Stone Axe In the Paleolithic Age 2.5 million years ago, Homo habilis (handy man) in East

2.1.1 Stone Axe In the Paleolithic Age 2.5 million years ago, Homo habilis (handy man) in East

Africa began experimenting with stone tools. They had small brains, prominent jut- ting jaws, and walked on two feet—thereby freeing their hands for manipulating and carrying objects. Bands of 10–20 made their living as hunter–gatherers and as scavengers. They foraged for soft plants and nuts as other tree apes, and they learned to broaden their diets to include meat from animals. The carcasses of larger animals represented bounties, but they were difficult to handle. How would they rip open the tough hide and tear off a limb from the carcass, suitable to carry up the nearest tree before a lion or a leopard would show up to interrupt their meal, and to bring home to feed the family? Bone marrow is a rich source of fatty food, but accessing it requires crushing the bone to extract the contents. How would they flay the hides to make clothing? They had seen how lions and leopards used sharp teeth and claws, but nature had given them neither. Some of them had the inspiration and creativity to find a fieldstone with a broken edge that could be used as a cutting tool. It is likely that there were even older tools made from wood or horn, but they did not

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FIGURE 2.2 Paleolithic Oldowan chopper.

survive—thus, we have only a huge collection of stone hand axes, and have come to regard them as mankind’s first invention.

The stone axe is not a single invention that occurred only once in history, but a sequence of inventions that gradually improved over millions of years by different species of the human animal, forming a relay team of inventors and inventions. The first stone tools of the H. habilis, known as Oldowan choppers (Fig. 2.2) after the Olduvai Gorge in northern Tanzania where a large number of them were found, are crude products that could be easily mistaken for naturally broken pebbles. They can

be made by using a hammer stone to strike a fist-sized pebble at a sharp angle, to chip off a thin flake from the core. The core with the sharp edge can be used as a cutting or scraping tool for dismembering carcasses; digging for tubers, roots, and insects; and stripping bark from trees to access gum and insects. The blunt end can

be used for hammering open bones, and for pounding and cutting nuts and fruits. With this invention, humans could eat the food of lions, hyenas, and hogs. The best stone for this tool is a fist-sized pebble that is fine grained and uniform, so that it can be chipped and shaped into any desired form. Rocks with large grains such as granite, and rocks with layers such as slate, are not easy to shape into cutting edges; rocks with minute grains such as flint, and rocks that are glassy like obsidian, are the best. The rock should also be hard and heavy, so that the sharp edge created would remain sharp for a long time. H. habilis might have found pebbles on river banks with gravel bars of cobbles. It is more difficult to hammer out a piece from solid bedrock. At this stage of development, there were no standardized sizes, shapes and forms, and a tool of any shape with some sharp edges would serve a purpose.

Beginning 1.5–1.7 million years ago, a strikingly different and refined version of the stone axe first appeared among the Homo erectus, a new tribe with larger

2.1 TOOLS AND METHODS

FIGURE 2.3 Acheulian hand-axe. Reprinted courtesy of Library of Congress.

brains and smaller jaws. This tool, called the Acheulian hand-axe (see Fig. 2.3) was no longer a crude tool with a random shape, but was built according to a standard design that remained constant for more than 1 million years, and spread from Spain in the west to India in the east. The Acheulian hand-axe has an approximate length of 6 in. (150 mm) and a weight of 1.3 pounds (600 g), with a graceful tear-drop or pear shape. Its creators were more like sculptors who had a final form or template in mind. At one end, there is a point for piercing, two symmetrical cutting edges on the sides, and a blunt end for grasping and perhaps also for bashing bones and nuts. A hard stone hammer may have been used for the primary flaking to get the axe roughly into the desired approximate shape, then soft hammers of antlers and bones for the secondary flaking for better control of the finer work of trimming and detaching numerous small flakes. The best stones were European flint that was mined from chalk and chert limestone, as well as volcanic obsidian glass, but these valuable stones were available only in special locations and had to be obtained by long distance transportation and trade.

Homo sapiens , who made their first appearance around 200,000 years ago in Ethiopia, found many sophisticated uses for the stone flakes as tools, in addition to

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FIGURE 2.4 Neolithic stone tools. Reprinted courtesy of Library of Congress.

the cores. Modern humans appeared around 35,000 years ago, and created a great number of new stone tools. In the Neolithic Age (from 10,000 BCE), even more sophisticated stone implements (Fig. 2.4) were made with much finer control of the shape, sharper edges, and pleasing shapes. The flakes were used to flay hide and to pierce holes for making garments. The new tools were made with the technique of pressure flaking, which ingeniously substituted the hard-to-control hammer blows with steady pressure using bone, ivory, or hard wood against a stone edge, giving better control and producing smaller flakes. These microflakes could then be fastened to wooden shafts to make spears, arrows, and scythes for farming.

STRENGTH OF MATERIAL Paleolithic inventors were primarily concerned with whether their tools worked, but

scientists ask how they worked. Such knowledge leads to scientific understanding, and sources of future inventions. A scientific and quantitative description of the mechanical behavior of a material considers its response or strain under stress. A rod with an original

2.1 TOOLS AND METHODS

Brittle fracture

Elastic Ultimate Stress

FIGURE 2.5 Stress–strain graph of brittle and ductile materials.

length and cross-section area will become longer when stretched. The force per area is called the “stress,” and the resulting “strain” is the fractional change in the length of the rod. Figure 2.5 shows a stress–strain graph where the strain is plotted in the horizontal x axis against the stress in the vertical y axis. A brittle matter such as stone is shown in the solid curve. When the stress is small inside an elastic region, the deformation or strain is elastic and reversible, so that when the stress is released, the deformation will return to zero. When the material is stretched beyond the elastic region, the material suddenly breaks into two or more pieces at the point of ultimate strength. The amount of energy needed to break the material, the toughness, is measured by the triangular area underneath the solid curve.

The behavior for an elastic material, such as copper, is shown in the dotted curve. The elastic region is exceeded at the point of yield strength when the material begins to undergo irreversible or permanent plastic deformation; it eventually breaks at the point of ultimate strength. In comparison with brittle stone, copper needs less stress to deform, but more energy to break it.

Stone axes are made of hard materials, which are used to shape and manipu- late softer materials, such as hide and bones. The word “hard” has two separate meanings, referring to either a material’s resistance to bending and scratching, or its resistance to breaking. Diamond, for instance, is the hardest substance known that cannot be scratched, but it is brittle and can be shattered with a moderate force; on the opposite end is steel which is more flexible and easier to scratch, but is tougher and can sustain much heavier blows. Stone tools are extremely hard, and therefore make effective tools for cutting through softer materials. Their brittleness,

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however, means that they are easily shattered if struck against an object of superior toughness. While stone tools certainly represented an advance over fingers and teeth, they could not be used where flexibility and toughness were required, such as for making a sword or a lever. Even so, stone was the principal material for tools and weapons till the advent of the Bronze Age, only 50 years ago (or 3500 BCE). Flint knapping is the name given to making stone axes and other implements in modern times, which is done by experimental archeologists to understand the past. It is often taught to outdoorsmen for wilderness survival, and used to make flintlock firearms as a hobby.

The subsequent development and specialization of hand tools continued with metallic tools. In the middle ages, each village needed three craftsmen: a black- smith to work on metal objects and horseshoes, a carpenter to make furniture and wheels, and a mason to construct walls and houses. Each of them needed a set of tools to carry on their trades. In the modern world, we have many specialized indus- trial machines and tools, manmade sources of energy and power, and stronger materials to increase labor productivity and the quality of life.