The Strange and Fascinating Story of the World's Most Common Man-Made Material
By ROBERT COURLAND
Copyright © 2011 Robert Courland
All right reserved.
Chapter One Origins
Israeli geologists caused a minor stir in the 1960s when they announced the discovery of a concrete compound in a twelve-million-year-old rock formation in the Negev desert. This news raised eyebrows, particularly among engineering historians, archaeologists, and paleontologists, for the discovery predated not only the earliest known use of concrete but also the earliest known hominids. Twelve million years ago, our ancestors were hardly more advanced than today's lemurs. Who made the concrete?
Predictably, the facts are less sensational than the headlines. The pseudo-concrete was created when geologic forces gradually brought a limestone outcrop into contact with oil shale and, with water as a catalyst, produced a natural cement compound. This compound would not be considered concrete by chemists or engineers; rather, it could more accurately be described as "bad asphalt." For this reason, I think it best to confine our examination of concrete's origins to those early human societies whose approach to its invention, while sometimes not quite scientific, was more methodical and successful than Nature's random products.
Because lime—sometimes called "quicklime"—is the essential ingredient of concrete, it is perhaps best to begin our story with the discovery of that remarkable substance. Lime is derived from the principal component of limestone: calcium carbonate. Limestone is created from the physical remains of countless generations of corals and shellfish that eventually formed a thick sedimentary layer. This layer was eventually crushed and crystallized by powerful geologic forces, resulting in a whitish rock. Pick up a sun-bleached seashell lying on the beach, and you are, in effect, holding a pure form of limestone, for the shell consists almost entirely of calcium carbonate. Limestone in its abundance provides silent testimony to the massive volume of life that thrived in the oceans for hundreds of millions of years before human beings came into existence. And those human beings would eventually discover that limestone contained hidden properties that, to their primitive eyes, seemed nothing short of miraculous. Even for us today, long inured to technical wonders, these properties still seem a little eerie and preternatural.
We now know that lime was discovered sometime toward the end of the Paleolithic Age, approximately twelve thousand years ago. The Paleolithic (Old Stone) Age reaches back almost three million years, and technically begins with the first stone tools. Consequently, it encompasses both the hominids and anatomically modern humans who used stone tools. For Homo sapiens, the Paleolithic Age begins with our species, approximately two hundred thousand years ago.
Until the invention of carbon-14 analysis and other sophisticated dating technologies, it was often difficult for archaeologists to differentiate the age of objects found at various sites where our Paleolithic ancestors once lived. Were the objects one hundred thousand years old? Sixty thousand years old? There was sometimes not enough variation among the artifacts to easily chart a firm evolutionary path in toolmaking. For us, technological breakthroughs happen constantly within a single lifetime; for our hunter-gatherer ancestors, they took place perhaps once every hundred generations or more. For most of our existence on this planet, we were pretty slow on the uptake when it came to technology.
Then something happened between fifty and sixty thousand years ago. Stone tools gradually improved, and the diversity of artifacts increased. Around this time, the earliest bow was invented, and the sophistication of spear and axes improved. The first artwork arose; people began painting on cave walls and carving primitive figures in bone. One result of these small but immeasurably important developments was that when our ancestors first entered Europe forty thousand years ago, they possessed a decisive technological edge over the Neanderthals they encountered there. If modern humans had immigrated to Europe twenty thousand years earlier, this might be a completely different book.
After this technological uptick, a period of stasis returned that lasted millennia. The Neolithic (New Stone) Age began around 10,000 BCE. Compared to the slow pace of change during the Paleolithic Age, the Neolithic Age witnessed an explosive transformation in human societies and technologies. Ceramic figurines appeared, followed by pottery. Sheep were domesticated, and cloth weaving appeared soon after. Intertribal communities arose with shared languages and belief systems, and the larger labor pool led to the first great building projects. During this time, agriculture was gaining importance, increasingly supplementing the diet of hunter-gatherers with sowed grains and legumes. The modest leisure time afforded by food surpluses allowed for the discovery and development of new crafts. Some villages grew to become towns, and some of these towns would become the first cities.
Complex human societies had begun to emerge, and with them, what we may broadly call "civilization" had also arrived.
Archaeologists believed for a long time that the dramatic changes that took place during the Neolithic Age were primarily due to the discovery of agriculture and animal domestication. Only recently have we come to realize that the story is much more complicated than that. Technological and societal revolutions began centuries before agriculture arose. The old demarcations between the Neolithic and Paleolithic Ages have recently been pushed back and become blurred. These societal changes may have begun with the discovery of that remarkable substance: lime.
The most popular theory of lime's discovery is the "campfire on limestone" scenario. It runs something like this: At some point in the distant past, a group of hunter-gatherers pick a convenient spot for foraging and settle in for a few weeks or months. As a safety precaution, they locate their fire pit in a small depression on a stony outcrop well isolated from any dry brush. On this occasion, they build their fire in a limestone declivity. After some days or weeks have passed, they notice that the stone near the flames becomes desiccated and breaks off into clumps that easily collapse into a white powder. This is lime. After the fire has been extinguished and the pit becomes cool, someone picks up one of the clumps and crushes it in his hand. He feels a slightly painful irritation caused by the caustic powder. After first shaking his hand violently to remove the powder, he then pours some water on the affected skin to remove the nuisance. This normal response to an irritant is, on this occasion, not a very wise move. The water provokes a powerful reaction with the powder, and what had merely caused irritation a moment earlier now produces a chemical burn. Frenzied with pain, he continues to pour water on his palm and fingers. Fortunately, the more water he pours, the greater the dilution of the reactive compound, and soon the pain is lessened. Red, blistery patches—the scarring caused by second-degree burns—remain on his hand.
Of course, the victim goes to a doctor. It does not matter that the physician in question is a witch doctor, for the tribe's medical practitioner is not only the font of countless spells accumulated from an oral tradition that dates back from time immemorial, but he is also the chief pharmacist, possessing a repertoire of cures or palliatives that comprise hundreds of plant and animal parts. Perhaps less than a quarter of the ingredients in his medical arsenal represent true cures or analgesics, and the rest are placebos. However, between the panaceas and a few real herbal remedies, the shaman probably enjoys a high success rate—most people survive their illnesses naturally—which reinforces his people's faith in him.
After he dresses his patient's wound and gives him the Paleolithic equivalent of two aspirins, the shaman decides to investigate the curious powder that caused the problem. He knows that people confronted with a painful experience are not the best witnesses, and so he probably doubts the story about water causing the powder to burn. After all, water is used to put out fires, right? Bathing in it on a hot day cools the body and drinking it slakes one's thirst. It soothes pain but does not cause it.
The shaman goes to the fire pit and uses a stick to scrape some of the powdery rock into a small basket or clay bowl. Perhaps he first sticks the tip of his left pinkie into the powder and discovers that, yep, it is a mild irritant. Then he adds a little water to the powder. What happens next no doubt amazes him: the mixture begins to generate a flameless heat. His patient was not deranged after all; this is some serious stuff. As he continues to watch the bubbling concoction, he observes that after a few minutes the foaming dies down and the heat diminishes. If the witch doctor is patient, he will notice that the substance soon becomes solid. He taps the material with a stick and confirms that it has become very hard. A rock has been created!
Today we know what the shaman did not: that the heat of the fire transformed the calcium carbonate of the limestone. All the carbon dioxide and water within the rock (yes, all rocks contain a small degree of water) will have evaporated, leaving behind calcium oxide: the caustic powder we call lime or quicklime. When water is added to the powder, a violent chemical reaction takes place: heat is generated—up to 150°C (over 300°F)—and calcium hydroxide is formed. This new compound craves the carbon dioxide it lost during the baking process and so pulls it from the atmosphere like some alien creature dying of asphyxiation. Calcium carbonate begins to form within the mixture, and after a short time, it hardens and becomes, in effect, limestone once again. This artificially created calcium carbonate is very white and very hard. One might view it as the purest form of concrete.
Until very recently, the importance of this discovery was not fully appreciated. Archaeologists reasoned that a humble substance created by a simple campfire could not have had that much effect on the course of human technological development. This perspective was almost universally held until the 1990s, when new excavations and a closer look at the empirical evidence would challenge that assumption. Indeed, it is possible that the revolutions that led to the Neolithic Age may have begun with the invention of concrete, and that lime's discovery was far stranger and more interesting than anyone had previously supposed.
A RADICAL NEW VIEW OF THE LATE STONE AGE
In 1963, members of a joint American-Turkish archaeological survey team from the University of Istanbul and the Oriental Institute of the University of Chicago combed the landscape of southeastern Turkey, looking for sites to catalog for possible future excavation. In the small province of anliurfa, not far from the Syrian border, they found an exceptional number of potential sites for exploration. Toward the end of their survey in the province, the archaeologists came to a large hill with a rounded top that the Turks called Göbekli Tepe, which means "potbellied mount." The hill is a little over 300 m (ca. 1,000 ft) high and lies at the base of the Taurus Mountains. Nothing about the hill sets it apart from the others, except that its particular position provides superb views in all directions, the most spectacular being the mountains to the north and the Harran Plain to the south. However, the hill's immediate vicinity holds a particular and powerful interest for historians and biblical scholars. Turkey has a very rich past, and the southeastern region of the country, known since ancient times as Anatolia, has an even richer heritage. The tiny Anatolian province of anliurfa is especially drenched in prehistory, history, myth, and—incorporating varying mixtures of all three—tales central to Judeo-Christian and Islamic traditions.
Over the millennia, this diminutive region has been conquered and ruled by the Sumerians, Akkadians, Babylonians, Assyrians, Hittites, Hurris, Aramaeans, Medes, Persians, Macedonians, Romans, Parthians, Armenians, Arabs, Kurds, Crusaders, and, finally, the Turks. Near Göbekli Tepe is the ancient city of Harran, for which the plain is named. According to local Islamic tradition, Harran was the first spot where Adam and Eve stopped after their expulsion from the Garden of Eden. The Bible tells us that Harran is also the place where Terah and his son, Abram (the future patriarch Abraham), Abram's wife, Sarah, and their son, Lot (whose future wife would morph into sodium chloride) settled in for a spell on their oft-delayed journey from Ur to Canaan.
Also nearby is the province's eponymous capital, anliurfa, more commonly known as Urfa. According to Turkish Islamic tradition, Urfa was originally the city of Ur, the birthplace of the aforementioned Abraham. (Most archaeologists place Ur in today's Iraq.) According to Jewish legend, it was in Ur that Abraham was thrown into a great bonfire by the nasty Babylonian king Nimrod. God intervened on Abraham's behalf, and he walked out of the flames unscathed. Turkish Islamic tradition explains why: God had turned the flames into water and the firebrands into fishes. To commemorate Abraham's deliverance from the flames, Urfa has for many centuries maintained a sacred pool of fishes next to the mosque dedicated to the patriarch.
Moving on to more verifiable history, the plain just outside Harran was the scene of some of the most significant battles in antiquity. It was on the Harran Plain where the Babylonians defeated the Assyrians in 610 BCE; where Xenophon and his Ten Thousand marched by in 401 BCE, harried by the Kurds along the way; where Marcus Licinius Crassus, the Roman general who had defeated the rebel slaves led by Spartacus, was himself defeated by the Parthians in 53 BCE; where the Roman emperor Caracalla was assassinated by one of his lieutenants during another campaign against the Parthians in 217; where another Roman emperor, Valerian, was decisively beaten by the Persians in 260 and taken captive; and where the crusaders fought the Turks in the Battle of Harran in 1104 (the Crusaders lost).
In short, today's tiny anliurfa province has seen the rise and fall of many kings, sultans, shahs, emperors, emirs, and pashas, as well as their respective kingdoms, empires, and emirates. Hardly a day goes by without some farmer discovering an ancient artifact while digging a well or tilling a field.
By the time the archaeologists came to Göbekli Tepe, they had already recorded a number of exciting sites for excavation and were getting a little jaded by this surfeit of riches. Some requisite exploratory digging at Göbekli Tepe uncovered a large number of ancient flint and obsidian tools. However, a few carefully carved limestone blocks poking out of the ground seemed to belong to a much later period. The director of the survey, Peter Benedict, guessed that a Byzantine church and cemetery overlay a more ancient settlement. In a region abundant in important sites, Göbekli Tepe did not appear all that interesting. Benedict noted the geographical coordinates of the hill, wrote a brief description of the stone tools and carved stone blocks found there, and gave the site a name that, while hardly prosaic, was eminently practical for cataloging purposes: "V 52/1." Bennett and the other members of the survey team then moved on to look for other potential sites. None of them would have guessed that the hill would one day be the site of one of most important archaeological discoveries of all time and provide the final piece of an archaeological puzzle that had taken over a half century to put together. For, in addition to its religious and historical claims to fame, Lilliputian Sanliurfa province would be revealed as the birthplace of civilization.
Excerpted from CONCRETE PLANET by ROBERT COURLAND Copyright © 2011 by Robert Courland. Excerpted by permission of Prometheus Books. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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