the performance requirements and the desire to be impressively unique made aluminum by far the best choice. The nine-inch, 100 ounce pyramid casting was, in 1884, the largest piece of aluminum in the world. It would take Charles Martin Hall's revolutionary electrolysis refining process coupled with George Westinghouse's electrical harnessing of Niagara Falls to make aluminum practical for other uses. (NOTE 21)
Recycling aluminum takes about 8% of the energy required to mine and refine bauxite to make aluminum. With this sort of economic incentive, it should come as no surprise that nearly 75% of all the aluminum ever produced is still in use today. (NOTE 22)
The statistics are equally astounding for steel. According to the Steel Recycling Institute, steel "is the most recycled material on the planet, more than all other materials combined" with about 86% of steel being recycled. Yet, despite that level of success, the growth of planetary population and standards of living still requires about that one-third of all steel must be produced from raw materials. (NOTE 23)
Sometimes recycling is essential simply to deal with a durable product used in bulk and discarded in bulk. Vehicle tires may head this list. In this country alone, about one tire per person is discarded annually, or somewhat over 300 million per year. Despite some early recycling efforts, this led to enormous piles of tires building up all over the planet with the total number of discarded tires reaching about one BILLION in the United States in 1990, with perhaps an equal number in other countries around the world. (NOTE 24) Many sites covered so much area that they were visible from orbit. (NOTE 25)
Significant progress has been made in recycling tires. According to the EPA and the U.S. Tire Manufacturers Association (USTMA), over 80% of annually discarded tires now undergo recycling, 90% of those tire piles have been abated, and U.S. discarded tire inventories have been reduced from over one billion to perhaps seventy-five million. For example, one site in Colorado once had an estimated 80 million tires piled up and became known as "Tire Mountain." The picture below shows the "Tire Mountain" site after substantial reduction has taken place. The remaining tires are in cells of one million each separated by fire walls of sand and clay. Perhaps "Tire Prairie" is now a more appropriate name.

The remains of "Tire Mountain" in Colorado
Photograph courtesy of John Sheerin, USTMA (NOTE 26)
Tires are engineered not merely to survive adverse weather, repeated impacts, and extreme temperatures, but to perform well under those conditions. Thus, the better the tire, the tougher it is to recycle it. The absence of mechanical shredders sufficiently powerful to process tires in bulk delayed recycling efforts until a merging of three factors occurred. Environmental concerns helped drive research and focus regulating bodies; regulatory actions helped adjust economic factors; and new end uses were found for the processed material.
Currently, the main uses of the processed tire material are fuel, ground uses like athletic field artificial turf, and rubberized asphalt. Tires can also be recycled into cement, serving much of the function of volcanic ash or coal fly ash, but the process requires significant industrial-scale facilities and energy. For example, one stage of the process requires heating the material to 2800 degrees Fahrenheit. (NOTE 27) These are all relatively low value products, but scientists and engineers continue to research better ones, with some recent promising—but preliminary—results. (NOTE 28)
In summary, the performance requirements and long service lives of durable products like stone, concrete, or tires can make them difficult to recycle.

Unlike tires, gold is an intrinsically attractive candidate to recover but, perhaps counterintuitively, its value often makes doing so exceedingly difficult.
The ancient Egyptians displayed gold everywhere, but they had mastered the ability to flatten sheets of gold to as thin as a single micron. (NOTE 29) Since they often used such sheets to clad the visible surfaces of objects, appearances often belied the mass of the precious metal actually present. That is, its very value led to it being applied as sparingly as possible, meaning that one might have to process great quantities of material to gain any meaningful mass of gold. (NOTE 30)
This conundrum continues today. Gold is only one of the many precious metals used in modern electronics, such as smart phones and personal computers. Others include silver, palladium, indium, platinum, and rare earth metals. One estimate is that each year's personal electronics contain another 320 tons of gold and 7,500 tons of silver worth about twenty-one billion dollars. (NOTE 31)
The relatively brief life cycle of personal electronics has resulted in large quantities of such items being discarded every year. The collective mass of the material has become so immense that it has been awarded its own name and acronym, "waste electrical and electronic equipment," or WEEE. Analyses of WEEE piles have revealed that they contain precious elements in greater concentrations that the native ores from which those same elements were originally mined. Smart phones, for example, contain about two hundred times the gold that ore does by weight.
WEEE would appear to be an obvious candidate for economically profitable recycling, but this is not (yet) the case. The necessary processes are expensive and involve hazardous materials. The problem stems from the fact that personal electronics designs concentrate on user ergonomics, visual appeal, and portability. As a result, recycling requires either prohibitively labor-intensive and expensive item-by-item disassembly, or thresher-sized crushing machinery which disperses the tiny valuable bits into the rest of the non-valuable mass. Industrial scale recovery also involves complex pyrometallurgical and hydrometallurgical processes producing large volumes of toxic wastes. (NOTE 32)
One more thing that we must consider for recycling is ourselves. For many, this is an uncomfortable topic but the human population of Earth is nearly eight billion and rising. Many have offered ideas on the subject, including science fiction which has frequently included stories involving overpopulation, cadaver recycling, and other related topics. (NOTE 33) Historically, human societies have employed a great variety of methods but almost all pose some problems, and often unexpected ones. For instance, cremation facilities had to be modified in the United Kingdom when they were discovered to be exhausting dangerous levels of mercury (from dental fillings) to the air. (NOTE 34)
It is not clear how the treatment of human remains will be resolved in the future, but many new potential disposition methods are being advanced. (NOTE 35)

Recycling is a mandate for space travel
Turning to space travel, the early missions did not recycle anything. Stay times in the International Space Station (ISS) have grown to such duration that recycling fluids into potable water has become a necessity. (NOTE 36) Trips to Mars and beyond will doubtless require additional recycling. Basically, the longer the time spent in space, the more that needs to be recycled.
For generational ships (also called "worldships"), the extreme duration of their journey means that recycling must become the dominant design mandate. That is, unless something (or its prebuilt onboard spares) will last for the entire voyage, another will have to be built to replace it, perhaps a great many times. Advances in 3D printing and forging may allow the replacement to be manufactured, but what will be the source of the material? It will not be possible to send along enough spare parts or stock to last the entire voyage. Inevitably, new parts will need to be made out of old ones.
Even if there were enough raw materials to make new parts, there will be no deserts to stack up piles of discarded stuff. Ejecting debris into space is not the answer. Not only would that require thousands of airlock cycles, but the mass will also doubtless be needed later. Nor can recycling be done in any haphazard fashion, as recycling processes that release damaging byproducts cannot be tolerated in a closed environment.
This key conceptual change means that shipboard devices, clothes, furnishings, structures, and everything else have to be designed backwards from recycling. For example, long-distance space travelers may have to use more awkward personal devices, wear only certain fabrics, or accept any number of other limitations if those steps are necessary to optimize recycling.
The most efficient recycling processes involve a great deal of energy. This is not new, as the Romans needed about 1700 degrees Fahrenheit kilns to recycle volcanic ash to make concrete and recycling tires that same way requires about 2800 degrees Fahrenheit. The recovery processes for precious metals also involve the energy input of high heat, as does remelting steel and glass. If that level of energy consumption is necessary for safe and efficient recycling, then the ship design must accommodate it.
Worldships will be constantly recycling throughout their multi-century journeys. Their drives (fusion, antimatter, or other) could easily be tapped to provide recycle power during operation, but finite fuel capacity will certainly mean that the drive will be dormant for most of the trip. Thus, each ship will have to be built with separate, long-lived, and redundant onboard power systems with near-zero emissions. Recycling will be part of the "energy budget," along with life support, operating controls, and scientific work.
Breeder fission reactors are a likely choice for onboard power generation. As they "burn out" their initial fissile fuel, some of the fission neutrons transmute the rest of the core's fertile isotope into fissile ones. (NOTE 37) Periodically, fission reactors need to discharge their fuel, chemically separate and remove the products of previous fissions from the fuel, and reform the fissile and fertile elements into a working geometry. This nuclear recycling is called "reprocessing" (NOTE 38), and yields fresh fuel and many radioactive isotopes ("nuclear waste"). That waste may well be quite useful in its own right because their decay heat and radiation may have many valuable applications (e.g., fuel preheating or material sterilization), as might some of the isotopes themselves in future tech.
The worldship will need to decelerate when it reaches its destination, and will need about as much thrusting force as it took to begin the journey. The thrust equation (force equals mass multiplied by acceleration) means this maneuver will require energy to accelerate and eject mass at the greatest feasible velocity. The ship's drive will supply the energy, but the first source of reaction mass will almost certainly be materials no longer able to be recycled!
Recycling: it's neither exciting nor heroic, but we'll have to do it to reach the stars.
And we'll have to do it damn well.

NOTES:

1) No Population III stars have been directly observed, but are theorized to have formed about a couple hundred million years after the Big Bang with lifespans of only about a hundred million years. See the following link for an overview:
https://www.forbes.com/sites/startswithabang/2017/12/21/when-did-the-first-stars-appear-in-the-universe/?sh=236ede6d3bcf

2) See also here.

3) A portion of that Dutch cartographer's famous 1587 Thesaurus geographicus can be read online here. Note, however, that it is in Latin. Ortelius would offer the possibility of continental drift in his 1596 edition.

4) David Attenborough recounted some of his university experiences during the late 1940s during a broadcast interview in 2012:
"At university I once asked one of my lecturers why he was not talking to us about continental drift and I was told, sneeringly, that if I could I prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed."

5) The Pantheon was finished about nineteen hundred years ago, replacing two previous structures on the same site destroyed by fires, but probably re-used some stone or other foundation materials.

6) Angkor Wat (Cambodia) is often somewhat mistakenly put in this category. In any case the first photographs of that dramatically overgrown site caused quite a stir in the "Western world." Many of those photographs can be viewed here.

7) Originally the author's name was listed as "Anon," because women authors were not particularly marketable or even socially acceptable.  Editor John Claudius Loudon was so impressed by the story that he went to considerable effort to track down the author. He was stunned to learn the author was a woman. The surprise must have been a mutually pleasant one, however, as the two married a year later. The result is that the author of The Mummy! is often listed as "Jane C. Loudon," even though that was not her legal name when she published it. So, even her name underwent recycling.

8) The novel was preceded by the 1972 novella, "Merchants of Venus" and involves discovering ancient structures of the same alien race.

9) The video here includes a master stone cutter re-enacting the process, and also contains video showing how the pyramids would have looked amidst their contemporary environs.

10) See this.

11) The anchor was discovered by a swimmer in the shallows off Haifa:
https://www.jpost.com/israel-news/3400-year-old-egyptian-artifact-uncovered-in-israel-on-display-in-jerusalem-616337
Trapezoidal stone anchors were hardly uncommon during that period. See also this.

12) Time Team was first broadcast in 1994 and, in its original form, ran for about 20 seasons for a total of 280 episodes. Many can be found on-line here.

13) Time Team became extremely popular in the British Isles, and was credited with reawakening wide-spread interest in British history. The show's presenter, Tony Robinson, who first rose to fame in the comedic Black Adder series, was knighted in 2013 for his "lifetime of public and political service with a career as an actor, theatre director, children's author and television presenter."

14) Perhaps the ultimate example of recycling, however, remains science fiction's Ringworld (1970) in which a star's entire solar system was recycled to create the Ringworld orbiting it.

15) For a retrospective of vintage pyramid tourism, complete with photographs (including sitting for tea atop the Great Pyramid!) see this.

16) Structures of several earlier civilizations show that it was discovered many other times, with perhaps the earliest about 6500 BC in the Middle East. More on the history of concrete can be found here.

17) An outstanding summary of the history and development of Roman concrete engineering can be found here.

18) During the first decade of this century, the U.S. nuclear industry identified that an eerily similar situation was underway. Specifically, the number of people was dropping rapidly who were skilled in the crafts required to build large nuclear plants, whose construction had dramatically declined after the 1979 Three Mile Island accident and soon essentially ceased altogether.

19) The millennium-long ignorance of concrete after the Fall of Rome (476 AD) had many consequences. For example, it is probably why all the great medieval cathedrals of Europe were built out of stone, and why it took centuries to complete them. By comparison, the spectacular and largely concrete Pantheon took less than a decade to build well over a thousand years earlier.

20) Source.

21) One of those "other uses" was the Wright Bothers' planes, which were able to get off the ground because their engines were machined out of lightweight aluminum.

22) Source.

23) Source.

24) Source.

25) For example, Sulaibiya, Kuwait tire dump from space see this.
There are many images and videos on the internet showing enormous tire dumps blighting landscapes all over the world. For a positive example of a tire created image visible from space, see this.

26) John Sheerin is the Director, End of Life Tire Programs, U.S. Tire Manufacturers Association (USTMA), see this.

27) This video shows the process, including the size of the recycle complex. A good overview is presented starting at time = 15:47. Note that the top of screen at time 16:00 indicates that part of the process is consuming 27.9 megawatts (MW).

28) See here and here.

29) Source.

30) Plastics pose a recycling challenge that resembles an intersection of gold and tires. That is, each individual plastic item (like a grocery bag) contains very little material (like gold) but they are discarded in such great numbers (like tires) that they accumulate in eco-destructive masses.

31) Source.

32) For an excellent summary and overview, see this.
Perhaps a better way to illustrate the WEEE challenges, is follow one entrepreneur as he recovers the gold from a single computer here.
(Spoiler alert: he gets one tiny "bb," worth a bit over two dollars.)

33) Three disparate examples: Dune (1965, novel by Frank Herbert), Soylent Green (1973 film), and "The Mark of Gideon" (Star Trek episode, originally aired 1969).

34) See this.

35) For a discussion of several such options, see this.

36) See this.

37) Uranium reactors currently use Uranium-235 as the initial fissile isotope, but could also use Plutonium-239 or Uranium-233. Thorium reactors use the same initial fissile isotopes, but transmute fertile Thorium-232 into Uranium-233.

38) Citing nuclear weapons proliferation concerns, the U.S. ceased reprocessing of commercial nuclear fuel over four decades ago. Many other nations continue to reprocess nuclear fuel.

Jim Beall (BS-Math, MBA, PE) has been a nuclear engineer for over forty years, a war gamer for over fifty, and an avid reader of science fiction for even longer. His experience in nuclear engineering and power systems began as a naval officer. Experience after the USN includes design, construction, inspection, enforcement, and assessment with a nuclear utility, an architect engineering firm, and the U.S. Nuclear Regulatory Commission (USNRC).

When Is An Hypothesis Not An Hypothesis? When it's the Solutrean Hypothesis.
by Michael Z. Williamson

I’ve done a lot of research on the Upper Paleolithic recently, for my novels A Long Time Until Now, That Was Now, This is Then, and for an upcoming third.
I have several friends enamored of this hypothesis, and I’m not sure why. Pretty much no credible researchers like it, and I find it utterly uncompelling on every level. I looked at it again after a recent debate. I like it less every time I look at it.
It summarizes like this: The Solutrean Culture of the area that is now France and Spain, (22,000-17,000 BP) used overshot flaking to shape their flint tools, and as of the proposal date, were the first culture to do so. Clovis points (13,200 BP) of the Americas also used overshot flaking. Lots of Clovis points are found in the Eastern U.S., therefore, the Solutreans must have travelled across the Atlantic, and settled there 3800 years later with the same technology. In support, it is argued that the oldest settlement sites in the Americas are in the Eastern U.S.
That's it.
So, starting at the beginning:
The oldest probable human occupation in the Americas is 24,000 BP, in the Yukon. There are numerous confirmed finds older than the Clovis, all the way down to Chile. There are speculated and potential sites as far back as 50,000 BP, but those are not confirmed. Still, there were plenty of people in the Americas before the Clovis Culture (more accurately, it's a tradition or industry, since we find it all over and they very well were entirely different cultures with different languages, just using the same technology, much like Japan, the U.S. and Germany all use the same steels and machine tools to make cars).
We find more settlements in the east (and the ones my friends referenced are pre-Clovis). But settlements require both terrain and climate to support them. Finds from nomadic peoples are hard to source, because they are widely dispersed on terrain that's not used much. So the number of finds is less significant than the contents.
Meadowcroft Rockshelter includes: "other lanceolate points, small prismatic blades, and small polyhedral blade cores have been recovered. According to Adovasio et al, this complex has a Eurasiatic and Siberian appearance." And predate the Clovis points by 3000 years, but don't resemble the 1000 year older, or possibly contemporary, Solutrean points.
Topper Site predates Clovis, and bears no resemblance to Solutrean sites that are only about 1000 years older.
Cactus Hill dates positively to at least 15,000 BP, possibly 16,000-20,000, but that is not confirmed. It contains two overshot-flaked partial (broken) points that may be proto-Clovis. This is the primary basis for the claims of the Solutrean Hypothesis. Two broken pieces of points that are admitted to not be Solutrean, not Clovis, but possibly similar in some ways to both. Best case. Worst case, they're flaked points that bear no similarity to Solutrean Points at all.

Source: Wikipedia.org
The major sites are evenly split between east and west North America, with the west averaging older, but not relevantly so. This suggests a quite thorough occupation of the continent. Actual coastlines and the Great Lakes and Canadian Shield regions suffered much change in shape due to rising sea levels (narrower in the west), the melt and runoff of Glacial Lake Agassiz, and other factors. It's going to be harder to find evidence in those locations.
Interestingly, the later Cascade Points of the Pacific Northwest bear more of a resemblance to Solutrean Points than Clovis Points and support the reasonable deduction that there are only so many ways to shape a stone point, so similarities should be expected.
The theory of a land bridge in Beringia is well-supported by numerous finds. There's a current dispute over an ice-free corridor in the right timeframe for Clovis occupation, but it's not a problem for the confirmed earlier settlements. It also has no bearing on coastal migration, and most of those sites are under water now, though some are starting to be located and explored, and that will probably settle this permanently.
The Clovis industry shows up when it does and becomes widespread across the continent. It's a very effective, efficient, and beautiful way of making lithic points.
So, accepted as fact: There were peoples in the Americas for at least 5,000 years before Clovis, probably 11,000, and Clovis were not the first ones we know of to overshot flake.
Solutreans were the first Europeans we know of to overshot flake.
And now, an archaeological discovery in 2010 in Blombos Cave, South Africa, "places the use of pressure flaking by early humans to make stone tools back to 73,000 BCE, 55,000 years earlier than previously accepted." Now, pressure flaking is a root to overshot flaking, but it arose independently in Africa before it did in Europe and the Americas.
So, that's three disparate cultures using similar techniques. Two are absolutely independent developments. There's no reason the third isn't. To claim that Americans couldn't have figured out a better way to shape stone is as ridiculous as the claims that they couldn't figure out how to stack small rocks on big ones to make pyramids, so the Egyptians must have settled Central America. Yes, some "researchers" claim that.
The Solutrean technique also seems to have gone out of fashion in Europe, and was replaced by careful pressure flaking, then by polishing, before bronze appears. In the Americas, various flaking technologies continued to evolve to a fine art due to isolation. There are similarities of technique weaving in and out, but all evidence is that the technologies were shared with nearby groups and dispersed, also depending on the type of material being worked.
Then, these are Solutrean points:

Source: Wikimedia.org
These are Clovis points:

Source: Wikimedia.org
Which are different, fluted, and in fact, more sophisticated than Solutrean points.
This brings is to "Could have, but didn't need to have" as far as the vague similarity of tools. The Solutrean Hypothesis isn't needed to explain this "similarity" because not only is it not, but there are only so many ways to shape flint. Much like there were probably three independent developments of iron, and at least three of agriculture, and several of bronze.
Except "the oldest Clovis site in North America is believed to be El Fin del Mundo in northwestern Sonora, Mexico, discovered during a 2007 survey. It features occupation dating around 13,390 calibrated years BP. In 2011, remains of gomphotheres were found; the evidence suggests that humans did, in fact, kill two of them there. Also, the Aubrey site in Denton County, Texas, produced an almost identical radiocarbon date."
Shortly thereafter, we find the Clovis tool industry in Washington State.
In fact, the African points look closer to Solutrean. But I don't think anyone would suggest there were direct lineal ties between them, even though they can be reached overland.

Source: Wikimedia.org
So as far as similarity of flint tools: There isn't. Done. All three cultures developed these basic techniques independently.
The Solutreans had a lot of cave art, carvings, even some bone instruments. The Eastern cultures of the Clovis industry, so far as we know, did not have comparable art or artifacts. When this issue was raised, in fact, the proponents replied: "Bradley and Stanford contend that it was 'a very specific subset of the Solutrean who formed the parent group that adapted to a maritime environment and eventually made it across the north Atlantic ice-front to colonize the east coast of the Americas' and that this group may not have shared all Solutrean cultural traits."
So which traits did they keep? Because we've debunked the claim of having the same tool set. They didn't use similar art, similar shelters, or instruments. At least not that we've found. You can't claim to share traits not in evidence, and so far, there's no evidence of ANY shared traits. Well, they both hunted meat, I guess.
Let's step back to the primary issue here. Are there genetic links? Because if a bunch of European Cro-Magnon came here, we should see their haplogroups.
Here’s a Clovis infant related to all American natives, and to many Asian natives, including the Yeniseians, currently believed to be descended from the ancestors of the Americans. What he is not related to are Europeans. He's Clovis era, and he is out west. Where the Clovis tool set seems to have originated.
The only European haplogroups we find in the east are post 1400, when various explorers and sailors were making land, and making native women.
Now, this doesn't disprove that Europeans came here and their lines died out entirely. But we'd need to find said haplogroup in a burial site, and we haven't. Nor is it likely. Europeans still carry some small percentage of Neanderthal DNA 40,000 years later, the result of (estimated) six surviving cross-breedings. (Many more may have happened. Only six lines have survived to the present.) So had these Solutreans come here, we would absolutely expect to find some genetic residue. We do not.
Linguistics are almost impossible to analyze at this distance. However, there is this which discusses the same general timeframe. The consensus is it's probably impossible to prove, but feasible. This hypothetically ties languages between those two continents. There's nothing so far to suggest any proto-European influence in native languages. Note that I include this just to cover all bases.
So at this point: Zero linguistic, genetic, aesthetic, or technical connection in evidence between Europe and the Americas at that time, and the Clovis industry started on the far side of the continent from Europe (per our current findings). And it started 3500 years later. Which means it's not the same culture. (This also irks me when modern natives insist that some find as old as Anzick has to be buried with "tribal traditions." That would be like me insisting a Neolithic find in the UK be given a "Christian burial." A Baptist one at that. There's no cultural relationship present.)
Nothing.
Now let's look at the hypothetical method by which these Solutreans arrived here.
Well, there isn't one. Perhaps they moved onto the ice sheets across the North Atlantic and eventually came off them in the Americas and traveled halfway down the coast and moved inland to share a dissimilar technology that first appears on the far side of the continent.
But while we're at it:
The Solutreans were the end of the Gravettian era (though used a different toolset and industry) in Europe. They lived in a relatively temperate Southern France and Iberia. This is a nice place to be during an ice age. It's a nice place to be now.
Why would they move north, onto the ice?
"Population pressure"?
Land ice is easier and safer to live on than sea ice. We have zero evidence of anyone doing so. I point that out because obviously no evidence would remain from sea ice. It would be at the bottom of the Atlantic. If it existed. Which seems very unlikely because no cultures we know of ever lived on the ice. They might hunt, fish and travel there, but they lived on solid land. These alleged displaced people would be better off moving inland, or south. Even into the North African desert would be better than the ice.
The problems with living on sea ice should be obvious:
o	Risk of falling through cracks and losing a tent or a village. You better hope it stays really cold.
o	Really cold is harder to survive and requires heat sources.
o	Pack ice has very limited building and boatbuilding materials—bone and skin only.
o	Pack ice has very limited food—fish, some marine mammals.
o	Pack ice has very limited fuel for the previously mentioned heat sources—whale or seal oil, and not a lot of it.
o	There’s almost no possible way to make a wick to burn the oil for heat or cooking. You could use a skull as a lamp base, but a wick? You need an easily flammable, porous substance. Moss, tow, fungus were all used. What do you use on pack ice? There's nothing. No fire.
o	Once you're on the ice, all your tools are going to be made of bone. The Dorset, Thule, Inuit and Athabaskans all did or do this.
But guess what?
They didn’t know how to flake flint.
So, the hypothesis is that some Solutreans move onto the ice, doing something that makes no sense, is virtually guaranteed to kill them all in a matter of weeks, magically survive, and spend 3000-4000 years surviving in a worse environment than any we've ever seen humans live in, working their way across the ice. . . .
Also, they'd have passed over the Faeroe Islands, Iceland, Greenland, Baffin Island, Labrador and Newfoundland, and somehow didn't leave any evidence of their passage, or this awesome flint-shaping technique there.
And, as noted, for the 3000-4000 years they're on the ice . . . no flint to shape. No written records to document the technique. But somehow, leaving Europe in 17,000 or earlier, they arrive in the Americas around 13,200 and remember how to pressure flake flint . . . in Sonora, Mexico. In a totally different shape.
Vs: A founder population from Asia, east of the Yenisei River and north of Lake Baikal, moved onto existing land either coastal or inland or both, and spread into the continent, leaving genetic, material, and potential linguistic evidence, using well-established technology we can observe in both places. For example: "Stemmed points are a lithic technology distinct from Beringian and Clovis types. They have a distribution ranging from coastal east Asia to the Pacific coast of South America. The emergence of stemmed points has been traced to Korea during the upper Paleolithic. The origin and distribution of stemmed points have been interpreted as a cultural marker related to a source population from coastal east Asia."
I think we're done here.
I guess the only question I have is why this pile of crap is considered an "Hypothesis."
Look, when researching my last fiction work, I came up with what some professional paleanthropolgists say is a valid hypothesis for the development of leather tanning. I'll quote:
"The chamber pot in the lodge is a hole lined with a hide. They close up the hide in the morning and dump it out, then rinse it. Hide plus fat plus piss equals tanning. Anything they didn't scrape fully would wind up tanned, and be very supple wet, very hard when dry. Once you know that, you have leather. Then when you use it as a windbreak or cover, the smoke colors and softens it."
Provable? Not easily. Few organic remains survive for tens of thousands of years. Does it explain all the facts in evidence? Yes. I guess I'm about as close as Trombetti was with the Yeniseian-Na Dene languages. What I came up with works, is probably unprovable. But, it's simple and it works. I'm good with that.
Now, I'm not an academic, and don't have an institution to help promulgate the idea, but I don't really care. If they ever prove it, cool. If not, it fits what we know of leather.

But I'd certainly be embarrassed if my fiction involved fantasy Europeans traveling across ice to America to share nothing. So why did anyone in the field give this the first bit of consideration? It's not even an hypothesis. As the basis for a 1940s fantasy setting, it's about right. But there's literally nothing about it that can't be explained more easily as immigration in the west, and it has literally supporting zero facts other than "this stone point looks sort of like this other stone point if you squint really hard and haven't actually done any flint shaping."
And as far as the 1940s, I’ve found discussion debunking a previous presentation of a variation of this hypothesis, that the north Asiatics were the progenitors of the Solutrean industry, dating to 1939. It wasn’t a new idea, and it wasn’t credible then.
I guess we need to keep the complete fails around to avoid repeating them.
AFTERWORD: One of the groups who love this hypothesis are a subsect of white nationalists who'd love for some irrelevant reason to prove early settlers were European. They did the same when Kennewick Man had some genetic links to the Caucasus region, meaning he had ancestors who were geographically Caucasian, which not the same as being European or White, especially not 9000 years ago. Which is 8000-15,000 years after previous founder populations anyway. I am not at all implicating my friends with these groups, but those groups absolutely adore and insist on these unfactual claims. But quite a few commenters have asked the leading question of, “Who taught the (early Native Americans) to do it?”
The base assumption here, as noted before, is that the paleoIndians couldn’t develop technologies of their own, when they provably did, and the assumption speaks volumes.

Michael Z. Williamson is retired military, having served twenty-five years in the U.S. Army and the U.S. Air Force. He has consulted on military matters, weapons and disaster preparedness for Discovery Channel and Outdoor Channel productions and is Editor-at-Large for Survivalblog, with 300K weekly readers. His novels A Long Time Until Now and That Was Now, This is Then make use of his extensive research into the Paleolithic era.